Chemical Molar Mass Calculator
Pick from 15 common compounds to get molar mass in g/mol, plus the moles and molecule count in any sample mass.
Water, glucose, sulfuric acid and more.
Molar mass is the mass of one mole of a substance, expressed in grams per mole (g/mol). It is a fundamental quantity in chemistry, used for converting between mass and moles and for preparing solutions of precise concentration.
What is a Mole?
A mole is a specific number of particles: exactly 6.022 × 10²³ (Avogadro’s number). For any pure element, the molar mass in g/mol equals the atomic mass shown on the periodic table.
Calculating Compound Molar Mass
To find the molar mass of a compound, sum the atomic masses of all atoms in the formula:
M = Σ (atomic mass × number of atoms)
Example: Water (H₂O)
- 2 × H = 2 × 1.008 = 2.016 g/mol
- 1 × O = 1 × 15.999 = 15.999 g/mol
- Total: 18.015 g/mol
Example: Sodium Chloride (NaCl)
- 1 × Na = 22.990 g/mol
- 1 × Cl = 35.453 g/mol
- Total: 58.443 g/mol
Reference Atomic Masses
Every figure this calculator reports is summed from this one table rather than stored as a finished number, so the arithmetic shown in the result panel always reconciles.
| Element | Symbol | Atomic Mass (g/mol) |
|---|---|---|
| Hydrogen | H | 1.008 |
| Carbon | C | 12.011 |
| Nitrogen | N | 14.007 |
| Oxygen | O | 15.999 |
| Sodium | Na | 22.990 |
| Magnesium | Mg | 24.305 |
| Aluminum | Al | 26.982 |
| Sulfur | S | 32.065 |
| Chlorine | Cl | 35.453 |
| Potassium | K | 39.098 |
| Calcium | Ca | 40.078 |
| Manganese | Mn | 54.938 |
| Iron | Fe | 55.845 |
| Copper | Cu | 63.546 |
These are the IUPAC standard atomic weights carried to three decimals. IUPAC also publishes an abridged table that rounds sulfur to 32.06 and chlorine to 35.45, and a textbook using the abridged values will land about 0.005 g/mol away on sulfuric acid. Neither is wrong. Match whichever table your course or lab uses and stay with it, because mixing the two is what produces answers that miss by a hair and cannot be traced.
Why Molar Mass Matters
Chemists use molar mass constantly for:
- Preparing solutions of known concentration (molarity = moles / volume)
- Stoichiometry, converting between masses in chemical reactions
- Calculating empirical and molecular formulas
- Understanding reaction yields
The weighing bench version
Say a protocol calls for 250 mL of 0.1 M sodium hydroxide. NaOH is 39.997 g/mol, so you need 0.025 mol, which is 1.00 g. Weigh it, dissolve, make up to the mark.
There is a catch worth knowing before you trust that number: solid NaOH pellets pull water out of the air fast enough to gain measurable weight while sitting on the balance pan, and they absorb carbon dioxide as well. Nobody prepares an accurate NaOH standard by weighing. You make it roughly and then titrate it against a primary standard. Molar mass tells you what to aim for, not what you end up with.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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