Limiting Reactant Calculator

The limiting reactant is the one that runs out first — it caps how much product can form. For each reactant, divide its available moles by its balanced-equation coefficient; the smaller 'capacity' belongs to the limiter, and this tool also reports how much of the other reactant is left over.

How to interpret the result

Worked check: 2H₂ + O₂ → 2H₂O with 5.0 mol H₂ and 2.0 mol O₂. Capacities: H₂ = 5.0/2 = 2.5, O₂ = 2.0/1 = 2.0 — O₂ is limiting. Excess H₂ = 5.0 − 2.0×2 = 1.0 mol. If an 'excess' comes out negative, you picked the wrong limiter.

Assumptions

• The equation is balanced and the reaction goes to completion
• No side reactions consume the reactants