The formula
How to calculate percent yield
Percent yield compares what a reaction actually produced against the maximum the stoichiometry allows. It is the standard measure of how well a synthesis worked.
Theoretical yield is calculated from the limiting reactant, assuming the reaction goes to completion and nothing is lost. Real yields fall short through incomplete reaction, side products, and losses during transfer and purification.
What to enter:
- Actual yield (g)
- Theoretical yield (g)
No submit button: type and the answer moves. Your inputs end up in the link, so the page can be shared already filled in.
The calculation runs on exactly the numbers currently in the fields above, recomputed in full each time — there is no dependency on the order values are entered in, so adjusting one input to test a scenario and then changing it back leaves the result exactly where it started.
Why percent yield matters
The formula behind percent yield is standard and appears in the same form across textbooks and reference material; what a calculator adds is speed and the ability to see instantly how the result responds to a change in any one of the inputs, which is far slower to do by hand.
Beyond a single check, the same calculation is worth rerunning whenever a measured input changes — a new reading, a corrected value, an updated assumption — since the result here always reflects exactly what is currently in the fields above rather than a value calculated once and then left stale.
It is worth remembering that a formula is only ever as good as the assumptions built into it, and most of the standard equations used across science and statistics carry at least one simplifying assumption — a linear approximation, an idealised gas, a normally distributed error term — that holds well in most ordinary cases and breaks down at the extremes. The result here reflects the standard formula exactly; whether that formula's assumptions are appropriate for your particular situation is a separate judgement worth making deliberately rather than assuming automatically.
In practice, a formula like this one is most often reached for at the exact moment a manual calculation needs checking against a deadline — a lab report due, a problem set to submit — which is precisely the situation where a small arithmetic slip is easiest to miss and most costly to leave uncorrected. Running the same inputs through an independent calculator catches that class of error reliably.
Worked example
A concrete run-through, using the values already in the fields:
- Actual yield: 6.8 g
- Theoretical yield: 8.5 g
That gives:
- Percent yield: 80 %
- Product not recovered: 1.7 g
- Loss: 20 %
The figures above are the calculator's own default values, shown purely so the working is visible rather than hidden — the same steps apply exactly to your own numbers, entered in the fields at the top of this page.
Reading the result
Above 90% is excellent for a single step. Multi-step syntheses compound: five steps at 80% each give an overall yield of 33%, which is why long routes are avoided where possible.
Where this goes wrong. A yield above 100% means an error, not a triumph. The usual causes are residual solvent, incomplete drying, or impurities in the product — reweigh after drying to constant mass.
A result that is wrong by an exact factor of ten, a hundred or a similar round number is almost always a units error rather than a mistake in the formula itself — checking each input against the unit stated beside it is the fastest way to track it down.
Above 90% is excellent, 70–90% good, and below 50% suggests something is wrong with the conditions or the workup. Expectations vary widely by reaction type.
Identify the limiting reactant, convert its mass to moles, apply the stoichiometric ratio from the balanced equation, then convert the product moles back to grams.
The headline figure is percent yield. With 6.8 g actual yield and 8.5 g theoretical yield, that comes to 80 %. Change any field and the figure moves with it.
Generally, no more than the least precise input justifies — a result reported to six decimal places from inputs measured to two significant figures is implying a precision the calculation does not actually have. The calculator shows full precision so you can round appropriately for your own use.
Yes — the equation shown in the formula section above is the standard form used in textbooks and reference material for this calculation, not a simplified or approximate version.
Yes, in the sense that it applies the correct standard formula and returns an accurate result for the inputs given — but check your own course or publication's requirements for how results should be rounded, presented and referenced, since those conventions vary and are not something a calculator can know on your behalf.