Percent yield formula
Percent yield compares what you actually made to the maximum possible: %yield = (actual ÷ theoretical) × 100. The theoretical yield is the mass predicted by stoichiometry. To estimate experimental accuracy, see the percent error calculator.
How to use this calculator
Enter the actual yield (the mass you measured after the reaction) and the theoretical yield (the maximum predicted). Both must be in the same unit, usually grams. To convert masses to moles for stoichiometry, use the moles calculator.
- Base the theoretical yield on the limiting reagent, not on whichever reactant you happened to weigh.
- Dry the product first. Residual solvent is the usual cause of yields above 100%.
- Same units on both lines — mixing grams and milligrams is an easy slip.
Worked example
A reaction should produce 10 g of product but you isolate only 8 g. Percent yield = 8 ÷ 10 × 100 = 80%. Losses during filtering and transfer are common reasons yield falls below 100%.
What counts as a good yield depends on the chemistry. A simple precipitation might routinely hit 90–95%, while a multi-step organic synthesis can be respectable at 40%, and losses compound across steps — three consecutive 80% steps leave only 0.8³ ≈ 51% overall. Tracking percent yield over repeated runs is one of the fastest ways to spot a procedure that has quietly gone wrong. A low yield sometimes reflects impure starting material, which the mass percent calculator can quantify.
Frequently asked questions
- What is percent yield?
- It is the ratio of the actual product obtained to the theoretical maximum, expressed as a percentage.
- Can percent yield exceed 100%?
- It shouldn't in theory. Values above 100% usually mean impurities or leftover solvent inflated the actual mass.
- What is theoretical yield?
- The maximum product mass predicted by the balanced equation if the reaction were perfectly efficient.
- Why is real yield below 100%?
- Side reactions, incomplete reactions, and product lost during purification all reduce the actual yield.
- How do I predict the mass I will get from a target percent yield?
- Multiply the theoretical yield by the percent yield as a decimal. If a reaction usually runs at 80% and the theoretical yield is 10 g, expect about 10 × 0.80 = 8 g of product.