Percent Yield
Compare the amount you actually made with the theoretical maximum to score a reaction’s efficiency.
8 g obtained of 10 g possible.
Percent yield is the actual yield divided by the theoretical yield, times 100: % yield = (actual ÷ theoretical) × 100. If a reaction gives 8 g of product when the theoretical maximum is 10 g, the percent yield is (8 ÷ 10) × 100 = 80%. Both amounts must share the same unit.
What percent yield measures
Percent yield rates how efficient a reaction was — how much product you actually recovered compared with the most you could possibly make. The theoretical yield is that maximum, calculated from the balanced equation and the limiting reagent. The actual yield is what you weigh out at the bench after the reaction and any purification. Dividing one by the other and scaling to 100 turns the comparison into a clean percentage.
Actual and theoretical yield must be in the same unit (g or mol).
Worked example
A synthesis has a theoretical yield of 10 g, but you isolate only 8 g of pure product. Find the percent yield.
- 1 Find the theoretical yield. From the balanced equation and limiting reagent, the most product you can make is 10 g.
- 2 Measure the actual yield. After the reaction and purification, you weigh 8 g of product.
- 3 Divide actual by theoretical. 8 g ÷ 10 g = 0.8 — the two grams cancel, leaving a pure ratio.
- 4 Multiply by 100. 0.8 × 100 = 80%, so the reaction ran at 80% efficiency.
Reading a percent yield
Rough guidance — acceptable yields vary widely by reaction type and scale.
| Percent yield | Interpretation |
|---|---|
| 90–100% | Excellent — efficient reaction with little loss |
| 70–90% | Good — a typical strong result for many syntheses |
| 50–70% | Moderate — some product lost to side reactions or workup |
| Below 50% | Low — significant loss; review method or limiting reagent |
| Above 100% | Impossible — product is impure or a measurement is off |
Where the numbers come from
Theoretical yield is calculated, not measured. You get it from stoichiometry: balance the equation, find the limiting reagent, and convert its moles into the maximum moles — then grams — of product. The limiting reagent calculator and stoichiometry calculator handle that step.
Real yields fall below 100%. Product is lost to incomplete reactions, competing side reactions, and transfers during filtering, washing, and drying — so the actual yield is normally less than the theoretical maximum.
A yield above 100% signals a problem, not a triumph. You cannot create more product than the reactants allow. A result over 100% means the weighed product still contains solvent, water, or unreacted starting material, or that the theoretical yield was miscalculated. Dry and purify the sample, then reweigh.