Percent Yield Calculator — reaction efficiency

How it works

Chemical reactions rarely produce every last bit of product that the balanced equation predicts. Percent yield compares what you actually got to that theoretical maximum (OpenStax Chemistry):

Percent yield = (actual yield ÷ theoretical yield) × 100

The theoretical yield is the amount of product calculated from the stoichiometry of the reaction and the limiting reactant — the most you could possibly make. The actual yield is what you recover in practice, which is usually less because of side reactions, incomplete reactions, and losses during transfer and purification. Both must be in the same units (grams or moles) so the units cancel and the result is a pure percentage.

A percent yield near 100% means an efficient, clean reaction; a low value flags product loss or a side reaction competing for the reactants. Values slightly above 100% usually signal a problem — often an impure or still-wet product weighing more than the pure substance would.

Worked example

A reaction with a theoretical yield of 10 g that actually produces 8.5 g:

Percent yield = (8.5 ÷ 10) × 100 = 85%

Recover all 10 g and the yield is 100%; recover 5 g and it drops to 50%.

Frequently asked questions

How do you calculate percent yield?

Divide the actual yield by the theoretical yield and multiply by 100. For 8.5 g actual out of 10 g theoretical, that is 85%.

What is the difference between actual and theoretical yield?

Theoretical yield is the maximum product predicted by the reaction's stoichiometry. Actual yield is the amount you really obtain, which is normally lower due to losses and side reactions.

Can percent yield be more than 100%?

It shouldn't be. A value above 100% almost always means the measured product is impure or contains leftover solvent or water, making it weigh more than the pure product would.

Why is percent yield usually less than 100%?

Because some product is lost to incomplete reactions, competing side reactions, and unavoidable losses when transferring and purifying the product.

What units should I use?

Any, as long as the actual and theoretical yields use the *same* unit — grams and grams, or moles and moles. The units cancel, leaving a percentage.

How do I find the theoretical yield?

Use the balanced equation and the limiting reactant: convert the limiting reactant to moles of product with the mole ratio, then to mass with the product's molar mass. That maximum is the theoretical yield.