This grams to moles calculator converts between mass (grams), amount (moles) and number of particles (atoms or molecules) using the molar mass — in both directions. Enter what you have and the substance’s molar mass.
The Mole — Chemistry’s Counting Unit
Atoms are far too small to count individually, so chemistry counts them in bulk: one mole is exactly 6.02214076 × 10²³ particles (Avogadro’s number) — chosen so that one mole of a substance weighs its atomic/molecular mass in grams. The bridge between the balance and the atom-count is the molar mass, which our Molar Mass Calculator computes for any formula. This converter is part of our Chemistry Calculators collection.
The Three Conversions
- Grams → moles: moles = grams ÷ molar mass
- Moles → grams: grams = moles × molar mass
- Moles ⇄ particles: particles = moles × 6.022 × 10²³
Worked Example (Verified)
36 g of water (molar mass 18.015 g/mol):
- Moles: 36 ÷ 18.015 = 1.998 mol ≈ 2 mol — two shot-glasses of water hold two moles
- Molecules: 1.998 × 6.022 × 10²³ ≈ 1.20 × 10²⁴ molecules
- Reverse: 0.5 mol of NaCl (58.44 g/mol) weighs 29.22 g — set mode to “Moles” to verify.
Where This Conversion Leads
Grams ↔ moles is the first step of nearly every quantitative chemistry task: it opens Stoichiometry (reactions are balanced in moles, weighed in grams), solution concentrations (molarity is moles per liter), and gas calculations (a mole of any ideal gas occupies ~24.5 L at room conditions). Master this one conversion and the rest of the subject unlocks.
Related Tools
- Molar Mass Calculator — the g/mol for any formula
- Stoichiometry Calculator — reactions in moles
- Chemistry Calculators — the full collection
Frequently Asked Questions
How do I convert grams to moles?
Divide the mass by the substance’s molar mass: moles = g ÷ (g/mol). For 36 g of water: 36 ÷ 18.015 ≈ 2.00 mol.
How do I convert moles to grams?
Multiply moles by molar mass: 0.5 mol × 58.44 g/mol = 29.22 g for NaCl.
What is Avogadro’s number?
6.02214076 × 10²³ — the number of particles in one mole, now an exactly defined constant of the SI system.
How many molecules are in a mole of water?
6.022 × 10²³ molecules — and since each H₂O has 3 atoms, that is 1.807 × 10²⁴ atoms per mole of water.
Where do I get the molar mass?
Add up the atomic masses in the formula — or use our Molar Mass Calculator, which parses formulas like Ca(OH)₂ automatically.
Is this grams to moles calculator free?
Yes — free, instant, no sign-up.