What is stoichiometry?

The arithmetic of balanced chemical equations: how much of one substance reacts with or produces how much of another, based on their mole ratio.

Why do coefficients matter?

Because the equation must conserve atoms. In 2H₂ + O₂ → 2H₂O, 2 mol H₂ react with 1 mol O₂ to make 2 mol H₂O — the 2:1:2 ratio is what stoichiometry rides on.

How do I get molar masses?

Add up atomic weights from a periodic table, or paste a formula into our atomic mass calculator. For glucose (C₆H₁₂O₆) it is 180.16 g/mol; for CO₂ it is 44.01 g/mol.

Can I use moles directly, without molar mass?

Yes — switch the "Input as" or "Output as" toggle to moles and the corresponding molar mass field disappears.

What about limiting reagents?

Run the calculator twice, once for each reactant, and compare moles of product. The smaller product yield identifies the limiting reagent.

Is the stoichiometry calculator free?

Yes — free, no signup, runs entirely in your browser.

Stoichiometry Calculator

Convert mass or moles between reactants and products using the mole ratio.

Written by Golam Rabbani, Founder & Lead Engineer

This interactive tool requires JavaScript. Read the formula and worked example below; you can compute the result by hand.

How to use this stoichiometry calculator

Label the reactant (A) and product (B).
Enter the balanced-equation coefficients a (for A) and b (for B).
Choose whether you are entering A in grams or moles, and whether you want B in grams or moles.
Enter the amount of A and the molar masses you need. Press Calculate.
Use Copy to grab the result or Reset to start a new reaction.

About this stoichiometry calculator

A balanced chemical equation gives you a mole ratio between reactants and products. For a generic reaction a · A → b · B, every a moles of A produces b moles of B — and that ratio is exact regardless of the absolute amounts. The stoichiometry calculator converts mass to moles, applies the b ⁄ a ratio, and (optionally) converts product moles back to grams using the product molar mass. It handles the most common homework variant of stoichiometry: "I have x grams of A; how many grams of B does it produce?"

Worked example: combustion of glucose, C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O. How much CO₂ comes from burning 18.0 g of glucose? Set a = 1 (glucose coefficient), b = 6 (CO₂ coefficient), molar mass of glucose = 180.16 g/mol, molar mass of CO₂ = 44.01 g/mol. Moles of glucose = 18.0 ⁄ 180.16 = 0.0999 mol. Moles of CO₂ = 0.0999 × (6 ⁄ 1) = 0.5994 mol. Mass of CO₂ = 0.5994 × 44.01 = 26.4 g. Same equation works in reverse — the tool will tell you what mass of glucose is needed to produce a target mass of CO₂, just by flipping which side you call "input".

FAQ

What is stoichiometry?: The arithmetic of balanced chemical equations: how much of one substance reacts with or produces how much of another, based on their mole ratio.
Why do coefficients matter?: Because the equation must conserve atoms. In 2H₂ + O₂ → 2H₂O, 2 mol H₂ react with 1 mol O₂ to make 2 mol H₂O — the 2:1:2 ratio is what stoichiometry rides on.
How do I get molar masses?: Add up atomic weights from a periodic table, or paste a formula into our atomic mass calculator. For glucose (C₆H₁₂O₆) it is 180.16 g/mol; for CO₂ it is 44.01 g/mol.
Can I use moles directly, without molar mass?: Yes — switch the "Input as" or "Output as" toggle to moles and the corresponding molar mass field disappears.
What about limiting reagents?: Run the calculator twice, once for each reactant, and compare moles of product. The smaller product yield identifies the limiting reagent.
Is the stoichiometry calculator free?: Yes — free, no signup, runs entirely in your browser.