About the Limiting Reactant Calculator
Find which reactant runs out first, how much product forms and how much of the excess is left over.
Also known as: limiting reagent, excess reactant, which reactant runs out, limiting reagent calculator.
How to use this calculator
- Enter chemical equation, mass of reactant 1, mass of reactant 2, mass of reactant 3 (optional).
- The result updates instantly as you type — press Calculate (or Enter) at any time.
- Review the breakdown shown under the main result.
- Use Copy result or Share to save the answer or send a link with your inputs.
Formula
The reactant with the smallest moles ÷ coefficient limits the reaction
Worked example
Using the values pre-filled in the calculator above:
- Chemical equation: N2 + H2 -> NH3
- Mass of reactant 1 = 28 g
- Mass of reactant 2 = 10 g
- Mass of reactant 3 (optional) = 0 g
the calculator returns:
- Limiting reactant: N2
- Reaction extent: 0.9995 mol sets
- Balanced equation: N2 + 3H2 → 2NH3
- NH3 produced: 34.045 g