Stoichiometry Calculator

Grams to moles to moles to grams, through the mole ratio.

Written and maintained by Mohit PatelLast checked August 4, 2026How we build these

Mass of the known substance

Its molar mass

g/mol

Its coefficient in the equation

From the BALANCED equation. Unbalanced coefficients give a wrong ratio.

Coefficient of what you want

Molar mass of what you want

g/mol

Mass of the target substance

36.03 g

2 mol → 2 mol, through 2 : 2

Mass produced36.03 g

Moles of the known substance2

Mole ratio2 : 2

Moles of the target2

Every stoichiometry problem is this one path: grams to moles by dividing by molar mass, moles to moles through the balanced coefficients, then moles back to grams. Nothing else is happening, however many steps a question wraps around it. The coefficients must come from a balanced equation. Using the unbalanced ones is the single commonest error, and it produces an answer that is wrong by a clean factor — often a whole number, which makes it look deliberate. This assumes complete reaction with the known substance limiting. If both reactant amounts are given, work out the limiting reagent first, because the excess one cannot be used as the starting point.

How the Stoichiometry Calculator works

Enter the mass of what you have, the two coefficients from the balanced equation, and the molar masses, and this returns the mass of what you get. Every stoichiometry problem reduces to this one path however many steps a question wraps around it.

Also known as: mole ratio calculator · mass to mass stoichiometry calculator · gram to gram conversion chemistry · how to do stoichiometry

Where to go next

The Stoichiometry question rarely arrives on its own. These are the ones that usually come with it:

Limiting Reagent Calculator — Fewest equivalents, not fewest moles.
Percent Yield Calculator — Actual over theoretical, and what a figure above 100 means.
Chemical Equation Balancer — Any equation, including the redox ones that take a page by hand.
Theoretical Yield Calculator — A yield over 100% means wet product, not a good day.

Sources

Frequently asked questions

How do I do a stoichiometry calculation?

Convert grams to moles by dividing by molar mass, convert moles to moles using the coefficients from the balanced equation, then convert back to grams by multiplying by the target's molar mass.

Where do the coefficients come from?

The balanced equation, and only the balanced equation. Using unbalanced coefficients is the commonest error here, and it gives an answer wrong by a clean factor that looks deliberate rather than mistaken.

What if I am given both reactant amounts?

Then find the limiting reagent first. Only the limiting reagent can be used as the starting point — the one in excess is left over and calculating from it overstates the yield.

Does this account for percent yield?

No, this gives the theoretical yield assuming complete reaction. Multiply by your percent yield to get the actual expected mass.

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