Limiting Reactant Calculator
Last updated: June 2026 · Free · No sign-up required
Enter values above and click Calculate to see your result instantly.
Quick reference
| Reactant | Moles ÷ coefficient |
|---|---|
| A | moles of A ÷ coefficient of A |
| B | moles of B ÷ coefficient of B |
| Limiting | the reactant with the smaller ratio |
| Excess | the reactant with the larger ratio |
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Below the calculator we link a small set of plain-English explainer pages — "What is a percentage?", "Why does PEMDAS matter?", and so on. They cover the underlying concept in 4–6 short paragraphs. Read those before the calculator if the topic is new, or after if you want the extra context.
Interpretation guide
| Output | What it tells you |
|---|---|
| Limiting reactant | Runs out first and caps the product yield. |
| Excess reactant | Some is left over when the reaction finishes. |
| Ratios | The mole-to-coefficient ratio for each reactant. |
Formula & methodology
Formula: Compare moles ÷ coefficient for each reactant; the smaller ratio is limiting
The limiting reactant is the one that runs out first. Divide each reactant's moles by its balanced equation coefficient; the smallest ratio identifies the limiting reactant.
- Balance the equation and note each reactant's coefficient.
- Enter the moles and coefficient for reactant A and reactant B.
- The calculator computes moles ÷ coefficient for each.
- The smaller ratio is the limiting reactant; the other is in excess.
Worked example: 3 mol A (coeff 1) gives ratio 3; 2 mol B (coeff 3) gives 0.67, so B is limiting.