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Chemistry Tools · Updated October 21, 2026 · Reviewed by FormatFlow Editorial

Stoichiometry Calculator

You can scale a balanced chemical equation from one known amount: enter the equation, choose a species, give its mass or moles, and get the moles and mass of every species.

Runs in your browserFree · No sign-up · No watermark
AMOUNT → ALL SPECIESRuns in your browser
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Everything runs locally in this tab. No file is uploaded while the tool loads.

This tool runs in your tab. Nothing is uploaded and no copy is stored.

How files are handled

At a glance

Works with
AMOUNT → ALL SPECIES
Processing
In your browser
Price
Free, no account
Updated
October 21, 2026
All Chemistry Tools

About Stoichiometry Calculator

Stoichiometry turns a balanced equation into quantities you can measure. The coefficients give a mole ratio, so once one species is known — in grams or moles — the amount of every other reactant and product follows by simple proportion.

This calculator balances the equation first, then uses the known amount to scale every species. You get molar masses, moles and masses in one table, a mass check for both sides, and the working written out so each conversion can be followed step by step.

What this tool does

The details that matter when you use Stoichiometry Calculator for real work.

  • Balances the equation for you

    Type the equation as written and the shared solver finds the smallest whole-number coefficients before any amounts are calculated.

  • Mass or moles input

    Give the known species as a mass with its molar mass, or directly in moles; the tool handles the conversion to moles internally.

  • Every species computed

    The results table lists the coefficient, molar mass, moles and mass of every reactant and product, with the known species highlighted.

  • Molar masses from formulas

    Each species' molar mass comes from the same formula parser as the molar mass calculator, including grouped formulas and hydrates.

  • Mass check

    A summary compares total reactant mass with total product mass, which should match when the equation is balanced.

  • Step-by-step working

    The working panel shows the balanced equation, the conversion to moles of the known species and the coefficient ratio for each result.

How to use Stoichiometry Calculator

No account, no installation — the whole job happens in this browser tab.
  1. 01

    Enter the equation

    Type the reaction with ->, → or = between the sides and + between formulas; the balancer fixes the coefficients.

  2. 02

    Choose the known species

    Pick the reactant or product whose amount you know from the dropdown; the molar mass hint updates from its formula.

  3. 03

    Enter the known amount

    Give a mass in grams with the molar mass, or switch to moles and enter the amount directly.

  4. 04

    Read the results table

    Every species gets its coefficient, molar mass, moles and mass; the highlighted row is the one you entered.

  5. 05

    Check the working

    Follow the coefficient ratios and mass check in the step panel, and remember the result assumes ideal conversion.

How this tool works

Works with
AMOUNT → ALL SPECIES
Processing
Client-side, in your browser. Nothing is uploaded.
Requirements
Chrome, Edge, Firefox or Safari · JavaScript enabled

Limitations worth knowing

  • Ideal stoichiometry only: it assumes complete conversion along the balanced ratio and does not identify a limiting reagent or excess reactant.
  • No percent yield, equilibrium, side reactions or gas-law corrections are included; the output is theoretical moles and mass.
  • Molar masses use conventional standard atomic weights, so results for unstable or isotopically modified species are approximate.

Privacy and file handling

Equations and amounts are processed in your browser tab. Nothing you enter is uploaded, stored or logged, and the calculator makes no network request.

Read the full privacy policy

Stoichiometry Calculator FAQ

Short, direct answers to the questions people ask before using this tool.
What is stoichiometry?
Stoichiometry is the relationship between the amounts of substances in a chemical reaction. The balanced coefficients give the mole ratio, which converts a known amount of one species into the amount of every other species.
Why does the calculator balance the equation first?
Mole ratios only work with the smallest whole-number coefficients. The calculator runs the equation through the same integer solver as the equation balancer, so an unbalanced input such as H2 + O2 -> H2O is corrected to 2H2 + O2 -> 2H2O before scaling.
How do I find the limiting reagent?
This calculator does not determine it. To find it by hand, convert every reactant's available amount to moles, divide each by its coefficient and compare: the smallest quotient is the limiting reagent, and all other reactants are in excess relative to it.
Should I enter the known amount in grams or moles?
Either works. In mass mode the tool divides grams by the molar mass to get moles; the molar mass can be typed or filled from the known species' formula. In moles mode the amount is used directly, which suits solutions and gas problems.
Why do the total masses of reactants and products match?
A balanced equation conserves atoms, and multiplying atom counts by standard atomic masses means the total mass on each side must be equal. The summary shows both totals so the check is visible, with small differences possible from rounding.
Can I calculate a percent yield with this tool?
No. The results are theoretical amounts based on complete conversion along the balanced ratio. Percent yield needs the actual mass obtained from an experiment, which you compare with the theoretical mass by dividing the actual by the theoretical and multiplying by 100.
Does it handle hydrated and grouped formulas in the equation?
Yes. Species such as CuSO4·5H2O and Ca(OH)2 are parsed by the shared formula parser, so their molar masses include the water of crystallization and the atoms inside the brackets.

Background reading

Format guides that explain the trade-offs behind Stoichiometry Calculator.