Convert one species to another via the mole ratio of a balanced equation: moles B = moles A × (coefB ÷ coefA).
About this tool
The Stoichiometry Calculator is a free, in-browser chemistry tool that converts a known amount of one species (A) into the amount of another species (B) in a balanced chemical reaction, using the mole ratio of their coefficients. Enter the balancing coefficients of A and B, a known amount of A in moles or grams, and the molar masses needed for any gram conversions.
The convention is simple: coefficients are the whole numbers in front of each formula in an already-balanced equation (for 2H₂ + O₂ → 2H₂O, hydrogen's coefficient is 2 and water's is 2). The tool converts grams of A to moles with A's molar mass, applies the ratio moles B = moles A × (coefB / coefA), then converts to grams of B with B's molar mass.
All arithmetic happens locally in your browser with nothing uploaded, so it is dependable for homework, lab prep and limiting-reagent style calculations between any two species.
Frequently asked questions
What convention do the coefficients follow?
They are the stoichiometric coefficients from an already-balanced equation — the whole numbers in front of each formula. For 2H₂ + O₂ → 2H₂O, H₂ has coefficient 2 and H₂O has coefficient 2. You balance the equation first, then enter the two coefficients.
How is the amount of B calculated?
It uses the mole ratio: moles of B = moles of A × (coefficient of B ÷ coefficient of A). If you enter grams, A is first divided by its molar mass to get moles, and B's moles are multiplied by B's molar mass for grams.
When do I need to enter molar masses?
A molar mass for A is required only when the known amount is in grams; the molar mass of B (in g/mol) is optional and used only to also report the mass of B. In pure mole-to-mole work you can ignore both.
Can A and B be any pair of species?
Yes — A and B can each be a reactant or a product. The mole ratio comes only from their coefficients in the balanced equation, so the tool works for reactant-to-product, product-to-reactant, or reactant-to-reactant conversions.
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