Calculate first, then download your square footage as a plain text file.

A square footage calculator multiplies the length of an area by its width, both measured in feet, to give the area in square feet.

To calculate square footage of a room, measure the length and the width in feet, turn any leftover inches into a decimal by dividing them by 12, then multiply the two numbers. A room 12 ft 6 in long and 10 ft 3 in wide is 12.5 × 10.25 = 128.13 square feet. For a shape that is not a rectangle, split it into rectangles, triangles and part circles, work out each piece, and add them up.

Rule of thumb: always add a waste allowance before you buy. Use 10% for a straight lay, 15% for diagonal or herringbone, and 20% for a patterned or heavily cut floor.

Square footage is the size of a flat surface measured in square feet. One square foot is the area of a square that is one foot long on every side. If you could tile a room with squares that each measure 12 inches by 12 inches, the number of tiles you would need is the square footage of that room.

It is a measure of area, not of length. Length answers "how far", area answers "how much surface". That is why square footage is written as ft² or sq ft, with the small two meaning the unit has been multiplied by itself.

3.1 A worked one-liner

A bedroom that is 12 feet 6 inches long and 10 feet 3 inches wide has 12.5 × 10.25 = 128.13 square feet of floor.

3.2 What a square foot actually looks like

3.3 Who uses square footage and why

• Home owners buying flooring, carpet, tile, laminate, turf or paint.
• Renters and buyers comparing two homes by size rather than by photos.
• Landscapers ordering mulch, topsoil, gravel or grass seed for a lawn or a yard.
• Builders and estimators pricing work per square foot.
• Landlords and agents quoting rent per square foot for offices and shops.
• Insurers and valuers estimating rebuild cost from floor area.

3.4 Square footage against the nearest alternatives

A common and expensive mistake is ordering skirting board by square footage. Skirting is bought by linear feet, which is the distance around the room, not the area of the floor.

Your square footage tells you how much flat surface you have to cover, price, or fill. Under 100 sq ft is a small area, 100 to 200 sq ft is an average sized room, 200 to 400 sq ft is a large room, and anything over 1,000 sq ft is whole home scale. Compare your number against those bands, then add a waste allowance before you buy.

4.1 What your square footage means

4.2 Where your area sits against typical rooms

4.3 How much material you actually need to buy

4.4 The same area in other units

4.5 Why the number changes when you round

Rounding a measurement to the nearest foot changes the answer more than people expect, because the error is multiplied twice. Rounding 12 ft 6 in down to 12 ft and 10 ft 3 in down to 10 ft turns 128.13 sq ft into 120 sq ft. That is 6.3% less, which is most of a waste allowance thrown away. Always keep the inches.

4.6 What changes your square footage

• Alcoves, bays and chimney breasts. Measure them as separate small rectangles and add or subtract them, or use the L-shape, U-shape or cut out options.
• Fitted furniture. For flooring, most installers still run the floor under fitted units, so measure the full room.
• Doorways and thresholds. A door reveal adds a small rectangle of floor that still needs covering.
• Out of square walls. If two opposite walls differ by more than an inch, measure both and use the longer one.
• Sloping ceilings. Floor area does not change, but usable area and some legal definitions do.

4.7 What to do next

1. Write down your square footage and the waste percentage you used.
2. Check the coverage printed on the box of the product you want.
3. Divide the total needed by the coverage and round up to a whole box.
4. Buy one extra box for future repairs if the product is likely to be discontinued.
5. Keep the offcuts until the job is signed off.

4.8 Common mistakes this calculator prevents

• Treating 12 ft 6 in as 12.6 ft. It is 12.5 ft, because inches are twelfths, not tenths.
• Multiplying feet by inches and getting a number with no meaning.
• Dividing square feet by 3 to get square yards. The correct divisor is 9.
• Forgetting the waste allowance and running out of flooring on the last row.
• Using a room's square footage to buy skirting board, which is sold by the linear foot.
• Adding up rooms measured in different units without converting first.

4.9 A sanity check you can do in your head

Use your square footage three ways: to order material, to price a job, and to compare spaces. Multiply the area including waste by the price per square foot to get a budget, divide it by the coverage on the box to get a box count, and quote the same figure in square metres when talking to a metric supplier. Never order trim or skirting from it.

Five ready to copy blocks. Each one fills in with your own numbers once you press Calculate.

The square footage formula for a normal room is the first card. The cards below it move outward to inches, other shapes, unit conversions, material and volume. Every one of the twenty shapes in the dropdown is listed with its own formula in Table 11.8.

Ten steps, carried through one worked example: a bedroom 12 ft 6 in by 10 ft 3 in that is getting laminate flooring at $3.50 per square foot.

1. Choose your measurement unit. Nine are offered, from feet and inches through to millimetres and kilometres. Leave it on "Feet and inches" if you measured with a tape. Our bedroom was measured that way.
2. Choose the shape. The dropdown holds twenty shapes in five groups. A normal four walled room is "Rectangle or room", which is what our bedroom is.
3. Type the length. Enter 12 in the feet box and 6 in the inches box. The calculator turns that into 12.5 ft.
4. Type the width. Enter 10 in the feet box and 3 in the inches box, which becomes 10.25 ft.
5. Set how many identical areas. Leave it at 1 for a single bedroom. Set it to 3 if you have three bedrooms of the same size.
6. Open Advanced options. Set the waste allowance to 10% for a straight lay laminate.
7. Enter the coverage and the price. Our laminate covers 20 sq ft per box and costs 3.50 per square foot.
8. Add more rooms if you want a whole home total. Open "Add more rooms" and enter each extra room's length and width in plain feet.
9. Press Calculate Square Footage. The panel on the right shows 128.13 sq ft and its size band straight away.
10. Read Section 2 and download. You get 14.24 square yards, 11.90 square metres, 0.0029 acres, 140.94 sq ft to buy, 8 boxes and a cost of about $493.28. Use Download TXT or Download PDF to keep it.

This section shows how to calculate square footage in Excel or Google Sheets, using the same bedroom as everywhere else on this page: 12 ft 6 in by 10 ft 3 in, which is 128.13 sq ft.

8.1 The functions you need

CONVERT needs the Analysis ToolPak in very old versions of Excel. In Excel 2010 and later, and in Google Sheets, it is built in.

8.2 Step by step

8.3 The awkward cases

• Fractions of an inch. Type =12+6.5/12 for 12 ft 6½ in. Typing 6 1/2 into a plain cell may be read as a date.
• A whole measurement typed as text. 12' 6" is text, not a number, and multiplying it gives #VALUE!. Keep feet and inches in separate numeric columns.
• Circles. Use =PI()*(A2/2)^2 with the diameter in A2. Squaring the diameter instead of the radius gives an answer four times too large.
• Three sided plots. Heron's formula in one cell: =SQRT(((A2+B2+C2)/2)*(((A2+B2+C2)/2)-A2)*(((A2+B2+C2)/2)-B2)*(((A2+B2+C2)/2)-C2)).
• Acres. 0.0029 acres displays as 0.00 with the default two decimal places. Increase the decimals on that cell.

8.4 Why answers differ across software

• Display rounding versus stored value. This tool rounds only for display and calculates at full precision, which is what Excel does too. A calculator that rounds each room to two decimals before adding will drift by a few hundredths across a whole house.
• The square metre constant. This tool and Excel's CONVERT both use 0.09290304 exactly. Some websites use 0.0929, which is 0.003% low, about 0.004 m² on our bedroom.
• Rounding boxes. Excel's ROUND(7.047,0) gives 7. ROUNDUP gives 8. This tool always rounds boxes up, because 7 boxes does not finish the floor.
• Pi. PI() carries 15 digits. A page using 3.14 is 0.05% low on a circular area.

8.5 Charting it in Excel

Select the room names and the square footage column, then Insert, Charts, Pie for the share each room contributes, or Insert, Charts, Bar for a straight comparison. Add data labels and set them to show the value, so the square footage is printed on the chart itself. To show your room against typical sizes, add a second series holding the typical values and choose a clustered bar chart.

8.6 Error messages and what they mean

Google Sheets: every formula above works unchanged. The one difference is that Sheets has no Analysis ToolPak, because CONVERT is always available.

One script, complete and runnable from top to bottom. It uses the same three rooms as Section 8, so the bedroom comes out at 128.13 sq ft.

9.1 The complete script

# ============================================================
# Square Footage Calculator in R
# Stats Unlock - statsunlock.com
# Change only the MEASUREMENTS block below, then run the whole file.
# ============================================================

# ---- 1. MEASUREMENTS (change these) -------------------------
rooms <- data.frame(
  room       = c("Bedroom", "Hall", "Kitchen"),
  length_ft  = c(12, 8, 11),      # whole feet
  length_in  = c(6,  0, 3),       # leftover inches
  width_ft   = c(10, 4, 9),
  width_in   = c(3,  6, 9),
  stringsAsFactors = FALSE
)

waste_pct     <- 10      # 10 straight lay, 15 diagonal, 20 patterned
coverage_sqft <- 20      # square feet per box, from the carton
price_per_sqft<- 3.50    # your currency per square foot
depth_inches  <- 4       # depth for cubic yards, 0 to skip

# Reading from a file instead:
# rooms <- read.csv("rooms.csv", stringsAsFactors = FALSE)
# rooms <- rooms[complete.cases(rooms), ]   # drop rows with missing values

# ---- 2. CONVERT FEET AND INCHES TO DECIMAL FEET -------------
to_feet <- function(ft, inches) ft + inches / 12

rooms$L <- to_feet(rooms$length_ft, rooms$length_in)
rooms$W <- to_feet(rooms$width_ft,  rooms$width_in)

# ---- 3. SQUARE FOOTAGE --------------------------------------
rooms$sqft <- rooms$L * rooms$W

total_sqft <- sum(rooms$sqft)

# ---- 4. CONVERSIONS AND MATERIALS ---------------------------
sq_yards  <- total_sqft / 9
sq_metres <- total_sqft * 0.09290304
acres     <- total_sqft / 43560
sq_inches <- total_sqft * 144

to_buy <- total_sqft * (1 + waste_pct / 100)
boxes  <- if (coverage_sqft > 0) ceiling(to_buy / coverage_sqft) else NA
cost   <- to_buy * price_per_sqft
cu_yd  <- if (depth_inches > 0) total_sqft * depth_inches / 324 else NA

# ---- 5. PLAIN ENGLISH VERDICT -------------------------------
band <- as.character(cut(total_sqft,
  breaks = c(-Inf, 100, 200, 400, 1000, Inf),
  labels = c("a small area", "an average sized room", "a large room",
             "a very large space", "whole home scale"),
  right  = FALSE))

cat("\n=== SQUARE FOOTAGE RESULT ===\n")
print(round(rooms[, c("room", "L", "W", "sqft")], 2))
cat(sprintf("\nTotal square footage : %.2f sq ft\n", total_sqft))
cat(sprintf("That is %s.\n", band))
cat(sprintf("Square yards         : %.2f\n", sq_yards))
cat(sprintf("Square metres        : %.2f\n", sq_metres))
cat(sprintf("Acres                : %.4f\n", acres))
cat(sprintf("Square inches        : %.0f\n", sq_inches))
cat(sprintf("Buy with %g%% waste   : %.2f sq ft\n", waste_pct, to_buy))
if (!is.na(boxes)) cat(sprintf("Boxes needed         : %d\n", boxes))
cat(sprintf("Estimated cost       : %.2f\n", cost))
if (!is.na(cu_yd)) cat(sprintf("Cubic yards at %g in : %.2f\n", depth_inches, cu_yd))

# ---- 6. FIGURE AT 300 DPI -----------------------------------
png("square_footage.png", width = 2400, height = 1500, res = 300)
op <- par(mar = c(5, 7, 4, 2))
bp <- barplot(rooms$sqft,
              names.arg = rooms$room,
              horiz = TRUE, las = 1,
              col = "#1d4ed8", border = NA,
              xlab = "Square feet",
              main = sprintf("Square footage by room (total %.2f sq ft)", total_sqft),
              xlim = c(0, max(rooms$sqft) * 1.25))
text(rooms$sqft, bp, labels = sprintf("%.2f", rooms$sqft), pos = 4, cex = 0.8)
par(op)
dev.off()
cat("\nSaved square_footage.png at 300 dpi\n")
cat("Generated by STATS UNLOCK - statsunlock.com\n")

There is no install.packages() step. This script runs in any R installation.

9.2 What each part of the script does

9.3 What the figure shows

A horizontal bar chart, one bar per room, with the square footage printed at the end of each bar and the total in the title. The x axis is stretched 25% past the longest bar so the labels are never clipped. At 300 dpi and 2400 pixels wide the file is print quality, which is what a report or a quote needs.

9.4 Problems and fixes

9.5 One-liners

The same three rooms again, so the bedroom is 128.13 sq ft and the three room total is 273.81 sq ft.

10.1 The complete script

# ============================================================
# Square Footage Calculator in Python
# Stats Unlock - statsunlock.com
# Change only the MEASUREMENTS block below, then run the whole file.
# pip install pandas matplotlib
# ============================================================

import math
from decimal import Decimal, ROUND_HALF_UP

import pandas as pd
import matplotlib
matplotlib.use("Agg")
import matplotlib.pyplot as plt

# ---- 1. MEASUREMENTS (change these) -------------------------
rooms = pd.DataFrame({
    "room":      ["Bedroom", "Hall", "Kitchen"],
    "length_ft": [12, 8, 11],     # whole feet
    "length_in": [6,  0, 3],      # leftover inches
    "width_ft":  [10, 4, 9],
    "width_in":  [3,  6, 9],
})

waste_pct      = 10      # 10 straight lay, 15 diagonal, 20 patterned
coverage_sqft  = 20      # square feet per box, from the carton
price_per_sqft = 3.50    # your currency per square foot
depth_inches   = 4       # depth for cubic yards, 0 to skip

# Reading from a file instead:
# rooms = pd.read_csv("rooms.csv")
# rooms = rooms.dropna()          # drop rows with missing values

# ---- 2. CONVERT FEET AND INCHES TO DECIMAL FEET -------------
def to_feet(ft, inches):
    return ft + inches / 12

rooms["L"] = to_feet(rooms["length_ft"], rooms["length_in"])
rooms["W"] = to_feet(rooms["width_ft"],  rooms["width_in"])

# ---- 3. SQUARE FOOTAGE --------------------------------------
rooms["sqft"] = rooms["L"] * rooms["W"]
total_sqft = rooms["sqft"].sum()

# Python's built-in round() uses banker's rounding, so round(128.125, 2)
# gives 128.12 while Excel gives 128.13. Use this helper to match Excel.
def round_half_up(x, places=2):
    q = Decimal(10) ** -places
    return float(Decimal(str(x)).quantize(q, rounding=ROUND_HALF_UP))

# ---- 4. CONVERSIONS AND MATERIALS ---------------------------
sq_yards  = total_sqft / 9
sq_metres = total_sqft * 0.09290304
acres     = total_sqft / 43560
sq_inches = total_sqft * 144

to_buy = total_sqft * (1 + waste_pct / 100)
boxes  = math.ceil(to_buy / coverage_sqft) if coverage_sqft > 0 else None
cost   = to_buy * price_per_sqft
cu_yd  = total_sqft * depth_inches / 324 if depth_inches > 0 else None

# ---- 5. PLAIN ENGLISH VERDICT -------------------------------
if total_sqft < 100:
    band = "a small area"
elif total_sqft < 200:
    band = "an average sized room"
elif total_sqft < 400:
    band = "a large room"
elif total_sqft < 1000:
    band = "a very large space"
else:
    band = "whole home scale"

print("\n=== SQUARE FOOTAGE RESULT ===")
print(rooms[["room", "L", "W", "sqft"]].round(2).to_string(index=False))
print(f"\nTotal square footage : {round_half_up(total_sqft):.2f} sq ft")
print(f"That is {band}.")
print(f"Square yards         : {round_half_up(sq_yards):.2f}")
print(f"Square metres        : {round_half_up(sq_metres):.2f}")
print(f"Acres                : {round_half_up(acres, 4):.4f}")
print(f"Square inches        : {sq_inches:.0f}")
print(f"Buy with {waste_pct}% waste   : {round_half_up(to_buy):.2f} sq ft")
if boxes is not None:
    print(f"Boxes needed         : {boxes}")
print(f"Estimated cost       : {round_half_up(cost):.2f}")
if cu_yd is not None:
    print(f"Cubic yards at {depth_inches} in : {round_half_up(cu_yd):.2f}")

# ---- 6. FIGURE AT 300 DPI -----------------------------------
fig, ax = plt.subplots(figsize=(8, 5), dpi=300)
ax.barh(rooms["room"], rooms["sqft"], color="#1d4ed8")
for y, v in enumerate(rooms["sqft"]):
    ax.text(v * 1.01, y, f"{round_half_up(v):.2f}", va="center", fontsize=8)
ax.set_xlabel("Square feet")
ax.set_xlim(0, rooms["sqft"].max() * 1.25)
ax.set_title(f"Square footage by room (total {round_half_up(total_sqft):.2f} sq ft)")
ax.invert_yaxis()
fig.tight_layout()
fig.savefig("square_footage.png", dpi=300)
plt.close(fig)

print("\nSaved square_footage.png at 300 dpi")
print("Generated by STATS UNLOCK - statsunlock.com")

Install the two third-party packages with pip install pandas matplotlib.

10.2 What each part of the script does

10.3 What the figure shows

The same horizontal bar chart as the R script, one bar per room, values printed at the end of each bar, the total in the title, and the y axis inverted so the first room in your table appears at the top. It is saved at 300 dpi, which is print quality.

10.4 Problems and fixes

10.5 One-liners

Nine lookup tables. This is the square footage chart section: use it to check an answer, to convert a unit, or to sanity check a room size without typing anything.

Table 11.1 Inches to decimal feet

What to conclude: inches are twelfths, not tenths. 6 inches is 0.5 ft and 3 inches is 0.25 ft. If you ever write 12.6 ft for 12 ft 6 in, your area will be about 1% too large.

Table 11.2 Square footage chart for common room sizes

What to conclude: most bedrooms land between 100 and 200 sq ft. If your answer is far outside that, check whether you measured in inches by mistake, or missed a foot on the tape.

Table 11.3 Square feet to other area units

What to conclude: one acre is exactly 43,560 sq ft and exactly 4,840 sq yd. To convert square footage to acres, divide by 43,560. To convert acres to square footage, multiply by 43,560.

Table 11.4 Waste allowance by installation type

What to conclude: waste is not optional. The most common flooring complaint is running short on the final row, and a part box costs far more per square foot than the original order.

Table 11.5 Coverage per box and boxes needed

What to conclude: always round the box count up. Coverage figures are the manufacturer's, so check the carton, because they vary by range and by country.

Table 11.6 Square feet to cubic yards by depth

What to conclude: the whole table comes from one line, cubic yards = square feet times depth in inches divided by 324. Concrete suppliers usually sell in quarter yard steps, so round up to the next quarter.

Table 11.7 Which unit each trade sells in

What to conclude: square footage is the right measure for surfaces. It is the wrong measure for anything sold by length or by volume, and that is where most over ordering and under ordering happens.

Table 11.8 Every shape and its square footage formula

What to conclude: every one of these is in the shape dropdown at the top of the page, grouped into straight sided, triangles, curved, regular polygons, and combined or cut out. If your area is not on this list, split it into pieces that are, work out each one, and add them together.

Table 11.9 The nine measurement units and how each converts to feet

What to conclude: the calculator converts everything to decimal feet first, then multiplies. Switching the unit converts the numbers you have already typed at full precision, so you can measure in millimetres and still read the answer in square feet.

Eight worked examples that cover the whole range: a textbook room, a whole home, a tiny closet, a borderline case, an extreme size, a case where the obvious reading is wrong, an invalid input, and one real world job.

Measure a room for square footage with a metal tape, at floor level, wall to wall. Take the length along one wall and the width along the wall next to it, then measure both of each pair of opposite walls, because few rooms are truly square. Write feet and inches separately, add alcoves and bays as their own rectangles, and measure everything twice.

Almost every wrong answer comes from a wrong measurement, not from wrong arithmetic. These twelve steps take about ten minutes for a normal room.

1. Use a metal tape, not a cloth one. A cloth tape stretches, and a 25 ft metal tape locks so you can read it alone.
2. Clear the edges. Push furniture back from at least one long wall and one short wall so the tape lies flat.
3. Measure at floor level. Skirting boards, radiators and window sills all sit above the floor, and measuring at waist height gives a bigger room than the one you are covering.
4. Hook the tape into the corner. Push the hook hard against the wall, keep the tape straight, and read it where it meets the far wall.
5. Read to the nearest half inch, then round up. Rounding up gives you a small safety margin, which is the right direction to be wrong in.
6. Measure both opposite walls. Very few rooms are truly square. If the two lengths differ, use the longer one.
7. Measure alcoves and bays separately. Each one is a small rectangle. Write it down as its own room in the extra rooms list.
8. Include the door reveal. The strip of floor inside the door frame still needs covering, usually about 5 inches deep by the door width.
9. Subtract only permanent fixtures. Take off a kitchen island or a built in hearth. Do not take off a bed or a sofa.
10. Write feet and inches separately. Write "12 ft 6 in", never "12.6", and never mix the two on one page.
11. Sketch the room and label it. A rough plan with the numbers on it catches mistakes that a list of numbers hides.
12. Measure it all again. A second pass takes two minutes and catches the misread foot that would have cost you a box of flooring.

13.1 The inputs, their units and their typical ranges

13.2 Common measuring mistakes

• Writing 12.6 for 12 ft 6 in. The correct decimal is 12.5.
• Measuring over the skirting board rather than at the floor.
• Measuring only one of each pair of walls in an out of square room.
• Letting the tape sag across a long room, which shortens the reading.
• Forgetting the bay window, which is often 8 to 12 sq ft on its own.
• Adding rooms measured in metres to rooms measured in feet.
• Measuring the ceiling instead of the floor in a room with a sloping roof.

Use a square footage calculator whenever you are buying something sold by area: flooring, carpet, tile, turf, paint or concrete. It is also the right tool for comparing room sizes and for converting between square feet, square metres and acres. Do not use it for a legal floor area on a sale or mortgage, or for anything sold by the linear foot.

14.1 Four quick examples

1. Laminate for one bedroom. Rectangle, feet and inches, 10% waste, coverage 20 sq ft. This calculator is exactly right.
2. Turf for a back lawn. Rectangle or L-shape in plain feet, then subtract beds as extra rooms with a minus. Right tool.
3. Skirting for the same bedroom. Wrong tool. You need the perimeter, which is 2 × (12.5 + 10.25) = 45.5 linear feet.
4. Listing a house for sale. Wrong tool for the legal figure, but useful for a rough check before the surveyor arrives.

14.2 Which tool you actually need

16.1 Assumptions

1. The area is flat. If the surface slopes or curves, the true surface area is larger than this figure, so you will under order.
2. The corners are square. If the room is out of square, using the longer of each pair of walls slightly over estimates, which is the safe direction.
3. Your measurements are accurate to about half an inch. A one inch error on a 12 ft wall changes the area by roughly 0.7%, so you under or over order by that much.
4. The shape you picked matches the real one. Treating an L-shape as a rectangle over estimates, sometimes by 20%, as Example 6 shows.
5. The waste percentage suits your installation. Too low and you run short. Too high and you pay for boxes you return or store.
6. The coverage on the box is right. Manufacturers state nominal coverage. Real coverage can be a fraction lower, so a very tight box count can fail.
7. The price per square foot is the delivered price. If it excludes underlay, adhesive, delivery or fitting, the total will be low.
8. Depth is uniform. For concrete or mulch, an uneven base means more material than the cubic yards figure suggests.

16.2 Limitations, and what to use instead

If you used this square footage calculator in a report, a quote, a dissertation or a listing, cite it like this.

19.1 APA 7th edition

19.2 BibTeX

19.3 A plain reference for a document

19.4 How this calculator was built and checked

Trust in a calculator comes from being able to see how it works, so here is the method in full.

• Formula sources. Every area formula on this page is standard plane geometry, not a proprietary variant. Rectangle, triangle, trapezoid, circle, ellipse, annulus and sector use their textbook forms. Triangles from three sides use Heron's formula. Regular polygons use the standard side-squared constants: 1.720477 for a pentagon, 2.598076 for a hexagon, 4.828427 for an octagon.
• Conversion constants. Exact values only. 1 square yard is 9 square feet, 1 square foot is 0.09290304 square metres, 1 acre is 43,560 square feet, and 1 square foot is 144 square inches. The cubic yards divisor of 324 comes from 12 inches per foot multiplied by 27 cubic feet per cubic yard. Rounded constants such as 0.0929 are not used, because they drift by about 0.003 per cent.
• How the arithmetic is handled. Every calculation runs at full floating point precision and is rounded only for display. Rounding each room before adding it, which some calculators do, makes a whole home total drift by a few hundredths of a square foot.
• Verification. All twenty shape formulas and all nine unit conversions were checked against independent hand calculations before release. The worked example of 12 ft 6 in by 10 ft 3 in resolves to 128.13 square feet in this tool, in the Excel formulas in Section 8, in the R script in Section 9 and in the Python script in Section 10. Where the three genuinely disagree, such as Python's banker's rounding turning 128.125 into 128.12, the disagreement is named in Sections 8.4 and 10.4 rather than hidden.
• Rounding rules that are deliberate. Box counts always round up, never to nearest, because a part box does not finish a floor. Cost is calculated on the waste-included area, not the bare room area, because you pay for the offcuts.
• What it will not do. This tool reports a measured area from the numbers you type. It is not a measured survey and carries no legal standing for a sale, a mortgage valuation or a building permit. Section 16 lists every assumption and the direction of the error when each one fails.
• Evidence base. The accuracy and measurement-standard claims on this page are supported by the twenty peer-reviewed studies in Section 22, covering quantity-takeoff accuracy, floor-area measurement standards and the real-world discrepancies between them.

Maintained by Stats Unlock. Last reviewed 26 August 2026. Found an error? The formulas and the worked numbers are all on this page, so any result can be checked by hand.

More calculators from Stats Unlock.

Twenty peer-reviewed studies on area measurement, quantity takeoff and floor area accuracy, in APA 7th style. They are the evidence behind the accuracy and standards points made on this page.

1. Akanbi, T., Zhang, J., & Lee, Y.-C. (2023). IFC-based algorithms for automated quantity takeoff from architectural model: Case study on residential development project. Journal of Architectural Engineering, 29(4). View paper
2. Valinejadshoubi, M., Moselhi, O., Iordanova, I., Valdivieso, F., & Bagchi, A. (2024). Automated system for high-accuracy quantity takeoff using BIM. Automation in Construction, 157. View paper
3. Khosakitchalert, C., Yabuki, N., & Fukuda, T. (2019). Improving the accuracy of BIM-based quantity takeoff for compound elements. Automation in Construction, 106. View paper
4. Chen, B., Jiang, S., Qi, L., Su, Y., & Mao, Y. (2022). Design and implementation of quantity calculation method based on BIM data. Sustainability, 14(13). View paper
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