Molar mass calculator
Type a chemical formula, for example H2SO4, Ca(OH)2 or CuSO4·5H2O. The calculator shows the molar mass and what each element adds to it. Atomic weights are from IUPAC (CIAAW), as in the table.
Breakdown by element
M(Ca(OH)2) = 40.078 + 2 × 15.999 + 2 × 1.0080 = 74.092 g/mol
The result is rounded to the precision of the least precise atomic weight. Atomic weights from IUPAC (CIAAW).
Molar mass problems with Ca(OH)₂
For school problems (Ca = 40, O = 16, H = 1): M(Ca(OH)₂) = 74 g/mol
Problem 1
How many moles are in 296 g of Ca(OH)₂?
n = m ÷ M = 296 g ÷ 74 g/mol
Answer: 4 mol
Problem 2
What is the mass of 0.5 mol of Ca(OH)₂?
m = n × M = 0.5 mol × 74 g/mol
Answer: 37 g
Problem 3
What is the mass percentage of Ca in Ca(OH)₂?
w(Ca) = M(Ca) ÷ M(Ca(OH)₂) = 40 ÷ 74 ≈ 0.541
Answer: 54.1%
Common substances
What is molar mass?
Molar mass M is the mass of one mole of a substance, about 6.022 × 10²³ of its particles. It is measured in grams per mole (g/mol).
To find it, add up the atomic weights of all the atoms in the formula: multiply each element’s atomic weight by its subscript, the number of its atoms. In g/mol, the molar mass equals the relative molecular mass Mr.
For water: M(H₂O) = 2 × 1.0080 + 15.999 = 18.015 g/mol.