How this calculator works
Weigh the sample and divide its mass in grams by molar mass in g/mol. Select a listed substance, parse another formula, or enter a measured molar mass. Formula mode uses IUPAC 2021 conventional weights and accepts groups and hydrates. Purity and hydration must match the actual sample.
Formula
n = m(g)/M(g/mol); N = n x N_A; N_A = 6.02214076 x 10^23 mol^-1, exactly.
Worked example
18.015 g H2O is 1 mol. With M = 100 g/mol, 25 g is 0.25 mol.
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Frequently asked questions
Can I enter zero mass?
Zero mass gives zero moles when molar mass is known. Inferring molar mass requires positive mass and amount.
Does the calculation account for purity?
Use the mass of the substance of interest. Correct the weighed mass for purity separately.
Which atomic weights are appropriate?
Natural-isotope conventional atomic weights suit ordinary samples; enriched materials require isotope-specific molar mass.