⚗️ Molar Mass Calculator
Type a chemical formula to get its molar mass in g/mol, the percent composition by element, and grams ↔ moles — with parentheses and hydrates.
Case matters: Co is cobalt, CO is carbon monoxide. Use ( ) or [ ] for groups and · or . for hydrates.
| Element | Atoms | Atomic weight | Mass (g/mol) | % by mass |
|---|---|---|---|---|
| C Carbon | 6 | 12.011 | 72.066 | 40.00% |
| H Hydrogen | 12 | 1.008 | 12.096 | 6.71% |
| O Oxygen | 6 | 15.999 | 95.994 | 53.28% |
Grams ↔ moles
= 0.055507 mol = 3.3427e+22 formula units
= 90.0780 g
What Molar Mass Calculator Does
This molar mass calculator reads a chemical formula as you type it — including parentheses, square brackets and hydrates such as CuSO4·5H2O — and returns the molar mass in grams per mole, a breakdown by element with percent composition, and a converter between grams, moles and number of formula units.
Atomic weights are the IUPAC standard values shown to three decimal places (H 1.008, C 12.011, O 15.999), the same precision used in most textbooks and answer keys. Elements with no stable isotopes, such as technetium or radon, have no standard atomic weight; for those the mass number of the longest-lived isotope is used and shown in brackets.
How to Use Molar Mass Calculator
- Type a chemical formula, or tap an example
- Read the molar mass in g/mol and the Hill-order formula
- Check each element’s contribution and percent by mass
- Convert between grams and moles below the result
Formula Used by Molar Mass Calculator
Molar mass
M = Σ (atoms of each element × its atomic weight)
Worked example
Glucose, C6H12O6.
- C: 6 × 12.011 = 72.066
- H: 12 × 1.008 = 12.096
- O: 6 × 15.999 = 95.994
- 72.066 + 12.096 + 95.994
Result: 180.156 g/mol — 40.00% C, 6.71% H, 53.28% O by mass.
Grams, moles and particles
moles = grams ÷ M · particles = moles × Nₐ
- Nₐ
- Avogadro constant, exactly 6.02214076 × 10²³ per mole
Worked example
10 g of glucose.
- 10 ÷ 180.156 = 0.05551 mol
- 0.05551 × 6.02214076 × 10²³
Result: 0.0555 mol, or about 3.343 × 10²² molecules.
Molar Masses of Common Compounds
| Compound | Formula | Molar mass (g/mol) |
|---|---|---|
| Water | H₂O | 18.015 |
| Ammonia | NH₃ | 17.031 |
| Carbon dioxide | CO₂ | 44.009 |
| Ethanol | C₂H₅OH | 46.069 |
| Sodium chloride | NaCl | 58.440 |
| Calcium hydroxide | Ca(OH)₂ | 74.092 |
| Sodium bicarbonate | NaHCO₃ | 84.006 |
| Sulfuric acid | H₂SO₄ | 98.072 |
| Calcium carbonate | CaCO₃ | 100.086 |
| Glucose | C₆H₁₂O₆ | 180.156 |
| Caffeine | C₈H₁₀N₄O₂ | 194.194 |
| Copper(II) sulfate pentahydrate | CuSO₄·5H₂O | 249.677 |
Source: CIAAW — Standard Atomic Weights
How to Read Your Result
Why your textbook may differ slightly
Some books round atomic weights to two decimals or fewer (H 1.01, O 16.00), which moves the answer in the second decimal place. Water comes out as 18.02 instead of 18.015. Use the precision your course asks for; the element table shows the weights used so you can match them.
Hydrates
The water in a hydrate is part of the solid’s mass, so it counts. Anhydrous copper sulfate, CuSO₄, is 159.604 g/mol; the blue pentahydrate is 249.677 g/mol, about 36% water by mass.
Limitations & Accuracy Notes
- Ionic charges written at the end of a formula (SO4^2-) are ignored; the mass of the electrons is negligible for this purpose.
- Isotope-specific formulas (such as D₂O written with D) are not supported; use the element symbol H and correct separately if needed.
- Standard atomic weights apply to normal terrestrial materials; isotopically enriched samples differ.
Frequently Asked Questions
How do you calculate molar mass?
What is the difference between molar mass and molecular weight?
How do I enter parentheses and hydrates?
How do I convert grams to moles?
What is percent composition?
Why does capitalization matter?
Which atomic weights are used?
References & Further Reading
- CIAAW — Standard Atomic Weights — IUPAC Commission on Isotopic Abundances and Atomic Weights
- CIAAW — Abridged Standard Atomic Weights
- NIST CODATA — Avogadro constant — Exact since the 2019 SI redefinition