The standard chemistry lab metric comparing how much product was actually obtained against the maximum amount predicted by stoichiometry.
How it works
Dividing actual yield by theoretical yield and multiplying by 100 gives percent yield.
What this does not include
This does not include calculating the theoretical yield itself from a balanced equation — that figure must be determined separately and entered directly.
How to use this calculator
- Enter the actual and theoretical yield, in the same unit.
A worked example
An actual yield of 8.5 g against a theoretical yield of 10 g → 8.5 ÷ 10 × 100 = 85%.
An actual yield of 12 g against a theoretical yield of 10 g → 120% — above 100%, which can happen with impure product or measurement error.
What the variables mean
| Variable | Meaning |
|---|---|
| Actual yield | The amount of product actually obtained from the reaction |
| Theoretical yield | The maximum possible amount, calculated from the balanced equation |
Edge cases worth knowing
A yield over 100% signals a problem with the experiment, not a better-than-perfect reaction. It usually means the product wasn’t fully dried, or contains leftover solvent or unreacted starting material.
A theoretical yield of zero makes the percentage undefined — there’s no maximum to measure the actual amount against.
Frequently asked questions
Can percent yield exceed 100%?
Yes — this can happen due to impure product, incomplete drying, or measurement error, and reporting it honestly (rather than capping it at 100%) helps identify where a procedure went wrong.
What does a low percent yield indicate?
Losses during the reaction or purification process, side reactions, or an incomplete reaction — all common, expected sources of yield loss in real lab work.
Does the unit of yield matter?
Only that both the actual and theoretical yield are measured in the same unit (like grams) — the ratio itself is unitless.
