Temperature Converter with Steps (Free) | StatsUnlock

A temperature converter uses °F = °C × 9/5 + 32, °C = (°F − 32) × 5/9 and K = °C + 273.15. So 37 °C = 37 × 1.8 + 32 = 98.6 °F = 310.15 K, and 300 K = 26.85 °C. A thermometer good to ±0.1 °C is good to ±0.18 °F.

Rule of thumb: double the Celsius and add 30 for a quick Fahrenheit estimate (20 °C ≈ 70 °F; exact 68 °F). For a temperature difference, leave out the 32: a 10 °C rise is an 18 °F rise.

Temperature scales differ in two ways: the size of one degree and where zero sits. A Celsius degree is 1.8 times a Fahrenheit degree, and 0 °C is 32 °F. Kelvin uses Celsius-sized degrees but starts at absolute zero, so K = °C + 273.15. Since 2019 the kelvin has been defined by fixing the Boltzmann constant (Stöck et al., 2019), and practical thermometers follow the International Temperature Scale of 1990 (Preston-Thomas, 1990). A temperature converter applies both the scale factor and the offset, exactly, in either direction.

A worked one-liner: °F = 37 × 9/5 + 32 = 66.6 + 32 = 98.6 °F; K = 37 + 273.15 = 310.15 K; °R (Rankine) = 310.15 × 1.8 = 558.27 °R.

Who uses it: students converting between Celsius, Fahrenheit and Kelvin in chemistry and physics; cooks converting oven temperatures and gas marks; parents and nurses reading thermometers; travelers checking the weather; engineers using Rankine; and lab staff converting thermometer tolerances. One page replaces separate °C to °F, °F to °C, Kelvin, oven and body-temperature converters.

Quick answers to the questions people ask most

4.1 What the result means

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4.2 The formula

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4.3 Uncertainty and ranges

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4.4 The detail that changes the answer

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4.5 What to do next

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4.6 Why 9/5 and 32?

Between the freezing and boiling points of water there are 100 Celsius degrees and 180 Fahrenheit degrees (32 to 212), so one Celsius degree equals 180 ÷ 100 = 1.8 = 9/5 Fahrenheit degrees. The scales also start at different places: 0 °C is 32 °F. Every conversion between two linear scales is therefore a multiply and an add. Kelvin keeps the Celsius degree size but moves zero to absolute zero, −273.15 °C, the point fixed exactly by the 2019 redefinition of the kelvin through the Boltzmann constant (Fischer et al., 2018; Machin, 2018).

4.7 Readings versus differences

A reading (it is 25 °C) needs the full formula with the offset. A difference (it warmed by 5 °C, the thermometer is accurate to ±0.2 °C, the oven runs 10 °C hot) needs only the factor: 5 °C = 9 °F = 5 K. Choosing the wrong one is the single most common temperature conversion error. In the calculator, set “This is a” to Difference for changes and ranges.

4.8 Kelvin in science

Gas laws, reaction rates and radiation all use absolute temperature. Doubling 10 °C to 20 °C does not double the thermal energy; going from 283.15 K to 293.15 K is a 3.5% increase. Always convert to kelvin before using PV = nRT, the Arrhenius equation or the Stefan-Boltzmann law, and write “K”, not “°K”. Modern thermometry and its traceability are reviewed by Moldover et al. (2016).

A temperature in a report needs the number, the unit with its symbol (°C, °F, K), a space between them, and for measured values the uncertainty and, for body temperatures, the site. The seven write-ups below are filled from the temperature converter; they show the headline example until you press Convert.

Showing the headline example (37 °C to °F). Press Convert above to fill all seven write-ups with your own result.

5.1 Style rules

5.2 Seven ready-to-copy write-ups

The same worked problem as Sections 0, 9, 10, 11 and 14: convert 37 °C (thermometer ±0.1 °C) to Fahrenheit and Kelvin.

1. Pick what you want to do. Choose a mode in Section 2: convert a temperature, build a conversion chart, convert an oven temperature or gas mark, or compare body temperature sites.
2. Load a sample or type your value. Twelve worked problems are in the sample menu. Sample 1 is the headline problem. Nothing is calculated until you press Convert.
3. Choose the from and to scales. Celsius, Fahrenheit, Kelvin, Rankine, Réaumur, Rømer, Newton or Delisle. Use Swap to reverse them.
4. Say whether it is a reading or a difference. A reading (it is 25 °C) uses the offset; a difference (it rose 5 °C, ± 0.2 °C) does not.
5. Add the thermometer accuracy. Optional: the ± tolerance is converted by the degree size, so ± 0.1 °C becomes ± 0.18 °F.
6. Set decimal places. Auto shows the exact result trimmed of binary noise, or choose 0 to 4 decimals.
7. Press Convert Temperature. Press the button or Enter. The answer on every scale, a Verified badge, the formula and every step appear in Section 3.
8. Read the figure and charts. The thermometer figure and four charts show the scales side by side, the conversion line, landmarks and degree sizes.
9. Copy the write-up. Section 5 fills seven ready texts for a report, a log, code, an exam, chat, a results paragraph and a table.
10. Print a chart or run a batch. Download Doc or PDF, build a printable table in chart mode, or convert a whole column in the Batch tab.

Excel has a built-in CONVERT function for temperature, and the formulas are short enough to type by hand. The sheet repeats the headline problem (37 °C ± 0.1 °C), so the numbers match Sections 0, 7, 10, 11 and 14.

9.1 The formulas you need

9.2 Step by step

9.3 A printable chart

Put 0 in A2 and =A2+10 in A3, fill down to 220. In B2 type =ROUND((A2-32)*5/9,1) and fill down. Print the two columns as a °F to °C chart.

9.4 Why Excel may differ from R or Python

9.5 Charting

Select the °C and °F columns and insert a Scatter chart with straight lines. The line has slope 1.8 and crosses the line °F = °C at −40.

9.6 Errors you may see

• #N/A: a CONVERT unit code in the wrong case, such as "c".
• #VALUE!: a degree sign typed into a number cell ("37 °C").
• A temperature that looks 32 too high: + 32 was added to a difference.

A complete, copy-and-run script that reproduces the temperature converter for the headline problem. It converts 37 °C to every main scale, converts the thermometer tolerance and a temperature difference correctly (without the offset), prints a °F to °C chart and saves one 300 dpi figure.

10.1 The complete script

R, base only, saves celsius_fahrenheit.png

# Temperature conversion: all scales, a tolerance, a difference and a printable chart
# StatsUnlock - https://statsunlock.com/temperature-converter/   Base R only.

to_c   <- list(C = function(x) x, F = function(x) (x - 32) * 5 / 9, K = function(x) x - 273.15, R = function(x) x * 5 / 9 - 273.15)
from_c <- list(C = function(c) c, F = function(c) c * 9 / 5 + 32, K = function(c) c + 273.15, R = function(c) (c + 273.15) * 9 / 5)
convert <- function(x, from, to) {
  c <- to_c[[from]](x)
  if (any(c < -273.15)) stop("below absolute zero")
  round(from_c[[to]](c), 10)                   # round away binary noise
}

# ---- 1. Headline: 37 C with a +/-0.1 C thermometer ----
t <- 37; tol <- 0.1
cat(sprintf("%g C = %g F = %g K = %g R\n", t, convert(t, "C", "F"), convert(t, "C", "K"), convert(t, "C", "R")))
cat(sprintf("Tolerance +/-%g C = +/-%.2f F (a difference: no + 32)\n", tol, tol * 9 / 5))
cat(sprintf("98.6 F = %g C; 300 K = %g C; 573 K = %g C\n", convert(98.6, "F", "C"), convert(300, "K", "C"), convert(573, "K", "C")))
stopifnot(convert(convert(t, "C", "F"), "F", "C") == t)

# ---- 2. Difference and crossover ----
cat(sprintf("A 10 C rise = %g F rise = 10 K rise\n", 10 * 9 / 5))
cat("C equals F at -40 ->", convert(-40, "C", "F"), "\n")

# ---- 3. Printable F to C chart ----
f <- seq(0, 220, by = 20)
print(data.frame(F = f, C = round(convert(f, "F", "C"), 2)), row.names = FALSE)

# ---- 4. One 300 dpi figure ----
cc <- seq(-60, 120, by = 1)
png("celsius_fahrenheit.png", width = 6, height = 4, units = "in", res = 300)
plot(cc, cc * 9 / 5 + 32, type = "l", lwd = 2.5, col = "#2563eb", xlab = "Celsius", ylab = "Fahrenheit")
abline(0, 1, lty = 2, col = "#94a3b8"); points(c(-40, 37), c(-40, 98.6), pch = 19, col = c("#9333ea", "#ea580c"))
invisible(dev.off())

10.2 Output

37 C = 98.6 F = 310.15 K = 558.27 R
Tolerance +/-0.1 C = +/-0.18 F (a difference: no + 32)
98.6 F = 37 C; 300 K = 26.85 C; 573 K = 299.85 C
A 10 C rise = 18 F rise = 10 K rise
C equals F at -40 -> -40 
   F      C
   0 -17.78
  20  -6.67
  40   4.44
  60  15.56
  80  26.67
 100  37.78
 120  48.89
 140  60.00
 160  71.11
 180  82.22
 200  93.33
 220 104.44

10.3 Traps

• The functions are vectorized: convert a whole column with one call.
• round() rounds half to even; format with sprintf for fixed decimals.
• Never add 32 to a difference or a tolerance.

10.4 What each part does

10.5 Adapting it

Change t for your temperature and the from and to codes (C, F, K, R). Pass a whole vector or list to convert a column of readings at once.

A complete, copy-and-run script that reproduces the temperature converter for the headline problem. It converts 37 °C to every main scale, converts the thermometer tolerance and a temperature difference correctly (without the offset), prints a °F to °C chart and saves one 300 dpi figure.

Install once: pip install numpy matplotlib

11.1 The complete script

Python with NumPy and Matplotlib, saves celsius_fahrenheit.png

# Temperature conversion: all scales, a tolerance, a difference, a printable chart and one figure
# StatsUnlock - https://statsunlock.com/temperature-converter/
import numpy as np
import matplotlib
matplotlib.use("Agg")
import matplotlib.pyplot as plt

# ---- 1. Exact definitions (via Celsius) ----
to_c = {"C": lambda x: x, "F": lambda x: (x - 32) * 5 / 9, "K": lambda x: x - 273.15, "R": lambda x: x * 5 / 9 - 273.15}
from_c = {"C": lambda c: c, "F": lambda c: c * 9 / 5 + 32, "K": lambda c: c + 273.15, "R": lambda c: (c + 273.15) * 9 / 5}

def convert(x, frm, to):
    c = to_c[frm](x)
    if c < -273.15:
        raise ValueError("below absolute zero")
    return round(from_c[to](c), 10)             # round away binary noise

# ---- 2. The headline: 37 C with a +/-0.1 C thermometer ----
t, tol = 37.0, 0.1
print(f"{t} C = {convert(t, 'C', 'F')} F = {convert(t, 'C', 'K')} K = {convert(t, 'C', 'R')} R")
print(f"Tolerance +/-{tol} C = +/-{tol * 9 / 5:.2f} F (a difference: no + 32)")
print(f"98.6 F = {convert(98.6, 'F', 'C')} C; 300 K = {convert(300, 'K', 'C')} C; 573 K = {convert(573, 'K', 'C')} C")
assert convert(convert(t, "C", "F"), "F", "C") == t

# ---- 3. A temperature difference ----
rise_c = 10
print(f"A {rise_c} C rise = {rise_c * 9 / 5:g} F rise = {rise_c} K rise")

# ---- 4. Crossover and a printable F to C chart ----
print("C equals F at", -40.0, "->", convert(-40, "C", "F"))
for f in range(0, 221, 20):
    print(f"{f:>4} F = {convert(f, 'F', 'C'):7.2f} C")

# ---- 5. One 300 dpi figure ----
c = np.linspace(-60, 120, 181)
fig, ax = plt.subplots(figsize=(6, 4))
ax.plot(c, c * 9 / 5 + 32, color="#2563eb", lw=2.5, label="F = C x 9/5 + 32")
ax.plot(c, c, color="#94a3b8", lw=1, ls="--", label="F = C")
ax.plot(-40, -40, "o", color="#9333ea", ms=9, label="crossover -40")
ax.plot(37, 98.6, "o", color="#ea580c", ms=9, label="37 C = 98.6 F")
ax.set_xlabel("Celsius"); ax.set_ylabel("Fahrenheit"); ax.legend(frameon=False)
fig.tight_layout(); fig.savefig("celsius_fahrenheit.png", dpi=300)

11.2 Output

37.0 C = 98.6 F = 310.15 K = 558.27 R
Tolerance +/-0.1 C = +/-0.18 F (a difference: no + 32)
98.6 F = 37.0 C; 300 K = 26.85 C; 573 K = 299.85 C
A 10 C rise = 18 F rise = 10 K rise
C equals F at -40.0 -> -40.0
   0 F =  -17.78 C
  20 F =   -6.67 C
  40 F =    4.44 C
  60 F =   15.56 C
  80 F =   26.67 C
 100 F =   37.78 C
 120 F =   48.89 C
 140 F =   60.00 C
 160 F =   71.11 C
 180 F =   82.22 C
 200 F =   93.33 C
 220 F =  104.44 C

11.3 Traps

• (98.6 - 32) * 5 / 9 gives 37.0 here, but other values can print with trailing binary digits; round(x, 10) removes them.
• Integer division: use / not //.
• Check for values below absolute zero before converting.

11.4 What each part does

11.5 Adapting it

Change t for your temperature and the from and to codes (C, F, K, R). Pass a whole vector or list to convert a column of readings at once.

12.1 Celsius to Fahrenheit chart

°F = °C × 9/5 + 32; K = °C + 273.15. Exact. Last checked: October 2026.

12.2 Fahrenheit to Celsius chart

°C = (°F − 32) × 5/9, rounded to 0.1 °C. Last checked: October 2026.

12.3 Landmark and ITS-90 fixed-point temperatures

Fixed points from the International Temperature Scale of 1990 (Preston-Thomas, 1990); on ITS-90 water boils at about 99.97 °C at 1 atm. Last checked: October 2026.

12.4 Oven temperatures and gas marks

UK gas mark table as printed on cookers and in recipe books; fan ovens about 20 °C lower. Check your oven with a thermometer. Last checked: October 2026.

12.5 Body temperature by site

Ranges from the systematic review of Sund-Levander et al. (2002); site differences from Niven et al. (2015) and Craig et al. (2002). General guidance, not medical advice. Last checked: October 2026.

12.6 The same temperature on eight scales

Historical scales by their modern definitions against Celsius. Last checked: October 2026.

Eight worked problems that cover what a temperature converter meets: a textbook kelvin question, weather, a gas law, a recipe, a home thermometer, a climate difference, the crossover and an impossible value. Each number was checked in Python.

The written method, calculator keys and a short ice-point check, for the headline problem: 37 °C to °F and K, with a thermometer accurate to ± 0.1 °C.

14.1 The written method

1. Reading or difference? 37 °C is a reading.
2. Multiply by 9/5. 37 × 1.8 = 66.6.
3. Add 32. 66.6 + 32 = 98.6 °F.
4. Kelvin. 37 + 273.15 = 310.15 K.
5. Tolerance. ± 0.1 × 1.8 = ± 0.18 °F (no + 32).
6. Check. (98.6 − 32) × 5/9 = 37 ✓

14.2 On a calculator

14.3 Lab SOP: ice-point check of a thermometer

14.4 Practice problems

14.5 Mistakes that lose marks

• Multiplying by 5/9 before subtracting 32.
• Adding 32 to a difference or tolerance.
• Writing °K.
• Using 273 instead of 273.15 when the answer needs it.
• Using °C in a gas law.
• Leaving out the unit.

14.6 Check-yourself and lab questions

The arithmetic is simple, so almost every error is about order, offsets or measurement site. The temperature converter guards against each one below.

The body temperature mode is a unit and site converter, not a diagnostic tool. Normal body temperature varies with age, sex, time of day and the person (Obermeyer et al., 2017; Geneva et al., 2019).

Your result

The temperature converter gives 37 °C = 98.6 °F. Use °F = °C × 9/5 + 32 and K = °C + 273.15, and convert differences without the offset.

What the temperature converter does

Temperature conversion is two numbers, a factor and an offset, but the mistakes happen in the order of operations, in differences, in kelvin and in where a body temperature was taken. This temperature converter covers eight scales, readings and differences, printable charts, oven settings and body-temperature sites, and shows every step.

Watch out for

• Subtract 32 before multiplying by 5/9.
• No offset for differences and tolerances.
• Kelvin for gas laws, with no degree sign.
• Fan ovens about 20 °C lower.
• Always note the body site.

Next steps

For repeated readings, use the mean calculator and standard deviation calculator. For density at a given temperature, the specific gravity calculator uses water density from 0 to 40 °C. Whatever the scale, start and finish with the temperature converter.

Use these to summarize repeated temperature readings and to work with temperature-dependent lab quantities.

Peer-reviewed sources behind this temperature converter: the International Temperature Scale of 1990, the 2019 redefinition of the kelvin and the Boltzmann constant, thermometry, body temperature by measurement site, fever thresholds and normal ranges, and uncertainty. Standards (SI Brochure 9th edition, ITS-90, ISO 80000-5) are named where they are used. Every DOI checked October 2026.

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