ChemBench

Limiting Reactant Calculator

Which reactant runs out first?

Dividing moles by the coefficient

Comparing each reactant's moles divided by its balanced-equation coefficient reveals which one would be used up first — that reactant is the 'limiting' one and determines the maximum amount of product possible.

Why it matters in practice

Industrial chemists deliberately use an excess of the cheaper reactant to ensure the more expensive one — the limiting reactant — is fully consumed, minimizing waste of the costly ingredient.

Related Science calculators

Molar Mass Calculator

Molar mass of any chemical formula (e.g. H2O, C6H12O6, Ca(OH)2).

Open

Mass Percentage Calculator

Percent composition of an element within a chemical formula.

Open

Empirical Formula Calculator

Simplest whole-number ratio formula from elemental masses or percentages.

Open

Percent Yield Calculator

Percent yield from actual and theoretical reaction yields.

Open

Loading…

ChemBench

Limiting Reactant Calculator

Which reactant runs out first?

Moles of reactant A

Coefficient of A

Moles of reactant B

Coefficient of B

Limiting reactant

Reactant A

What you entered

Moles of reactant A: 4Coefficient of A: 2Moles of reactant B: 3Coefficient of B: 1

1
Reactant A: moles ÷ coefficient
4 ÷ 2= 2
2
Reactant B: moles ÷ coefficient
3 ÷ 1= 3
3
Smaller ratio is the limiting reactant
min(2, 3)= Reactant A

Result

Limiting reactant: Reactant A

Reactant A runs out first and limits how much product can form.

Dividing moles by the coefficient

Why it matters in practice

Industrial chemists deliberately use an excess of the cheaper reactant to ensure the more expensive one — the limiting reactant — is fully consumed, minimizing waste of the costly ingredient.