Molar Mass Calculator
Calculate molar mass from a chemical formula, expand groups and hydrates, and convert a sample mass in grams to moles using CIAAW atomic weights.
Find the mass of one mole of a substance from its chemical formula, then convert an entered sample mass in grams to moles. The element table shows exactly how every subscript contributes, which helps catch a missing parenthesis or an incorrect hydration number.
How to use this tool
- Enter a formula such as H2O, Ca(OH)2 or CuSO4·5H2O.
- Enter the sample mass in grams; use zero if you only need molar mass.
- Check the expanded atom counts and each element’s contribution.
- Read the molar mass in g/mol and the amount in moles.
Formula
M ≈ Σ(nᵢ × Aᵢ) g/mol; amount = sample mass / M
nᵢ is the number of atoms of element i. Aᵢ is its nominal CIAAW 2024 abridged standard atomic weight. The numerical conversion to g/mol is appropriate at this table’s precision; it is not an isotope-specific exact mass.
Example
For Ca(OH)2, count one Ca, two O and two H atoms. The sum is 40.078 + 2 × 15.999 + 2 × 1.008 = 74.092 g/mol. A 37.046 g sample therefore contains 0.5 mol.
Frequently asked questions
How do I enter a hydrate?
Separate components with the middle dot ·. CuSO4·5H2O adds five waters, giving ten H and nine O atoms overall. An ordinary decimal point is rejected to avoid confusing hydrates with fractional subscripts.
Can I use ions, isotope labels or polymers?
This parser accepts neutral formula notation with positive integer subscripts and nested round or square brackets. It rejects explicit charges, isotope labels, variable subscripts and elements without standard atomic weights. It checks notation, not whether a substance exists.
Why does another reference give a different value?
Atomic-weight rounding and natural isotope variation can change the last digits. Enriched isotopes need different data. The displayed precision does not represent an uncertainty estimate.
Are formulas sent to a chemistry service?
No. The calculation uses an embedded reference table in your browser. Formulas are limited to 500 characters, twelve nested groups and one million expanded atoms.
Sources
Last updated: 2026-10-30