ChemBench

Percent Yield Calculator

How close did the reaction get to perfect?

Actual yield (g)

Theoretical yield (g)

Percent yield

90 %

% yield = actual ÷ theoretical × 100

What you entered

Actual yield (g): 18Theoretical yield (g): 20

1
Percent yield = actual ÷ theoretical × 100
18 ÷ 20 × 100= 90%

Result

Percent yield: 90 %

Getting 18g out of a theoretical 20g is a 90% yield.

Percent yield from actual and theoretical mass

Percent yield is actual yield divided by theoretical yield, times 100. It measures how much of the possible product you actually recovered.

Actual yield	Theoretical yield	Percent yield
9.1 g	12 g	75.8%
4.2 g	5 g	84.0%
8.5 g	10 g	85.0%
22.4 g	25 g	89.6%
45 g	50 g	90.0%
95 g	100 g	95.0%

A yield above 100% means the product is wet or impure, not that the reaction overperformed. Typical undergraduate lab yields land between 60% and 90%.

Reality vs. the theoretical maximum

Percent yield compares what you actually collected in the lab (actual yield) to what stoichiometry predicts is the maximum possible (theoretical yield) — real reactions almost never hit 100% due to side reactions, incomplete reactions, or product lost during purification.

Why it's a key lab metric

Percent yield is one of the standard ways chemistry labs and industrial processes are graded — a consistently low yield signals a technique or process problem worth investigating.

Frequently asked questions

I expected 25 g of product but only got 18 g — what is my percent yield?

Percent yield = (actual/theoretical) × 100 = (18/25) × 100 = 72%. That is a reasonable yield for many organic reactions.

How is percent yield different from theoretical yield?

Theoretical yield is the maximum grams of product possible (calculated from stoichiometry via the theoretical yield calculator). Percent yield compares what you actually collected to that maximum — it is a measure of efficiency, not quantity.

Can percent yield ever exceed 100%?

In theory no, but in practice you sometimes measure over 100% due to impurities, incomplete drying, or side products contaminating your collected sample. A yield above 100% signals the product needs further purification.