Molar Mass Calculator
Any formula incl. hydrates (CuSO4·5H2O) & nested brackets — element-by-element working, % composition & presets.
Common compounds
💡 Brackets nest — K4[Fe(CN)6] works — and hydrates use · (or a dot): CuSO4·5H2O. Capitalisation matters: CO is carbon monoxide, Co is cobalt.
Molar mass of CuSO4·5H2O
249.68 g/mol
Elements
4
Atoms / unit
21
Mass of 1 molecule
4.146e-22 g
🧾 Element-by-element working
| Element | Atoms | Atomic mass | Subtotal | % by mass |
|---|---|---|---|---|
| O · Oxygen | × 9 | 15.999 | 143.991 | 57.67% |
| Cu · Copper | × 1 | 63.546 | 63.546 | 25.45% |
| S · Sulfur | × 1 | 32.06 | 32.060 | 12.84% |
| H · Hydrogen | × 10 | 1.008 | 10.080 | 4.04% |
| Total | 21 | 249.677 | 100% |
🧱 Percent composition
Each element's share of the compound's mass.
💡 Atomic masses are standard IUPAC values. Molar mass in g/mol equals the molecular mass in u — the same number serves both.
⚗️Any formula, fully worked
Type any chemical formula — simple (H2O), bracketed (Ca(OH)2), nested (K4[Fe(CN)6]), or a hydrate (CuSO4·5H2O) — and get the molar mass with the element-by-element workinglaid out like your notebook: every element's count, atomic mass, subtotal, and percent compositionwith a colour-banded bar. Plus the mass of a single molecule via Avogadro's number, and one-click presets for the compounds every exam loves.
📊Everything you'd want to know
- Full bracket support, including nested [ ] and ( ), and · hydrate notation.
- The working table: atoms × atomic mass = subtotal for each element, summing to the total.
- Percent composition — the follow-up question examiners always ask — computed and drawn.
- Mass of one molecule (M ÷ Nₐ) and total atom count per formula unit.
- Nine common-compound presets from water to potassium ferrocyanide.
🧮The maths
Brackets multiply everything inside: Ca(OH)2 has one Ca, two O, two H. Hydrate dots add whole water units: CuSO4·5H2O carries five complete H2O molecules — 10 extra H and 5 extra O.
💡Formula-writing gotchas
- Capitalisation is chemistry: CO = carbon monoxide, Co = cobalt, and 'HE' is an error while 'He' is helium.
- Numbers after a bracket multiply the whole bracket; numbers after an element multiply only that element.
- Molar mass (g/mol) and molecular mass (u) share the same numeric value — one mole was defined to make that true.
- For % composition questions, this page's table IS the full working — copy it.
💡 Frequently Asked Questions
How do I calculate molar mass?+
Multiply each element's atom count by its atomic mass and add them up. For H2O: 2×1.008 + 16.00 = 18.02 g/mol. This calculator parses any formula — brackets, nesting, hydrates — and shows that working element by element.
What is the molar mass of CuSO4·5H2O?+
249.69 g/mol — copper 63.55, sulphur 32.07, four oxygens 64.00, plus five water molecules adding 90.08. The · means five whole H2O units ride along with each CuSO4.
How do I find percent composition?+
Divide each element's mass contribution by the total molar mass and multiply by 100. In water, oxygen is 16.00 ÷ 18.02 = 88.8%. The calculator computes this for every element automatically, with a visual bar.
How do brackets work in chemical formulas?+
A number after a bracket multiplies everything inside: Ca(OH)2 means one calcium plus two OH groups — two oxygens and two hydrogens. Nesting works the same way outward: K4[Fe(CN)6] has 6 carbons and 6 nitrogens inside the ferrocyanide bracket.
Is molar mass the same as molecular weight?+
Numerically yes: molecular mass in atomic mass units (u) equals molar mass in g/mol — the mole is defined to make them match. Use g/mol when working with laboratory-scale amounts.