Grams to Moles Calculator

Converting grams to moles is the most common calculation in chemistry. The formula n = m/M divides the sample mass by the molar mass. This unlocks every stoichiometry and concentration calculation.

⚗️ Stoichiometry📐 n = m/M🧪 General Chemistry

Mass m (g)

Molar Mass M (g/mol)

Please enter valid values.

Formula & Reference

Variable	Symbol	Formula	Units
Moles	n	n = m/M	mol
Mass	m	m = n × M	g
Molar Mass	M	Sum of atomic masses	g/mol
Key Masses	H₂O	18.02 g/mol — 1 mol = 18.02 g	g/mol
Key Masses	NaCl	58.44 g/mol — 1 mol = 58.44 g	g/mol

Step-by-Step Examples

Example 1

Water

How many moles in 90.0 g of H₂O (M=18.02)?

n = 90.0 / 18.02
n = 4.995 mol

✓ 4.995 mol H₂O

Example 2

Sodium Chloride

36.50 g of NaCl (M=58.44 g/mol).

n = 36.50 / 58.44 = 0.6245 mol

✓ 0.6245 mol NaCl

Example 3

Glucose

450 g of glucose C₆H₁₂O₆ (M=180.16 g/mol).

n = 450 / 180.16 = 2.498 mol

✓ 2.498 mol glucose

Real-World Applications

🧪

Lab Reagent Prep

Every reagent preparation starts with converting the required mass to moles.

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Pharmacy

Converting drug mass to moles ensures accurate molar dosing.

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Chemical Engineering

Reactor design requires mole quantities for stoichiometric feed ratios.

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Exam Prep

Grams-to-moles is tested on every chemistry exam from high school to university.

Common Mistakes to Avoid

⚠️

Using wrong molar mass

Look up or calculate M precisely. Water is 18.015 g/mol, not 18. For NaCl: 22.990 + 35.453 = 58.443 g/mol.

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Wrong units for mass

Mass must be in grams. If given in kg or mg, convert first: 1 kg = 1000 g, 1 mg = 0.001 g.

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Inverting the formula

n = m/M not m/n. Divide mass by molar mass. If your answer in moles is larger than the mass in grams for common compounds, recheck.

Frequently Asked Questions

What molar masses should I memorize? ▾

H₂O=18.02, NaCl=58.44, CO₂=44.01, H₂SO₄=98.08, NaOH=40.00, HCl=36.46, CaCO₃=100.09, NH₃=17.03, C₆H₁₂O₆=180.16.

How many moles is 1 gram of hydrogen? ▾

M(H₂)=2.016 g/mol. n = 1/2.016 = 0.496 mol. But 1 g of H atoms: M(H)=1.008, n = 0.992 mol.

What if I only know the formula, not the molar mass? ▾

Use our Molar Mass Calculator to find M from the formula, then divide your mass by that M.

How precise should my answer be? ▾

Match significant figures of the given data. If mass is 36.0 g (3 sig figs) and M is 18.02 (4 sig figs), give answer to 3 sig figs: 2.00 mol.

Can I convert moles back to grams? ▾

Yes: m = n × M. If you have 0.500 mol NaCl: m = 0.500 × 58.44 = 29.22 g.

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Formula Explorer connections

Interpretation: This relationship converts chemical amount, mass, composition or balanced-equation ratios into a reaction quantity. Assumption: Use a balanced reaction, consistent units and the correct molar mass. Purity, side reactions and limiting reagents can change experimental results.

Limiting Reagent Calculator →Mass Percent Calculator →Molar Mass Calculator →Chemistry Formula Explorer →