Balanced reaction amount conversion

Stoichiometry Calculator

Use one known substance in a balanced chemical equation to calculate the amount or mass of another substance. The calculator shows the unit conversion, mole ratio, and unrounded intermediate values.

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Stoichiometry Calculator

Calculator

Enter a balanced equation, select the known and target species, then supply an amount, mass, or molarity with volume.

Inputs
Use an already balanced equation. Known and target selections use stable reaction-side IDs, so repeated formulas remain distinct.

Balanced across N, H.

Supported arrows: ->, →, <=>, and ⇌. State labels are optional.

Load an example

Result
The displayed answer is rounded to eight significant digits; calculations keep the unrounded values.
Enter a balanced reaction and known quantity, then select Calculate to see the mole ratio and target result.
target moles = known moles × target coefficient / known coefficient

Calculation method

How the calculation works

Step 1
Convert the known quantity to moles
Amount inputs convert directly. Mass inputs use the formula molar mass, while solution inputs multiply molarity by volume.
Step 2
Apply the equation ratio
Divide known moles by its coefficient to obtain the reaction extent, then multiply by the target coefficient.
Step 3
Convert the target result
Keep the target in moles or multiply by its CIAAW-based molar mass for a mass result.

Worked examples

Check the result by hand

Nitrogen to ammonia
For N2 + 3H2 -> 2NH3, calculate NH3 from 1.00 mol N2.
  1. 1.The known amount is already 1.00 mol N2.
  2. 2.Use the coefficient ratio 2 mol NH3 / 1 mol N2.
  3. 3.Multiply 1.00 mol by 2 / 1.
The reaction amount is 2.00 mol NH3.
Hydrogen mass to water mass
For 2H2 + O2 -> 2H2O, convert 4.032 g H2 to H2O.
  1. 1.H2 has a molar mass of 2.016 g/mol, so 4.032 g is 2.000 mol.
  2. 2.The H2:H2O coefficient ratio is 2:2, giving 2.000 mol H2O.
  3. 3.Multiply by 18.015 g/mol for H2O.
The calculated target mass is 36.03 g H2O.

Scope

Assumptions and limits

These limits keep the result reproducible and make unsupported inputs visible instead of guessing.

The equation must already be balanced. The calculator reports each element whose reactant and product totals differ.
The calculation uses one known species and assumes every other required reactant is available in sufficient excess.
Formula input supports integer subscripts, nested round or square brackets, water hydrate dots, and reaction state labels.
Charged species, isotope notation, decimal subscripts, decimal coefficients, and automatic equation balancing are not supported.
Data and terminology sources: CIAAW Abridged Standard Atomic Weights 2024, IUPAC Gold Book, extent of reaction.

Stoichiometry Calculator FAQ

Frequently asked questions

Does the chemical equation have to be balanced?

Yes. Coefficients define the mole ratio. If element totals differ across the arrow, the calculator lists the imbalance and stops the calculation.

Can I enter grams instead of moles?

Yes. The calculator derives molar mass from the chemical formula, converts the known mass to moles, applies the coefficient ratio, and converts the target when needed.

When should I use the limiting reactant calculator?

Use it when two or more reactant quantities are finite. This page treats unentered reactants as excess and converts one known quantity to one target.