Science & Weather · Chemistry
Molar Mass Calculator — Molecular Weight, Composition & Grams ⇄ Moles
Type a chemical formula such as H2O, Ca(OH)2, K4[Fe(CN)6] or CuSO4·5H2O to get its molar mass (molecular weight) from IUPAC standard atomic weights, the mass percentage of each element, and conversions between grams, moles and number of molecules.
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Your inputs
Quick start — try a typical case
Case matters: Co is cobalt, CO is carbon monoxide. Use ( ) or [ ] for groups and · . or * before water of crystallisation.
Your result Live
Molar Mass
180.156 g/mol
C6H12O6 · 24 atoms per formula unit
- Mass of One Molecule
- 2.992 × 10⁻²² g
- C40.00%
- H6.71%
- O53.28%
Composition
3 rowsHow this is calculated
M = Σ (atoms of each element × its atomic weight) · moles = grams ÷ M · molecules = moles × 6.02214076 × 10²³
- M
- Molar mass in g/mol (numerically equal to the molecular weight in daltons)
Count the atoms of each element in the formula — multiplying everything inside brackets by the number after them, and adding water of crystallisation — then multiply each count by the element's standard atomic weight and add them up. Glucose, C6H12O6, is 6 × 12.011 + 12 × 1.008 + 6 × 15.999 = 180.156 g/mol.
Assumptions & sources
- Standard atomic weights for natural isotopic composition; isotopically labelled compounds differ.
- Charges in ion formulas are ignored (an electron's mass is negligible).
- 1Standard atomic weights (abridged values) — IUPAC Commission on Isotopic Abundances and Atomic Weights (CIAAW)
- 2Avogadro constant (exact): 6.022 140 76 × 10²³ mol⁻¹ — BIPM — The International System of Units (SI), 9th edition
Calculator ID SCI-MOLARMASS-001 · version 1.0.0
Common questions
What is the molar mass of water?
H2O = 2 × 1.008 + 15.999 = 18.015 g/mol.
How do I convert grams to moles?
Divide the mass by the molar mass. 90 g of glucose ÷ 180.16 g/mol = 0.4996 mol.
How do I enter a hydrate?
Put a dot, full stop or asterisk before the water: CuSO4·5H2O, CuSO4.5H2O or CuSO4*5H2O all give 249.68 g/mol.