About this percent yield calculator

PercentYieldCalculator.org is a small set of chemistry calculators built around one question: how much of a reaction actually made it to the flask. The percent yield calculator is the main tool, and the 22 supporting pages each cover one step that feeds into it.

It exists because most yield calculators return a number and stop. They round to two decimals whatever your data, they accept a result above 100% without comment, and they never show the substitution that produced the answer. Those are the three things this build sets out to fix.

How the numbers are checked

Every calculation runs against an automated test suite before it ships. The suite drives the same code the browser runs rather than a copy of it, and covers 70 cases: the worked examples, the edge cases of zero, negative, blank and decimal inputs, values spanning 10⁻¹² to 10⁹, unit conversion in both directions, and each refusal message.

Worked examples are checked for chemistry as well as arithmetic. A widely copied example elsewhere has calcium carbonate reacting with acetic acid to give acetone, which is not a reaction that happens. The examples here use reactions that do, with molar masses taken from the IUPAC standard atomic weights.

Two things you will not find here

• Invented numbers. No user counts, no testimonials, no star ratings. Nothing that cannot be verified is claimed anywhere on the site, and nothing of that kind appears in the structured data either.
• Controls that do nothing. Every field, dropdown and toggle changes the result. Nothing renders as a placeholder for a feature that does not work yet.

Significant figures

Results follow the convention for multiplication and division, so the answer carries the fewest significant figures present in the inputs. Two floors apply, three figures on a percentage and two on a mass, so an answer never loses a whole digit. The unrounded value is always shown underneath, and the rounding can be switched off.

This is why an answer here can differ in the last digit from another calculator. The difference is the rounding convention, not the arithmetic.

References

1. Furniss, B. S.; Hannaford, A. J.; Smith, P. W. G.; Tatchell, A. R., Vogel's Textbook of Practical Organic Chemistry, 5th ed., Longman Scientific & Technical, 1989, pp. 33 to 34.
2. Ramsden, E. N., Calculations for A-level Chemistry, Thornes, 1995, p. 38.
3. IUPAC, Compendium of Chemical Terminology (the Gold Book), 2nd ed., entries for yield and limiting reagent.
4. IUPAC Commission on Isotopic Abundances and Atomic Weights, standard atomic weights, 2021 revision.

Corrections

If a result here disagrees with your own working, that is worth reporting. Send the two numbers you entered and the answer you expected through the contact page and the working gets checked by hand. Anything that turns out to be a genuine error is fixed and added to the test suite so it cannot come back.