Percent Yield Calculator with Limiting Reactant

How to use it

Type the Reactant A mass and its Reactant A molar mass, and its Reactant A coefficient from the balanced equation.
Add reactant B in the same way, or leave its Reactant B mass empty for one reactant.
Type the Product molar mass, its Product coefficient and the Actual mass of product you obtained.
Read the Percent yield, the Theoretical yield and the Limiting reactant, then follow How the yield is worked out.

How the percent yield is found

The percent yield compares the mass of product you obtained with the mass that the balanced equation predicts. The predicted mass is the theoretical yield, and it is set by the limiting reactant, the reactant that runs out first. The mass you obtain is called the actual yield.

Each reactant's moles are its mass divided by its molar mass. Dividing the moles by the coefficient in the balanced equation shows how much product that reactant could make, and the smaller value is the limiting reactant.

percent yield = actual yield ÷ theoretical yield × 100 %
n = m ÷ M
per coefficient = n ÷ coefficient (the smaller value is limiting)
theoretical yield = per coefficient × product coefficient × M of product

The coefficients matter: in 2 H2 + O2 → 2 H2O, two moles of hydrogen react with one mole of oxygen to give two moles of water.
A percent yield above 100 % means the numbers do not match the reaction, or the product was not dry.

What the calculator does not cover

It does not balance the equation. Use the coefficients of a balanced equation.
It takes one or two reactants and one product. A reaction with more reactants or products needs its own calculation.
It does not work out molar masses from formulas. Use the molar-mass tool, or type the value from a periodic table.

Worked example: 4.00 g H2 and 32.00 g O2, with 30.0 g of water

The balanced equation is 2 H2 + O2 → 2 H2O, so the coefficients are 2, 1 and 2. The molar masses are 2.016 g/mol for H2, 31.998 g/mol for O2 and 18.015 g/mol for H2O. Reactant A gives 4.00 ÷ 2.016 = 1.9841 mol, which is 0.9921 per coefficient. Reactant B gives 1.0001 per coefficient. The smaller value is reactant A, so H2 is limiting.

The theoretical yield is 0.9921 × 2 = 1.9841 mol of water, and 1.9841 mol × 18.015 g/mol = 35.74 g. The percent yield is 30.0 g ÷ 35.74 g × 100 = 83.9%.

Quantity	Value
Moles of reactant A (H2)	1.9841 mol
Moles of reactant B (O2)	1.0001 mol
Limiting reactant	Reactant A
Theoretical yield of water	35.74 g
Percent yield	83.9%

Frequently asked questions

What is the limiting reactant?

It is the reactant that runs out first, and so limits how much product can form. Find it by dividing each reactant's moles by its coefficient in the balanced equation; the smaller result is the limiting reactant.

Why is my percent yield above 100 %?

A value above 100 % means the product mass is more than the theoretical yield. The usual causes are a wrong molar mass or coefficient, or a product that still holds water or solvent when it was weighed.

Do I need the coefficients?

Yes. The coefficients tell how many moles of each substance react together, so without them the calculator cannot tell which reactant runs out first. Take them from a balanced equation.

Where do I get the molar masses?

Add the standard atomic weights of the elements in the formula, each multiplied by its number of atoms. The molar-mass tool does this for you, and the default values here use the IUPAC standard atomic weights for hydrogen and oxygen.

What is a good percent yield?

The percent yield depends on the reaction and the method, so there is no single good figure. Compare your value with the yield your procedure or your textbook gives for the same reaction.

Can I enter the masses in kilograms?

The boxes take grams, and the molar masses in grams per mole. If you have kilograms, multiply by 1000 first, or enter both the mass and the molar mass in the same unit so the ratio is right.

Sources

Figures and text last checked on Thursday, November 12, 2026.

Result

How the yield is worked out