Limiting Reactant Calculator
Identify which reactant runs out first and how much product it permits.
About Limiting Reactant Calculator
Comparing moles alone is not enough — each must be divided by its stoichiometric coefficient. The smallest result identifies the limiting reactant and sets the extent of reaction. Yield calculations based on the wrong reactant overstate output, and the excess reactant becomes waste that must be separated or disposed of.
Formula
Limiting Reactant
Divide each reactant’s moles by its coefficient; the smallest quotient limits the reaction
- extent of reaction
- How many times the balanced equation proceeds as written
- excess
- Reactant left unconsumed when the limiting one is exhausted
Worked example
With the default values below, Limiting Reactant Calculator returns Limiting Reactant of Reactant A limits the reaction. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Mass of reactant Aminimum 0 g
- 50 g
- Molar mass of Aminimum 0 g/mol
- 2.016 g/mol
- Coefficient of Aaccepts 1–20
- 2
- Mass of reactant Bminimum 0 g
- 400 g
- Molar mass of Bminimum 0 g/mol
- 31.998 g/mol
- Coefficient of Baccepts 1–20
- 1
Results
- Limiting Reactant
- Reactant A limits the reaction
- Moles of A
- 24.801587 mol
- Moles of B
- 12.500781 mol
- Extent of Reaction
- 12.400794 mol
- Mass of Excess Reactant Left Over
- 3.1994 g
Step by step
- 1Values used
- 2Limiting Reactant
- 3Limiting Reactant= Reactant A limits the reaction
- 4Moles of A= 24.801587 mol
- 5Moles of B= 12.500781 mol
- 6Extent of Reaction= 12.400794 mol
- 7Mass of Excess Reactant Left Over= 3.1994 g
Assumptions and limits
- The result is derived only from the 6 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 6 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Limiting Reactant calculated?
Divide each reactant’s moles by its coefficient; the smallest quotient limits the reaction Comparing moles alone is not enough — each must be divided by its stoichiometric coefficient. The smallest result identifies the limiting reactant and sets the extent of reaction.
Why does Limiting Reactant matter?
Yield calculations based on the wrong reactant overstate output, and the excess reactant becomes waste that must be separated or disposed of.
What values do I need to enter?
This calculator takes 6 inputs: Mass of reactant A, Molar mass of A, Coefficient of A, Mass of reactant B, Molar mass of B, Coefficient of B. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.