Grams to Moles Calculator

Type the mass in grams and the molar mass (g/mol) and get moles instantly. Or convert moles back to grams.

Example: 18.015 g H₂O

From periodic table / formula

mol = g ÷ (g/mol)

Reverse: Moles → Grams

Enter amount of substance

g = mol × molar mass

Current substance: Custom compound

Tip: if your result looks odd, double-check the molar mass. Most errors come from using the wrong g/mol.

Common examples

Substance Molar mass (g/mol) 10 g → mol 1 mol → g
Water (H₂O) 18.015 10 ÷ 18.015 ≈ 0.555 mol 18.015 g
NaCl 58.44 10 ÷ 58.44 ≈ 0.171 mol 58.44 g
Glucose (C₆H₁₂O₆) 180.16 10 ÷ 180.16 ≈ 0.0555 mol 180.16 g

How grams → moles works

The mole links the mass of a substance to the number of particles. To convert, you must know its molar mass in g/mol.

moles = mass (g) ÷ molar mass (g/mol)

Example: 36.03 g H₂O ÷ 18.015 g/mol = 2.000 mol H₂O

Where to get molar mass

From the chemical formula:

  • Write the formula: e.g. H₂O
  • Take atomic masses from the periodic table: H = 1.008, O = 16.00
  • Multiply and add: 2×1.008 + 16.00 = 18.016 ≈ 18.015 g/mol

Reverse: moles → grams

mass (g) = moles × molar mass (g/mol)

Example: 0.25 mol NaCl × 58.44 g/mol = 14.61 g NaCl

FAQ

1. Do I need Avogadro’s number?

Not for mass ↔ moles. Avogadro’s number is used when you want the number of molecules/atoms from moles.

2. What if I only know chemical name?

Look up its formula and molar mass, then enter it here.

3. Why is my answer different from class notes?

Teachers sometimes round molar masses (e.g. use 58.5 instead of 58.44). Use the same rounding to match their answer.