Mole Calculator
Tell it what you know — mass, moles, or a particle count — and it fills in the other two using n = m ÷ M and Avogadro’s number.
Example: with What do you know? I know the mass (g) · Amount you know (grams) 25 · Substance (for molar mass) Water H2O (18.015 g/mol) · Custom molar mass (g/mol) 58.44 → Moles: 1.3877 mol.
Computed by the calculator below using its default values. Change any input to see your own numbers.
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Check it outHow to calculate moles
A mole is just a count — 6.022 × 10²³ particles — so every mole conversion runs through one of two constants. From mass to moles, divide by molar mass: 25 g of water ÷ 18.015 g/mol = 1.388 mol. From moles back to grams, multiply: 0.25 mol of glucose × 180.156 g/mol = 45.04 g.
From molecules to moles, divide the particle count by Avogadro’s number: 3.011 × 10²³ molecules ÷ 6.022 × 10²³ = 0.5 mol. Multiply by it to go the other way. Keeping the triangle straight — grams ↔ moles ↔ particles, with molar mass on one leg and Avogadro’s number on the other — is most of stoichiometry.
How it’s calculated
Moles n = mass ÷ molar mass (n = m ÷ M) when you know the mass; n = particles ÷ 6.02214076 × 10²³ (the exact SI Avogadro constant) when you know a particle count. The other two quantities are then mass = n × M and particles = n × 6.02214076 × 10²³. Built-in molar masses use IUPAC standard atomic weights (H2O 18.015, CO2 44.01, NaCl 58.44, NaOH 40.00, H2SO4 98.079, C6H12O6 180.156 g/mol).
Results update as you type and are estimates, not professional advice — verify important decisions with a qualified professional.
Common mistakes
- Confusing moles with molar mass — n counts amount (mol); M is grams per mole (g/mol).
- Multiplying by Avogadro's number when going from particles to moles — divide instead: particles ÷ 6.022 × 10²³.
- Rounding molar masses too early — use 18.015 g/mol for water, not 18, before scaling to large masses.
Frequently asked questions
How do I calculate moles from grams?
Divide the mass by the molar mass: n = m ÷ M. For 20 g of NaOH (40.00 g/mol), 20 ÷ 40 = 0.5 mol.
How do I convert molecules to moles?
Divide the number of molecules by Avogadro's number, 6.022 × 10²³. So 1.204 × 10²⁴ molecules is 1.204 × 10²⁴ ÷ 6.022 × 10²³ = 2 mol.
How do I convert moles to grams?
Multiply moles by molar mass: m = n × M. A quarter mole of glucose is 0.25 × 180.156 = 45.04 g.
What exactly is a mole?
A counting unit, like a dozen but enormous: exactly 6.02214076 × 10²³ particles. It links atom-scale masses to gram-scale lab measurements.
How many particles are in 2 moles?
Multiply by Avogadro's number: 2 × 6.022 × 10²³ = 1.204 × 10²⁴ particles, whether they are atoms, molecules, or ions.