Chemistry calculator
Percent Yield Calculator
Compare experimental yield with the maximum theoretical yield.
Both yields must use the same unit; theoretical yield must be greater than zero.
Percent yield
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What the two fields mean
"Actual yield" is the amount of product you actually isolated and weighed at the end of an experiment. "Theoretical yield" is the maximum amount that stoichiometry says you could have gotten from your limiting reagent, calculated before you ever ran the reaction. Neither field has a unit dropdown — the calculator treats both numbers as unitless and simply divides one by the other, so it's on you to enter both in the same unit, typically grams.
Actual yield must be zero or greater; theoretical yield must be strictly greater than zero, since it sits in the denominator. If you leave theoretical yield at zero or blank, the result stays empty instead of dividing by zero.
The percent yield formula
An actual yield of 8 g against a theoretical yield of 10 g gives 8 ÷ 10 × 100 = 80%. A messier lab result of 45.2 g actual against 52.0 g theoretical gives 45.2 ÷ 52.0 × 100 = 86.9231%, and the calculator's second line, "Yield lost," reports the complement: (52.0 − 45.2) ÷ 52.0 × 100 = 13.0769%.
When actual yield exceeds theoretical yield, the percentage passes 100% and "Yield lost" turns negative — an actual yield of 11.2 g against a theoretical 10.5 g gives 11.2 ÷ 10.5 × 100 = 106.6667%, with yield lost at (10.5 − 11.2) ÷ 10.5 × 100 = −6.6667%.
Why yields go over 100%, and what the limiting reagent means
Theoretical yield comes from identifying the limiting reagent — whichever starting material runs out first — converting its moles to moles of product using the balanced equation, then converting to grams with molar mass. This calculator only performs the final division step; it doesn't calculate theoretical yield for you, so that stoichiometry has to be done separately before you type a number in.
A percent yield above 100% almost never means more product was created than mass conservation allows. It usually means the isolated solid still contains residual solvent or moisture, unreacted starting material, or an inorganic salt byproduct that wasn't fully separated out — or that the balance or the theoretical-yield calculation itself had an error. Because "Yield lost" is just a subtraction, it displays a negative number in this situation rather than clamping to zero, and that negative sign is itself a signal something needs rechecking.
Percent yield across different reactions
Typical lab results, run through the same formula:
- Aspirin synthesis: 3.20 g actual from 4.10 g theoretical → 3.2 ÷ 4.1 × 100 = 78.0488%
- Isopentyl acetate (banana oil) esterification: 6.5 g actual from 9.8 g theoretical → 66.3265%
- Recrystallized product after removing impurities: 2.1 g actual from 2.6 g theoretical → 80.7692%
- A 1,000 kg industrial batch yielding 950 kg of product → 950 ÷ 1,000 × 100 = 95.0000%
- A Grignard reaction with a slow side reaction: 1.8 g actual from 3.4 g theoretical → 52.9412%
Frequently asked questions
Why do actual and theoretical yield need to be in the same unit?
The formula is a straight ratio of the two numbers you type in — there's no unit conversion happening. Entering one in grams and the other in moles produces a number that looks like a percentage but means nothing, and the calculator has no way to detect that mismatch.
Can percent yield be over 100%?
Yes, and it usually points to a problem rather than a triumph — residual solvent, incomplete drying, unreacted starting material carried through, or an error in the theoretical-yield calculation are the common causes.
Why does a theoretical yield of zero give a blank result?
Theoretical yield is the denominator in the formula, and dividing by zero is undefined. The calculator withholds a result rather than show an error or an infinite value.
What does the "Yield lost" figure show?
It's the complement of percent yield — the share of theoretical product you didn't recover. For 45.2 g from 52.0 g theoretical it reads 13.0769%; when actual yield exceeds theoretical, it goes negative instead, as in −6.6667% for 11.2 g from 10.5 g theoretical.
How do I find theoretical yield before using this tool?
Identify the limiting reagent, convert its moles to moles of product using the balanced equation's mole ratio, then multiply by the product's molar mass in g/mol. This calculator starts after that step — it only divides your actual yield by the theoretical yield you've already worked out.
Is a negative actual yield ever accepted?
No. Actual yield has a minimum of zero, since a negative mass of product isn't physically possible; the field simply won't produce a result if you try to enter one.