Atomic Mass of Calcium

M(\mathrm{Ca}) = 0.040078\ \text{kg/mol}

Value	40.0779999579 Da (0.040078 kg/mol) Use in the calculator →
Status	Measured: ± 0.004 Da (1 × 10⁻⁴ relative), standard uncertainty
Source	IUPAC
Categories	Chemistry Water Treatment

Atomic Mass of Calcium in every molar mass unit

Unit	Value
dalton (as molar mass)	40.078 Da
gram per mole	40.078 g/mol
kilogram per mole	0.040078 kg/mol
kilogram per kilomole	40.078 kg/kmol
milligram per millimole	40.078 mg/mmol
pound per pound-mole	40.078 lb/lb-mol
kilodalton (as molar mass)	0.040078 kDa

Learning zone

Calcium at 40.078 g/mol and a charge of 2+ has an equivalent weight of 20.04 g/eq, which is what makes the hardness conversion work: multiply mg/L of Ca²⁺ by 100.09/40.08 = 2.497 and you have mg/L as CaCO₃. A water with 60 mg/L of calcium therefore contributes 150 mg/L of hardness, and hardness is simply the sum of calcium and magnesium expressed on that common scale.

It is the fifth most abundant element in the crust and the most abundant metal in the human body, essentially all of it locked in bone as hydroxyapatite. In a heating system it is the villain: calcium carbonate's inverse solubility means it comes out of solution on the hottest surface available, and a millimetre of scale on a boiler tube can cost several percent of fuel efficiency. Humphry Davy isolated the metal in 1808, again by electrolysis.

Used by 2 solvers

Moles from Mass (n = m/M)

n = \frac{m}{M}

Total Hardness as CaCO₃

\mathrm{TH} = 2.497\,\mathrm{Ca} + 4.118\,\mathrm{Mg}

Revised 16 October 2026

Cite this page

formula.expert. (2026, October 16). Atomic Mass of Calcium. https://formula.expert/constants/atomic-mass-calcium