What is the limiting reagent?

The limiting reagent is the reactant that is completely consumed first, stopping the reaction and determining the maximum amount of product that can form. The other reactant is the excess reagent.

How is the limiting reagent determined?

Divide the moles of each reactant by its stoichiometric coefficient. The reactant with the smallest result is the limiting reagent, because it runs out first relative to what the balanced equation requires.

What is theoretical yield?

Theoretical yield is the maximum mass of product that could form if the limiting reagent were completely converted to product with no losses. It equals (moles of limiting reagent / its coefficient) × product coefficient × product molar mass.

What is percent yield and why is it rarely 100%?

Percent yield = (actual yield / theoretical yield) × 100. It is rarely 100% due to side reactions, incomplete reactions, product lost during purification, or measurement errors.

Can I use equivalents instead of stoichiometric coefficients?

Yes. If you are running a reaction with 1.5 equivalents of Reagent B relative to A, set the coefficient of A to 1 and B to 1.5 (decimals are accepted).

Does this work for reactions with more than two reactants?

This tool handles two reactants producing one product, which covers the vast majority of organic synthesis steps. For three or more reactants, run the calculation in two steps.

Limiting Reagent Calculator

Name: Limiting Reagent Calculator
Availability: InStock
Author: Nham Vu

Enter reactant masses, molar masses, and stoichiometric coefficients to find the limiting reagent, theoretical yield, and percent yield.

A Reactant A

Mass (g)

Molar Mass (g/mol)

Stoichiometric Coefficient

B Reactant B

Mass (g)

Molar Mass (g/mol)

Stoichiometric Coefficient

P Product

Stoichiometric Coefficient

Molar Mass (g/mol)

Actual Yield (g) (optional — for % yield)

Fill in the inputs on the left and click Calculate to see results.

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Summary

Enter reactant masses, molar masses, and stoichiometric coefficients to find the limiting reagent, theoretical yield, and percent yield.

How it works

Enter the mass (in grams) and molar mass of Reactant A.
Enter the mass (in grams) and molar mass of Reactant B.
Enter the stoichiometric coefficients of A, B, and the product from the balanced equation.
Enter the molar mass of the product.
Click Calculate to see the limiting reagent, moles of product, and theoretical yield in grams.
Optionally enter an actual yield to compute percent yield.

Use cases

Determine which starting material to scale up before a multi-step synthesis.
Calculate theoretical yield in grams directly from weighed reagent amounts.
Compute percent yield for a lab report after isolating a product.
Check stoichiometry before running a reaction to avoid wasting expensive reagents.
Plan reaction scale-up for larger batch sizes in process chemistry.
Verify textbook stoichiometry problems with step-by-step breakdown.

Frequently Asked Questions

Last updated: 2026-06-18 · Reviewed by Nham Vu