Limiting Reagent Calculator
Enter two reactants and the balanced equation coefficients to find which one runs out first.
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Limiting reagent
Limiting reagent
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Theoretical yield of product (g)
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Excess reactant left over (g)
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Moles of A
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Moles of B
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Limiting Reagent Calculator by TheCalcTools
How the Limiting Reagent Calculator works
Divide each reactant’s moles by its coefficient in the balanced equation. The smaller result belongs to the limiting reagent: it runs out first and sets how much product forms.
The excess reactant is what remains after the reaction uses the amount matched to the limiting reagent.
The formula
Limiting = smaller of (n_A ÷ a) and (n_B ÷ b); product = that value × product coefficient × M_product
Worked example
Using the default values shown in the calculator:
| Mass of reactant A (g) | 50 |
|---|---|
| Molar mass of A (g/mol) | 26.982 |
| Coefficient of A | 4 |
| Mass of reactant B (g) | 50 |
| Molar mass of B (g/mol) | 31.998 |
| Coefficient of B | 3 |
| Coefficient of product | 2 |
| Molar mass of product (g/mol) | 101.96 |
- 4 Al + 3 O₂ → 2 Al₂O₃. Al: 1.853 mol ÷ 4; O₂: 1.563 mol ÷ 3.
- Limiting reagent: A. Theoretical yield 94.47 g of Al₂O₃, with 5.53 g of excess left.
Result:
| Limiting reagent | A |
|---|---|
| Theoretical yield of product (g) | 94.470 |
| Excess reactant left over (g) | 5.529 |
| Moles of A | 1.8531 |
| Moles of B | 1.5626 |
Frequently asked questions
Is the limiting reagent the one with the smaller mass?
Not necessarily. What matters is moles compared with the coefficients in the balanced equation.
Sources and further reading
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.