Percent Yield Calculator
In short: Calculate percent yield, actual yield, or theoretical yield with gram, milligram, kilogram, mole, or mmol units. It is free, works in your web browser and needs no download.
Calculate percent yield from actual and theoretical yield, or solve for actual/theoretical yield when percent yield is known.
Percent Yield Formula
- Percent yield: actual yield / theoretical yield × 100.
- Actual yield: theoretical yield × percent yield / 100.
- Theoretical yield: actual yield × 100 / percent yield.
Worked example
You react 5.00 g of salicylic acid (138.12 g/mol) with excess acetic anhydride to make aspirin (180.16 g/mol), and isolate 5.20 g of product.
- Moles of salicylic acid = 5.00 ÷ 138.12 = 0.0362 mol.
- The reaction is 1:1, so the theoretical yield is 0.0362 mol × 180.16 g/mol = 6.52 g.
- Percent yield = 5.20 ÷ 6.52 × 100 = 79.8%.
Why yields fall below 100%
- Product lost during transfers, filtration, or recrystallisation.
- Incomplete reaction or competing side reactions.
- Equilibrium reactions that do not go fully to products.
Why a yield can appear above 100%
A result over 100% usually means the product is impure or wet: residual solvent, water, or unreacted starting material adds mass. Dry the product to constant mass and check purity, for example by melting point or TLC.
Tip: theoretical yield must come from the limiting reagent. If you are unsure which reagent limits, convert every reagent to moles with the Grams to Moles Calculator and compare against the balanced equation.
Last updated: