Stoichiometry Calculator

How it works

Stoichiometry starts with a balanced chemical equation. Its coefficients give mole ratios, so if the equation is aA + bB → cC + dD, then a reaction extent ξ produces or consumes amounts according to n = coefficient × ξ. This tool converts your entered amount into moles first, then applies those coefficient ratios.

That means the calculator is really a mole-ratio engine with unit conversion built around it. A mass input becomes moles through molar mass, a particle count becomes moles through Avogadro’s constant, and a gas volume becomes moles through the selected molar volume assumption. Once the basis amount is known, every other species can be calculated from the balanced coefficients. If more than one reactant has a known amount, the same framework extends naturally into limiting-reagent logic and theoretical-yield calculations.

• Single-known mode: one known species sets the reaction extent, so every other species can be converted directly from the mole ratio.
• Limiting-reagent mode: when two or more reactants have known amounts, the smallest value of n/coefficient is limiting and controls theoretical yield.
• Percent yield: if you enter an actual product amount, percent yield is (actual ÷ theoretical) × 100%.

Assumptions and formulas

• Mole ratio: n_target = n_basis × (coefficient_target / coefficient_basis)
• Mass conversion: m = n × M, where M is molar mass in g/mol
• Particles: particles = n × 6.02214076×10²³
• Gas volume: V = n × Vₘ using the selected ideal-gas molar volume

Formula-based molar masses use average atomic weights and simple parenthesis parsing. If a label is not a parseable formula, enter the molar mass manually for mass-based conversions.

The page assumes your coefficients already represent a balanced reaction and that the chemistry follows those ratios cleanly. It does not solve equilibrium composition, kinetics, or real-gas deviations. That is why it is best understood as a stoichiometric amount calculator: excellent for balanced-equation arithmetic, but not a replacement for a full thermodynamic or reactor model.

Example workflows

Water formation: for 2H₂ + O₂ → 2H₂O, if you enter 4.00 g H₂ and 32.0 g O₂, both reactants correspond to about 2.00 mol and 1.00 mol respectively, so O₂ is limiting and the theoretical yield is 2.00 mol H₂O or about 36.0 g.

Ammonia synthesis: for N₂ + 3H₂ → 2NH₃, a known amount of N₂ alone can be converted directly to NH₃ by multiplying moles by 2/1.

Gas-volume classroom problems: if all gases are treated ideally at the same reference condition, volume ratios track mole ratios. Choose the correct STP or SATP setting before using gas-volume units.

Frequently asked questions

Do I need to type a fully balanced equation string?

No. This page uses separate rows for each species. Enter the coefficients yourself; that is the balanced equation.

What if a formula cannot be parsed?

You can still use the calculator. Just enter a manual molar mass for any species that uses grams, milligrams, or kilograms.

Can this replace a full real-gas or equilibrium calculation?

No. It is a stoichiometric amount calculator. Gas-volume options use ideal-gas molar volume, and the tool does not model equilibrium, side reactions, or kinetics.

Is my reaction data uploaded?

No. All inputs stay in your browser and are not transmitted by the calculator.