Grams to Moles Calculator with Steps | StatsUnlock

A grams to moles calculator divides the mass of a substance by its molar mass. For 25.0 g of water, the molar mass of H₂O is 2 × 1.008 + 15.999 = 18.015 g/mol, so:

Rule of thumb: grams to moles, divide by M; moles to grams, multiply by M. Keep the answer to the significant figures of the mass you measured: 25.0 g has 3, so the answer is 1.39 mol.

A grams to moles calculator converts a mass you can weigh on a balance into an amount of substance, measured in moles (mol). One mole is exactly 6.022 140 76 × 10²³ particles. Since the 2019 redefinition of the SI, this number, Avogadro’s constant, is fixed by definition (Marquardt et al., 2018; Newell et al., 2018).

The bridge between grams and moles is the molar mass (M, in g/mol): the mass of one mole. You find it by adding the atomic weights of every atom in the formula. Then:

A worked one-liner: how many moles are in 10.0 g of sodium chloride? M(NaCl) = 22.990 + 35.45 = 58.44 g/mol, so n = 10.0 ÷ 58.44 = 0.171 mol.

Who uses it: CBSE and ICSE students meet the mole concept in NCERT Class 9 and Class 11; JEE and NEET papers use it in almost every physical chemistry question; IGCSE, GCSE, A level, AP Chemistry and IB students use it for every reacting-mass calculation. Pharmacists convert milligrams of a drug to millimoles, lab technicians weigh out reagents for a given number of moles, and teachers build answer keys for a grams to moles calculations worksheet.

Students often say “the moles” as if a mole were a thing. It is a unit, like a dozen: 1.39 mol of water is the amount, and mol is its unit (Pekdağ & Azizoğlu, 2013; Furió et al., 2002).

How accurate is this grams to moles calculator?

Molar masses use the CIAAW 2024 standard atomic weights for all 118 elements (Prohaska et al., 2022), or rounded exam values if you choose them. The calculator keeps full precision in every step and only rounds the final answer, to the significant figures of the number you typed. It then substitutes the answer back: n × M must give the mass, N ÷ N_A must give the moles, and the element masses must add up to the total. Only then does it show the Verified badge. The R and Python scripts in Sections 10 and 11 give the same 18.015 g/mol and 1.39 mol for the headline example.

4.1 What a number of moles actually means

A mole is a counting unit, like a dozen, but for particles too small to count one by one. 1.39 mol of water means 1.39 × 6.022 × 10²³ = 8.36 × 10²³ water molecules. Chemists weigh instead of count because a balance is fast and accurate, and the molar mass turns grams into a count.

4.2 Why heavy formulas give fewer moles per gram

Moles per gram is 1 ÷ M. Hydrogen gas (M = 2.016 g/mol) gives 0.496 mol per gram; gold (M = 196.97 g/mol) gives only 0.00508 mol per gram. The same 1.00 g of the two holds about 98 times more H₂ molecules than gold atoms. Chart 4 in the results shows this for your own mass.

4.3 Is your answer a sensible size?

If a school problem gives you 10⁴ mol or 10⁻⁹ mol, check the units first: a mass in mg typed as g is a factor of 1000 out.

4.4 Molecules, formula units, atoms and ions

The calculator names the particle for you. Covalent substances such as H₂O and CO₂ are made of molecules. Ionic compounds such as NaCl and CaCO₃ have no separate molecules, so one “particle” is a formula unit. A single element written as one symbol (Au, Fe, C) counts atoms. An ion such as SO₄²⁻ counts ions. Always state which particle you mean: 1 mol of O₂ is 6.022 × 10²³ molecules but 1.204 × 10²⁴ oxygen atoms.

4.5 Significant figures: why 1.39 and not 1.3877

Your answer can only be as precise as your weakest measurement. A mass of 25.0 g has three significant figures; the molar mass 18.015 g/mol has five; Avogadro’s constant is exact. The mass limits the answer to three, so 1.38773… mol is written 1.39 mol. The calculator keeps every digit until the last step, so rounding never builds up. Type 25.00 if your balance reads to 0.01 g, and you get 1.388 mol.

4.6 Which atomic weights you use changes the last digit

With CIAAW 2024 weights, M(H₂O) = 18.015 g/mol; with rounded exam values (H = 1, O = 16), M = 18 g/mol. For 25.0 g that gives 1.3877 and 1.3889 mol, both 1.39 mol to three significant figures. The difference shows up for heavy molecules or when you need four or more figures, so use the values your exam or lab manual gives.

4.7 The gas volume and molarity lines

The results table also shows the volume your moles would fill as an ideal gas, and the molarity if you dissolved them in a volume you type. The gas line is a reference only: water is a liquid at room temperature, so 1.39 mol of liquid water fills 25 mL, not 31.5 L. State which STP you use, because 0 °C and 1 bar (22.711 L/mol) and 0 °C and 1 atm (22.414 L/mol) differ by 1.3%.

4.8 A field note on why the molar mass step deserves the most care

In checking hundreds of student answers, nearly every wrong grams to moles result traces back to the molar mass, not the division. The usual culprits are a missed bracket (Ca(OH)₂ has two O atoms, not one), forgotten water of crystallisation in a hydrate, and Co typed for CO. Research on the mole concept finds the same thing: students can run the formula n = m ÷ M but struggle to link molar mass to what is in the formula (Staver & Lumpe, 1995; Furió et al., 2002). That is why this calculator writes the molar mass out element by element before it divides.

4.9 How this links to the next topic

Grams to moles is step one of stoichiometry. With moles in hand you use the mole ratio from a balanced equation to find the moles of a product, then multiply by its molar mass to get grams. The same n = m ÷ M runs through limiting reagent, theoretical yield, percent yield, empirical formula and molarity calculations.

▶ Convert a problem above to fill all five cards with your own answer.

This flowchart shows how to calculate moles from grams, on the same example used in the Excel, R, Python and by-hand sections: how many moles are in 25.0 g of water?

Check any box yourself: the Excel sheet in Section 9, the R script in Section 10 and the Python script in Section 11 all return 18.015 g/mol and 1.39 mol for this problem.

1. Choose what you want to find. Pick grams to moles, moles to grams, grams to atoms or molecules, atoms or molecules to grams, or find the molar mass.
2. Type the chemical formula. Write it as H2O, NaCl or Ca(OH)2, or tap a common compound. No formula? Leave it empty and type the molar mass in g/mol instead.
3. Check the capital letters. Element symbols start with a capital and any second letter is small: Co is cobalt, CO is carbon monoxide.
4. Enter the mass or the moles. Type the number exactly as measured, including trailing zeros such as 25.0, because they set the significant figures.
5. Pick the unit. Choose g, mg, µg, kg, lb or oz for mass, and mol, mmol or µmol for amount. The calculator converts for you.
6. Choose the atomic weights and purity. Keep CIAAW 2024 values or switch to rounded exam values, and type a purity such as 98% for an impure sample.
7. Press Convert. Nothing is calculated before you press it, and changing any input clears the old answer.
8. Read the answer and the molar mass table. The Verified badge means the answer was substituted back and matched.
9. Follow the steps and the mole map. Copy the working into your notebook in the same order.
10. Copy, share or batch. Copy the answer, share a link to the problem, download a report, or convert a whole worksheet on the Batch tab.

Excel cannot read a chemical formula, so you lay the formula out as a small table: one row per element with its count and atomic weight. SUMPRODUCT gives the molar mass, and a single division gives the moles. The sheet below uses the headline problem, 25.0 g of water, so it must return 18.015 g/mol and 1.39 mol, the same as the grams to moles calculator above.

9.1 The functions you need

9.2 Step by step

9.3 Awkward cases

• Brackets. Count the atoms before typing: Ca(OH)₂ is 1 Ca, 2 O, 2 H.
• Hydrates. Add the water as extra rows: CuSO₄·5H₂O has 9 O and 10 H.
• Very large or small numbers. Format the cell as Scientific with 2 decimals to see 8.36E+23.
• Moles to grams. Use =moles*molar_mass; the table layout is the same.

9.4 Why your Excel answer might differ from R, Python or this page

9.5 Charting in Excel

1. Select the element symbols and their subtotals (A2:A3, D2:D3).
2. Insert → Charts → Bar to show which element carries most of the molar mass (Chart 1 above).
3. For mass against moles, make a column of moles (0, 0.5, 1, 1.5, 2), a column =moles*$D$4, then Insert → Scatter with Straight Lines.

9.6 Excel errors you will probably hit

This base R script reads a formula, works out the molar mass element by element (brackets and hydrates included), converts grams to moles, molecules and atoms, checks the answer by substituting back, and saves one 300 dpi chart. For 25.0 g of water it prints 18.015 g/mol and 1.39 mol, matching the grams to moles calculator on this page.

10.1 The complete script

R, base only, saves grams_to_moles.png

# ============================================================
# Grams to moles in R: molar mass from the formula, then n = m / M
# StatsUnlock - https://statsunlock.com/grams-to-moles-calculator/
# Base R only. No packages to install.
# ============================================================

# ---- 1. Your problem -------------------------------------------
formula  <- "H2O"     # brackets and hydrates work: Ca(OH)2, CuSO4.5H2O
mass_g   <- 25.0      # grams (convert mg to g first: 325 mg = 0.325 g)
sig_figs <- 3         # significant figures in your mass

N_A <- 6.02214076e23  # Avogadro constant, mol^-1 (exact)
# CIAAW 2024 standard atomic weights (g/mol); add any element you need
W <- c(H = 1.008, Li = 6.94, C = 12.011, N = 14.007, O = 15.999, F = 18.998,
       Na = 22.990, Mg = 24.305, Al = 26.982, Si = 28.085, P = 30.974,
       S = 32.06, Cl = 35.45, K = 39.098, Ca = 40.078, Mn = 54.938,
       Fe = 55.845, Cu = 63.546, Zn = 65.38, Br = 79.904, Ag = 107.87,
       I = 126.90, Ba = 137.33, Au = 196.97, Pb = 207.2)

# Count atoms, multiplying through brackets and the hydrate dot
parse_formula <- function(f) {
  total <- c()
  parts <- strsplit(f, "[.*]")[[1]]
  for (i in seq_along(parts)) {
    part <- parts[i]; mult <- 1
    if (i > 1 && grepl("^[0-9]+", part)) {
      mult <- as.numeric(sub("^([0-9]+).*", "\\1", part))
      part <- sub("^[0-9]+", "", part)
    }
    tok <- regmatches(part, gregexpr("[A-Z][a-z]?|[0-9]+|[][()]", part))[[1]]
    stack <- list(numeric(0)); j <- 1
    while (j <= length(tok)) {
      t <- tok[j]; j <- j + 1
      if (t %in% c("(", "[")) { stack[[length(stack) + 1]] <- numeric(0); next }
      n <- 1
      if (j <= length(tok) && grepl("^[0-9]+$", tok[j])) { n <- as.numeric(tok[j]); j <- j + 1 }
      top <- length(stack)
      if (t %in% c(")", "]")) {
        inner <- stack[[top]] * n; stack[[top]] <- NULL; top <- top - 1
        for (k in names(inner)) stack[[top]][k] <- sum(stack[[top]][k], inner[k], na.rm = TRUE)
      } else {
        stack[[top]][t] <- sum(stack[[top]][t], n, na.rm = TRUE)
      }
    }
    for (k in names(stack[[1]])) total[k] <- sum(total[k], stack[[1]][k] * mult, na.rm = TRUE)
  }
  total
}

# ---- 2. Molar mass ---------------------------------------------
counts <- parse_formula(formula)
if (any(!names(counts) %in% names(W))) stop("Add the atomic weight of ", paste(setdiff(names(counts), names(W)), collapse = ", "))
sub_mass <- counts * W[names(counts)]
M <- sum(sub_mass)
print(data.frame(element = names(counts), atoms = as.vector(counts),
                 subtotal = round(as.vector(sub_mass), 3),
                 percent = round(100 * as.vector(sub_mass) / M, 2)))
cat(sprintf("Molar mass M(%s) = %.3f g/mol\n", formula, M))

# ---- 3. Grams to moles, moles to particles ---------------------
if (mass_g <= 0) stop("Mass must be greater than zero")
n <- mass_g / M
N <- n * N_A
cat(sprintf("Moles     n = m / M = %g g / %.3f g/mol = %s mol\n", mass_g, M, signif(n, sig_figs)))
cat(sprintf("Particles N = n x N_A = %s\n", format(signif(N, sig_figs), scientific = TRUE)))
cat(sprintf("Atoms in total = %s\n", format(signif(N * sum(counts), sig_figs), scientific = TRUE)))

# ---- 4. Verify: substitute back ---------------------------------
stopifnot(abs(n * M - mass_g) < 1e-9 * mass_g)
cat("Verdict: Verified, n x M gives back", round(n * M, 6), "g\n")

# ---- 5. One 300 dpi figure: moles of each element's atoms --------
png("grams_to_moles.png", width = 2100, height = 1350, res = 300)
par(mar = c(4.5, 5, 3, 1))
barplot(n * counts, names.arg = names(counts), las = 1, border = NA,
        col = c("#2563eb", "#ea580c", "#16a34a", "#9333ea", "#0d9488")[seq_along(counts)],
        xlab = "Element", ylab = "Moles of atoms (mol)",
        main = sprintf("%g g of %s = %s mol", mass_g, formula, signif(n, sig_figs)))
invisible(dev.off())
cat("Saved grams_to_moles.png\n")

Output: Molar mass M(H2O) = 18.015 g/mol, n = m / M = 25 g / 18.015 g/mol = 1.39 mol, Particles N = 8.36e+23, Verdict: Verified.

10.2 R traps

• signif() rounds to significant figures; round() rounds to decimal places. Use signif(n, 3) for 1.39.
• R prints 25.0 as 25, dropping the trailing zero. Keep track of significant figures yourself with sig_figs.
• log() is the natural log; use log10() if you build your own s.f. rounding.
• Named vectors must match: W[names(counts)] picks the right weight for each element.

10.3 What each part does

10.4 Using a package for element data

The script carries a small table of CIAAW atomic weights. To cover every element, the PeriodicTable package gives mass("O"); check that its values match the edition your course uses.

10.5 The figure

The script saves grams_to_moles.png at 2100 × 1350 pixels and 300 dpi: one bar per element showing the moles of its atoms in your sample (2.78 mol of H atoms and 1.39 mol of O atoms for 25.0 g of water).

This script does the same job in plain Python: it parses the formula, prints the molar mass table, converts grams to moles, molecules and atoms, verifies the answer and saves a 300 dpi chart. It is the same method the grams to moles calculator runs in your browser.

Install once: pip install matplotlib

11.1 The complete script

Python, saves grams_to_moles.png

# ============================================================
# Grams to moles in Python: molar mass from the formula, then n = m / M
# StatsUnlock - https://statsunlock.com/grams-to-moles-calculator/
# pip install matplotlib
# ============================================================
import re
import matplotlib
matplotlib.use("Agg")
import matplotlib.pyplot as plt

# ---- 1. Your problem -------------------------------------------
formula = "H2O"        # brackets and hydrates work: Ca(OH)2, CuSO4.5H2O
mass_g = 25.0          # grams (convert mg to g first: 325 mg = 0.325 g)
sig_figs = 3           # the number of significant figures in your mass

N_A = 6.02214076e23    # Avogadro constant, mol^-1 (exact)
# CIAAW 2024 standard atomic weights (g/mol); add any element you need
W = {"H": 1.008, "Li": 6.94, "C": 12.011, "N": 14.007, "O": 15.999, "F": 18.998,
     "Na": 22.990, "Mg": 24.305, "Al": 26.982, "Si": 28.085, "P": 30.974,
     "S": 32.06, "Cl": 35.45, "K": 39.098, "Ca": 40.078, "Mn": 54.938,
     "Fe": 55.845, "Cu": 63.546, "Zn": 65.38, "Br": 79.904, "Ag": 107.87,
     "I": 126.90, "Ba": 137.33, "Au": 196.97, "Pb": 207.2}

def parse_formula(f):
    """Count atoms in a formula such as Ca(OH)2, Al2(SO4)3 or CuSO4.5H2O."""
    total = {}
    for i, part in enumerate(re.split(r"[.*·]", f)):
        mult = 1
        m = re.match(r"^(\d+)(.*)$", part)
        if m and i > 0:                        # the 5 in CuSO4.5H2O
            mult, part = int(m.group(1)), m.group(2)
        tokens = re.findall(r"[A-Z][a-z]?|\d+|[()\[\]]", part)
        stack, j = [{}], 0
        while j < len(tokens):
            t = tokens[j]; j += 1
            if t in "([":
                stack.append({}); continue
            n = 1
            if j < len(tokens) and tokens[j].isdigit():
                n = int(tokens[j]); j += 1
            if t in ")]":                      # close a bracket, multiply what is inside
                for k, v in stack.pop().items():
                    stack[-1][k] = stack[-1].get(k, 0) + v * n
            else:                              # an element symbol
                stack[-1][t] = stack[-1].get(t, 0) + n
        for k, v in stack[0].items():
            total[k] = total.get(k, 0) + v * mult
    return total

# ---- 2. Molar mass ---------------------------------------------
counts = parse_formula(formula)
missing = [e for e in counts if e not in W]
if missing:
    raise SystemExit(f"Add the atomic weight of {missing} to W")
M = sum(n * W[e] for e, n in counts.items())
for e, n in counts.items():
    print(f"  {e}: {n} x {W[e]} = {n * W[e]:.3f} g/mol ({100 * n * W[e] / M:.2f}%)")
print(f"Molar mass M({formula}) = {M:.3f} g/mol")

# ---- 3. Grams to moles, moles to particles ---------------------
if mass_g <= 0:
    raise SystemExit("Mass must be greater than zero")
n = mass_g / M
N = n * N_A
atoms = N * sum(counts.values())
print(f"Moles     n = m / M = {mass_g} g / {M:.3f} g/mol = {n:.{sig_figs}g} mol")
print(f"Particles N = n x N_A = {N:.{sig_figs - 1}e}")
print(f"Atoms in total = {atoms:.{sig_figs - 1}e}")

# ---- 4. Verify: substitute back ---------------------------------
assert abs(n * M - mass_g) < 1e-9 * mass_g, "n x M does not give back the mass"
print("Verdict: Verified, n x M gives back", round(n * M, 6), "g")

# ---- 5. One 300 dpi figure: moles of each element's atoms --------
els = list(counts)
mol_atoms = [n * counts[e] for e in els]
fig, ax = plt.subplots(figsize=(7, 4.5))
ax.bar(els, mol_atoms, color=["#2563eb", "#ea580c", "#16a34a", "#9333ea", "#0d9488"][:len(els)])
ax.set_xlabel("Element")
ax.set_ylabel("Moles of atoms in the sample (mol)")
ax.set_title(f"{mass_g} g of {formula} = {n:.{sig_figs}g} mol")
fig.tight_layout()
fig.savefig("grams_to_moles.png", dpi=300)
print("Saved grams_to_moles.png")

Output: Molar mass M(H2O) = 18.015 g/mol, n = m / M = 25.0 g / 18.015 g/mol = 1.39 mol, Particles N = 8.36e+23, Atoms in total = 2.51e+24.

11.2 Python traps

• 6.02214076e23 is how Python writes 6.022 × 10²³; 6.022*10^23 is wrong because ^ is bitwise XOR.
• f"{n:.3g}" rounds to 3 significant figures; round(n, 3) rounds to 3 decimal places.
• round() rounds half to even, so round(0.125, 2) gives 0.12. For exam-style rounding use the decimal module.
• The periodictable and mendeleev packages may differ from CIAAW 2024 in the last digit for some elements.

11.3 Using a package

With pip install periodictable, periodictable.formula("H2O").mass returns the molar mass for any formula, and 25.0 / periodictable.formula("H2O").mass gives the moles.

11.4 What each part does

11.5 The figure

The script saves grams_to_moles.png at 300 dpi with the moles of each element’s atoms in the sample.

12.1 Atomic weights of common elements

Source: CIAAW (IUPAC Commission on Isotopic Abundances and Atomic Weights), abridged standard atomic weights, 2024 edition. Dimensionless; the same number in g/mol is the molar mass of the atoms.

12.2 Molar masses of common compounds, and moles in 1 g and 10 g

Each row was computed by the same engine as the grams to moles calculator. Use it to check homework fast.

12.3 Mass and amount units

12.4 Molar volume of an ideal gas at different reference conditions

V_m = RT ÷ P with R = 8.314 462 618 J mol⁻¹ K⁻¹ (exact). CBSE and older textbooks use 22.4 L at 0 °C and 1 atm; IUPAC STP since 1982 is 0 °C and 1 bar. Valid only for gases that behave ideally.

12.5 Significant figure rules for grams to moles

12.6 Grams to moles practice: 25 worked conversions with answers

A grams to moles calculations worksheet with its answer key, every line checked by the calculator engine. Cover the last two columns and try them first.

Eight examples run through the grams to moles calculator, from a textbook question to a trap that costs marks. Each figure is drawn from the computed numbers: the bar lengths are the moles of each element’s atoms in the sample.

This is the written method examiners expect, on the same example as Sections 7, 9, 10 and 11: how many moles are there in 25.0 g of water?

14.1 The written method

1. Write the formula and count the atoms. H₂O: 2 hydrogen, 1 oxygen.
2. Write the molar mass sum. M = 2 × 1.008 + 1 × 15.999 = 18.015 g/mol (or 2 × 1 + 16 = 18 g/mol with exam values).
3. Make sure the mass is in grams. 25.0 g. (325 mg would be 0.325 g.)
4. Write the formula. n = m ÷ M.
5. Substitute with units. n = 25.0 g ÷ 18.015 g/mol. The grams cancel, leaving mol.
6. Calculate. n = 1.387 732… mol.
7. Round once, at the end. 25.0 has 3 significant figures, so n = 1.39 mol.
8. Check. 1.39 × 18.015 = 25.0 g. The answer is sensible: water is light, so 25 g is more than one mole.

For moles to grams, swap step 4 for m = n × M. For grams to molecules, add N = n × 6.022 × 10²³.

14.2 On a scientific calculator

On a Casio fx-991EX or fx-82MS: type 2 × 1.008 + 15.999 = to get 18.015. Then 25 ÷ Ans = gives 1.387732…. For molecules, × 6.022 ×10^x 23 = gives 8.357 × 10²³.

Use the ×10^x (or EXP) key, never × 10 ^ 23 typed by hand: dividing by 6.022 × 10 ^ 23 without brackets divides by 6.022 and multiplies by 10²³. Key names differ between models; check your manual.

14.3 Do it in the lab: water of crystallisation in copper(II) sulfate

Example data. x = 0.0500 ÷ 0.0100 = 4.98, so x = 5: the formula is CuSO₄·5H₂O. The water mass (0.90 g) has only two significant figures, which limits x to about ±0.1.

14.4 Grams to moles practice problems with answers

Ten practice problems, easy to hard. Open each one to see the answer.

14.5 Mistakes that lose marks

Studies of how students handle the mole find the same slips again and again: treating the mole as a mass, losing track of which particle is being counted, and mixing up molar mass with mass (Gabel & Sherwood, 1984; Krishnan & Howe, 1994; Pekdağ & Azizoğlu, 2013).

• Multiplying by the molar mass when you should divide (grams to moles is m ÷ M).
• Missing atoms inside brackets: Ca(OH)₂ is 74.092 g/mol, not 57.085.
• Leaving out the water in a hydrate: CuSO₄·5H₂O is 249.677 g/mol, not 159.602.
• Using 16 g/mol for oxygen gas instead of 32 g/mol for O₂.
• Forgetting to convert mg to g, giving an answer 1000 times too big.
• Rounding the molar mass to 2 figures before dividing.
• Writing “mols” or leaving out the unit altogether.

Four real examples

Decision tree

1. Do you have a mass of a pure substance? Yes: grams to moles (this calculator). No: go on.
2. Do you have a concentration and a volume? Yes: n = c × V. No: go on.
3. Do you have a gas volume, temperature and pressure? Yes: PV = nRT, or V ÷ V_m at a stated STP.
4. Do you have a number of particles? Yes: n = N ÷ N_A (the particles mode here).

Limitations. A grams to moles calculator turns mass into amount, but it cannot tell you whether the mass belongs to the substance you think it does. Molar masses of ions ignore the electron mass (under 0.003% for most ions). For elements with no standard atomic weight, such as Tc, the mass number of the longest-lived isotope is used and a note appears.

What the answer is

A grams to moles calculator divides a mass by a molar mass. For the headline problem, 25.0 g of water ÷ 18.015 g/mol = 1.39 mol, which is 8.36 × 10²³ molecules and 2.51 × 10²⁴ atoms.

What it means chemically

Moles count particles. Chemical equations, concentrations and gas laws all work in moles, not grams, so converting grams to moles is how a mass on a balance becomes something chemistry can use.

Watch out for

Get the molar mass right first: brackets, hydrates and capital letters cause most wrong answers. Convert mg to g, divide rather than multiply, and round only once, to the significant figures of the mass.

Next steps

Use your moles with the mole ratio from a balanced equation to find a product mass or the limiting reagent, or practise with the 25 worked conversions in Section 12 and the ten problems in Section 14. For every reacting-mass problem, the first step is the same: the grams to moles calculator.

Rearranging n = m ÷ M is algebra, and judging whether two measured amounts really differ is statistics; these tools cover both.

Peer-reviewed sources for the methods and data used in this grams to moles calculator: the definition of the mole, the Avogadro constant, standard atomic weights, and research on how students learn the mole concept and stoichiometry.

1. Andreas, B., Azuma, Y., Bartl, G., Becker, P., Bettin, H., Borys, M., ... Zakel, S. (2011). Determination of the Avogadro constant by counting the atoms in a ²⁸Si crystal. Physical Review Letters, 106(3), 030801. https://doi.org/10.1103/PhysRevLett.106.030801
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