Compare what your reaction actually produced against the theoretical maximum. Solve for the percent yield, the actual yield, or the theoretical yield — the calculator rearranges the formula and shows the substitution.
% yield = (actual ÷ theoretical) × 100
Use the same unit (grams or moles) for both yields — the unit cancels in the ratio.
The theoretical yield is the maximum product the limiting reactant allows — a number you calculate. The actual yield is what you weigh after the experiment — a number you measure. Real reactions always deliver less than the theory: side reactions, incomplete conversion and transfer losses all take their cut.
Worked example
A synthesis has a theoretical yield of 51.1 g of ammonia, but the lab isolates 42.0 g. What is the percent yield?
% yield = (42.0 ÷ 51.1) × 100
Answer: ≈ 82% — a perfectly respectable result for a real experiment.
Working backwards
A reaction is known to give a 75% yield. How much product should you expect if the theoretical yield is 20.0 g?
actual = 75% × 20.0 g ÷ 100
Answer: ≈ 15.0 g — useful for planning how much to synthesise.
70–90%: typical for multi-step school and undergraduate experiments.
Below 50%: something is eating your product — incomplete reaction, side products, or losses during filtering and transfer.
Above 100%: impossible. The product is impure (commonly still wet) or a measurement is wrong — recalculate before celebrating.
⚠ Common mistake: Make sure both yields use the same substance and the same unit. Comparing grams of crude product against a theoretical yield in moles (or of a different compound) produces meaningless percentages.
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Frequently asked questions
▸What is the difference between actual and theoretical yield?
Theoretical yield is calculated from the balanced equation and the limiting reactant — the best-case maximum. Actual yield is measured on the balance after the experiment. Percent yield compares the two.
▸Can percent yield be over 100%?
Not genuinely. A value above 100% means the measured product contains something extra — usually residual solvent or impurities — or that a mass or calculation is wrong.
▸How do I find the theoretical yield?
Identify the limiting reactant, then convert its amount to product via the mole ratio. The limiting reactant calculator does the whole chain for any balanced equation.