Molar Mass Calculator
Molar mass calculator — type a chemical formula like H2SO4 or Ca(OH)2 and get the molar mass (g/mol) plus each element's mass percentage. Curriculum-aligned.
Molar Mass Calculator
Type a chemical formula — use brackets for groups, e.g. Ca(OH)2, and a middle dot for hydrates, e.g. CuSO4·5H2O.
- Curriculum
- English (global) — Cambridge International + IB
- Built against
- Cambridge IGCSE Chemistry 0620 + IB Diploma (2023–2025) — Relative Formula Mass
- Unit system
- SI primary; US/imperial readout below
- First published
- 1 Jun 2026
- Last updated
- 4 Sep 2026
View authoritative scientific sources
- IUPAC — standard atomic weights (CIAAW 2021)
- BIPM SI Brochure, 9th edition (2019)
- NIST — Avogadro constant
- Molar mass — Encyclopædia Britannica
⚠️ Educational use only — see full disclaimer
EDUCATIONAL USE DISCLAIMER
This calculator is provided for educational and reference purposes only. It is not a substitute for instruction from a qualified teacher, your prescribed textbook, or your school's official curriculum materials.
When preparing for examinations, always cross-check our calculations and notation against your current syllabus and your teacher's guidance. Syllabus conventions and accepted notation vary between curricula and may change between examination years.
If you believe any calculation, notation, or curriculum reference in this tool is inaccurate, please let us know via the feedback button. We review feedback promptly and update tools when verified corrections are needed.
RECATOOLS accepts no liability for academic, examination, professional, or research outcomes arising from use of this tool.
How to Use the Molar Mass Calculator
Pick your curriculum
Use the curriculum pills above to match your syllabus (Cambridge, SEAB, SPM, SBMPTN, 高考, 學測 or HKDSE). Terminology, the worked example and the whole page follow your selection.
Type a formula
Enter a chemical formula using ordinary element symbols, e.g. H2SO4. Use brackets for groups, Ca(OH)2, and a middle dot for hydrates, CuSO4·5H2O.
Read the molar mass
The calculator sums the atomic masses (IUPAC standard atomic weights) and shows the molar mass in g/mol plus each element's mass percentage.
Check against your syllabus
The Tool Information block shows exactly which syllabus this is built against. Spot something off? Use the feedback button — we review every report.
Molar Mass, in Your Curriculum's Words
Molar Mass (sum of atomic masses × subscripts)
Example: Find the molar mass of sulfuric acid, H₂SO₄.
Sum the atomic masses: 2 × 1.008 (H) + 1 × 32.06 (S) + 4 × 15.999 (O)
M = 2.016 + 32.06 + 63.996 = 98.07 g/mol
Molar mass is the mass of one mole of a substance, in grams per mole (g/mol). For a compound it is the sum of the atomic masses of each element times the number of atoms of that element in the formula. This calculator parses the formula you type — including nested brackets and hydrates such as CuSO4·5H2O — then sums the IUPAC standard atomic weights of each element.
Molar mass in g/mol is numerically equal to the relative formula mass (Mr), which is unitless. We also show each element's mass percentage, which is useful for percentage-composition questions. All calculation happens in your browser — nothing is uploaded.
Molar mass is the bridge between the macroscopic world of grams on a balance and the microscopic world of atoms and molecules.
10 Facts About Molar Mass
Molar mass is the mass of one mole of a substance, in g/mol.
It is numerically equal to the relative formula mass (Mr), which is unitless.
Sum atomic mass × subscript across the whole formula.
Atomic masses are weighted averages over natural isotopes.
Water (H₂O) is 18.015 g/mol.
A subscript applies to the element/group before it; brackets group.
Hydrates (·nH₂O) add n water molecules to the mass.
Standard atomic weights are set by IUPAC (CIAAW).
The atomic-mass scale is anchored to carbon-12 = exactly 12.
This calculator runs in your browser — your working stays private.
Frequently Asked Questions
- The calculator parses your formula, counts how many atoms of each element are present (including inside bracketed groups and hydrates), then sums the IUPAC standard atomic weights. For example H₂SO₄ is 2 × 1.008 + 32.06 + 4 × 15.999 = 98.07 g/mol.
- The value is the same; only the units differ. Relative formula mass (Mr) is unitless because it is a ratio against 1/12 the mass of carbon-12, whereas molar mass carries the unit g/mol. For H₂O both are 18.015.
- Use brackets for repeated groups, e.g. Ca(OH)2 means one calcium with two OH groups. For hydrates use a middle dot, e.g. CuSO4·5H2O, and the calculator adds five water molecules. Nested brackets are also supported.
- Yes, it matters a lot. Element symbols start with a capital letter followed by a lowercase letter if any — Co is cobalt but CO is carbon and oxygen. Type symbols exactly as on the periodic table.
- The chemistry is identical worldwide because element symbols and atomic weights are international standards. What changes is the terminology; for example "molar mass" is written 摩尔质量 in mainland China, 莫耳質量 in Taiwan and 摩爾質量 in Hong Kong.
- IUPAC (CIAAW) standard atomic weights, which are weighted averages over natural isotopes. For radioactive elements without a standard atomic weight, we use the mass number of the most stable isotope.
- Yes. The results table shows each element's mass percentage, calculated as that element's contributed mass divided by the total molar mass.
- The Tool Information block lists the exact syllabus for your selected curriculum (e.g. SEAB O-Level Chemistry 6092 or SPM Kimia 4541). It is a study aid, not a substitute for your official syllabus or teacher.
- Completely free, no account or usage limit. It runs entirely in your browser and collects no data.
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Method & sources
How it computes
M = sum of the standard atomic weights of the constituent atoms. A post-2019 subtlety most tables ignore: the molar mass constant is no longer exactly 1 g/mol. Fixing the Avogadro constant broke its exact tie to carbon-12, so M_u = 0.99999999965(30) x 10^-3 kg/mol — a difference far below bench precision, but the exactness is gone.
What this tool implements
- Atomic weights follow CIAAW 2021. For the 14 elements published as intervals the conventional value is used and labelled as such, because an interval cannot be summed.
- The molar mass constant is treated as measured rather than exactly 1 g/mol, following the 2019 SI redefinition.
- Isotopically enriched or depleted material is outside standard atomic weights entirely — heavy water is the obvious case, and a standard table will be wrong for it.
Sources
- IUPAC Commission on Isotopic Abundances and Atomic Weights, Standard Atomic Weights: https://www.ciaaw.org/atomic-weights.htm
- Prohaska T, Irrgeher J, Benefield J, et al. Standard atomic weights of the elements 2021 (IUPAC Technical Report). Pure Appl Chem 2022;94(5):573-600: https://doi.org/10.1515/pac-2019-0603
- CODATA molar mass constant, NIST: https://physics.nist.gov/cgi-bin/cuu/Value?mu
What can make this go out of date
- None at runtime. CIAAW revises every two years; the set in use is 2021 and is stated.
Pick up where you left off
Stored only in this browser — never sent to our servers.