Molar Mass Calculator
Type a chemical formula and get its molar mass with a full element-by-element breakdown. Add grams or moles to convert, and volume to get molarity.
Molar mass of a compound
Fill grams or moles to convert between them. Add volume to get molarity (mol/L). Capital letters matter: Co is cobalt, CO is carbon monoxide.
How to calculate molar mass
Molar mass is the mass of one mole of a substance, in g/mol. Add the atomic masses of every atom in the formula: Molar mass = Σ (number of atoms × atomic mass).
Worked example: glucose, C6H12O6
Carbon: 6 × 12.011 = 72.066. Hydrogen: 12 × 1.008 = 12.096. Oxygen: 6 × 15.999 = 95.994. Total = 72.066 + 12.096 + 95.994 = 180.156 g/mol.
Formulas with brackets and hydrates
For Ca(OH)2 the 2 outside the bracket multiplies everything inside: 1 Ca, 2 O, 2 H, giving 40.078 + 2 × 15.999 + 2 × 1.008 = 74.092 g/mol. For a hydrate such as CuSO4·5H2O, type it as CuSO4.5H2O and the water is added 5 times: 159.602 + 5 × 18.015 = 249.677 g/mol.
Moles, grams and particles
Moles = mass ÷ molar mass. Number of particles = moles × 6.022 × 1023 (Avogadro's number). Molarity = moles ÷ volume in litres.
About the atomic masses
Calvo uses standard atomic weights rounded to 3 to 5 significant figures, as printed in most textbooks. Your textbook or exam may round differently (for example Cl = 35.5, or Cu = 63.5), so a last-digit difference is normal. Follow the values given in your paper.
FAQ
How do I find the molar mass of a compound?
Add up the atomic masses of all atoms in the formula. For H2O it is 2 x 1.008 + 15.999 = 18.015 g/mol.
What is the molar mass of water?
18.015 g/mol, usually rounded to 18 in school problems.
What is the molar mass of NaCl?
58.44 g/mol (Na 22.990 + Cl 35.45).
How do I handle brackets like Ca(OH)2?
The number after the bracket multiplies every atom inside it. Ca(OH)2 has 1 Ca, 2 O and 2 H.
How do I type a hydrate such as CuSO4·5H2O?
Type CuSO4.5H2O with a full stop. The number before H2O is applied to the water part.
How many particles are in one mole?
6.022 x 10^23, which is Avogadro's number. Calvo shows the particle count when you enter grams or moles.
Why is my textbook answer slightly different?
Books round atomic masses differently, for example Cl = 35.5. Use the values your syllabus gives.
Does it work offline?
Yes. The calculation runs in your browser and the page is cached after your first visit.