Molar Mass Calculator
Type a chemical formula. Get its molar mass, the mass contributed by each element, percent composition, and grams ↔ moles in one place.
Case matters: Co is cobalt, CO is carbon monoxide. Brackets, [complexes] and hydrates (·5H2O) are supported.
M
Molar mass of C₆H₁₂O₆
g/mol
24 atoms per formula unit
1 u
Mass of one formula unit
g
| Element | Atoms | Atomic mass | Subtotal (g/mol) | 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 |
M = 6 × 12.011 + 12 × 1.008 + 6 × 15.999 = 180.156 g/mol
Grams ↔ moles for C₆H₁₂O₆
g
n
Moles
mol
n = 10 g ÷ 180.156 g/mol
N
Formula units (molecules)
N = n × 6.022 × 10²³ mol⁻¹
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How to calculate molar mass by hand
- Write the formula and count atoms of each element. Expand brackets: in Al₂(SO₄)₃ there are 3 × 1 = 3 S and 3 × 4 = 12 O.
- Look up each element’s atomic weight on the periodic table (Al 26.982, S 32.06, O 15.999).
- Multiply and add: 2(26.982) + 3(32.06) + 12(15.999) = 342.14 g/mol.
The molar mass is the bridge between the mass you can weigh on a balance and the number of particles a balanced equation talks about. Every stoichiometry problem crosses it twice: grams to moles on the way in, moles to grams on the way out.
Molar masses of common compounds
| Compound | Formula | Molar mass (g/mol) |
|---|---|---|
| Water | 18.02 | |
| Sodium chloride | 58.44 | |
| Carbon dioxide | 44.01 | |
| Sulfuric acid | 98.07 | |
| Glucose | 180.16 | |
| Ammonia | 17.03 | |
| Calcium carbonate | 100.09 | |
| Sodium hydroxide | 40.00 | |
| Hydrochloric acid | 36.46 | |
| Ethanol | 46.07 | |
| Oxygen gas | 32.00 | |
| Nitric acid | 63.01 | |
| Sucrose | 342.30 | |
| Methane | 16.04 | |
| Caffeine | 194.19 |
Frequently asked questions
How do you calculate molar mass?
Multiply each element’s standard atomic weight by the number of atoms of that element in the formula, then add the results. For water, H₂O: 2 × 1.008 + 1 × 15.999 = 18.015 g/mol.
How do brackets and hydrates work in the formula box?
A subscript after a bracket multiplies everything inside it, so Ca(OH)₂ has 1 Ca, 2 O and 2 H. For hydrates use a dot, asterisk or middle dot:
CuSO4·5H2O or CuSO4*5H2O adds five waters. Square brackets for complexes, like K4[Fe(CN)6], work the same way.What is the difference between molar mass, molecular weight and formula mass?
Numerically they are the same. Molar mass has units of g/mol and applies to a mole of substance. Molecular weight (or relative molecular mass) is the same number without units, for one molecule relative to 1/12 of carbon-12. “Formula mass” is used for ionic compounds such as NaCl that do not form discrete molecules.
Which atomic masses does this calculator use?
IUPAC abridged standard atomic weights (e.g. C = 12.011, O = 15.999, Cl = 35.45). For radioactive elements without a standard weight the mass of the longest-lived isotope is used. Your textbook may round (e.g. Cl = 35.5); differences in the second decimal place come from that.
How do I convert grams to moles?
Divide the mass in grams by the molar mass: n = m ÷ M. 10.0 g of glucose (180.16 g/mol) is 0.0555 mol. To go from moles to grams, multiply: m = n × M.
How do I find percent composition?
Divide each element’s total mass in the formula by the molar mass and multiply by 100. The table under the result does this for every element; the percentages add to 100 %.