Percent Yield Calculator
Find a reaction’s percent yield from the actual and theoretical product masses.
Solves in either direction across eleven mass units, from micrograms to imperial tons.
Updated October 2, 2026
Introduction
You ran a reaction, isolated a solid, dried it, and weighed it. What you have in your hand is the actual yield. What the balanced equation says you could have made is the theoretical yield. The percent yield is simply how much of the second one the first one turned out to be — and that single ratio is what this page calculates, in either direction.
There are three boxes and only one equation between them. Fill in any two and the third is worked out for you: enter the actual and theoretical masses to get the percent yield, enter a target percent yield to get the mass you should be expecting, or enter what you got and how efficient the reaction was to back out what the equation should have produced. Whichever box the calculator fills in for you is highlighted, so you can always see at a glance which number you supplied and which one is the result.
The units cancel out
Percent yield divides one mass of a substance by another mass of that same substance, so the unit is dimensionless. You can weigh your product in ounces and work out your theoretical yield in grams and the answer is still correct — 5.58 lb against 6.54 lb gives the same 85.3211% as 5.58 g against 6.54 g.
Keeping both boxes in the same unit is still worth doing as a habit, though. If the two readings are in different units, a misplaced decimal is very easy to miss.
One thing to have in place first: a balanced equation. The theoretical yield comes from the coefficients in it, so if yours is not balanced yet, start with the chemical equation balancer. If you are starting from scratch and have not worked out the theoretical mass yet, the molar ratio calculator takes a balanced equation and a real quantity of any reactant or product and turns it into masses.
How to Use
Work out the theoretical yield from the equation
Identify the limiting reagent, take the coefficient ratio that produces your product, convert the reactant amount to moles, then multiply by the product's molar mass. The molar mass calculator will give you the product's molar mass if you have its formula to hand but not its mass.
Dry the product, then weigh it
This is the actual yield, and it is the only number in the whole calculation that depends on your technique. Weigh it before it is fully dry and you will report a yield that is too high, because the solvent comes off the balance along with the water.
Enter any two of the three boxes
Both masses default to grams, and each has its own unit menu running from micrograms to imperial tons. The percent yield box takes a plain percentage. Whichever box you leave empty is the one that gets calculated.
Worked example: 5.58 g from a 6.54 g theoretical yield
Enter 5.58 in Actual yield and 6.54 in Theoretical yield. The percent yield fills itself in:
Reported to four decimal places. The full value carries far more digits than that, and the calculator keeps them internally.
Reading Your Result
A percent yield is a measurement of a specific reaction on a specific day, so the useful reading is not the number itself but what it tells you about where the material went.
- Below 100% is the normal outcome. Product is lost at every transfer, some reactant never converts, and a film of solid stays stuck to the glassware. There is no single “good” number — repeatability across your own runs is the thing worth improving.
- Exactly 100% is not a realistic result. Something always remains behind in the mother liquor or on the glass.
- 0% is a legitimate answer and an informative one: nothing was recovered. The calculator shows it as a plain result rather than an error.
A yield above 100% is a drying problem, not a maths problem
You cannot create matter, so a percent yield above 100% means the solid you weighed is carrying something else. The usual culprit is solvent or water that has not been driven off, and sometimes unreacted starting material that was never removed.
For example, isolating 122.1 g where the equation predicted 100 g gives a percent yield of 122.1% — accepted quietly by the calculator, because wet product really does read that way.
Anything above 200% is a different situation, because it would mean the solid outweighs twice its own expected mass. The calculator keeps the number on screen but marks it in red, since at that point the weighing or one of the two masses is more likely wrong than the product being extraordinarily pure.
If you know the efficiency you are aiming for and want to know what that should weigh on the balance, work the relationship the other way round with the actual yield calculator: it multiplies a theoretical mass by a percent yield directly, which is the one direction this page deliberately does not duplicate.
Calculation Method
All three boxes are bound to one proportion, which is why any two of them are enough to determine the third.
Percent yield from two masses
is the mass you isolated and weighed, is the mass the balanced equation allows for.
Mass to expect from a target yield
Use this when you know the efficiency you are aiming for and want to know what to expect on the balance.
Theoretical yield from what you recovered
This is the useful one when a published procedure quotes a percent yield and you want the mass it started from. A percent yield of zero leaves nothing to divide by, so this box stays blank and tells you so rather than reporting a meaningless number.
The arithmetic is carried out at full decimal precision rather than in binary floating point, so a ratio that looks like it should repeat — 5.58 ÷ 6.54 is 0.8532110091743119… — is not truncated before the result is rounded for display. That matters when you are comparing two runs that differ in the third decimal place.
Tips & Best Practices
Dry to a constant mass
Heat, cool, re-weigh, and repeat until two weighings in a row agree. A product weighed while still cooling picks up moisture from the air, which pushes the percent yield above its true value.
Do not round-trip a rounded percent
Feeding 85.3211% back into the calculator gives a theoretical yield of 6.5400001 g, not 6.54 g — the four displayed decimals are a preview of a longer value. The discrepancy is tiny, but it is the kind of thing that gets quoted onward as if it were meaningful.
Match both masses to the same unit
Not required, but it makes a decimal-point slip immediately obvious. A theoretical yield left in milligrams and an actual yield typed in grams will return a plausible-looking percentage that is wrong by a thousand.
Weigh the product, never the crude
A percent yield is only as good as the purity of what went on the balance. Crude oil, wet cake and unfiltered precipitate will all produce a confident number that describes none of your actual product.
Limitations
- •This page divides two masses. It does not balance equations, work out limiting reagents, or do any stoichiometry — the theoretical yield has to come from your own analysis.
- •It has no view on purity. A percent yield is a ratio, so it cannot tell you whether your solid was pure, only how heavy it was for the amount of starting material you used.
- •It does not explain why a yield came out low. Transfers, side reactions, incomplete conversion, product loss on glassware and recovery losses from recrystallisation all land in the same single number, so the figure has to be interpreted alongside your notes.
- •A theoretical yield of zero is rejected rather than divided by. That is the right call — a ratio to zero is undefined — but it means this page cannot help you diagnose a reaction that was never going to make product.
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