Percent Yield Calculator
Actual yield over theoretical yield, as a percentage — with the over-100% honesty note.
What is Percent Yield?
Percent yield is actual ÷ theoretical × 100 — the fraction of the ceiling the experiment reached. The two amounts must be in the same unit, because the ratio is what survives and the unit cancels. A result over 100% is not a triumph and not capped: it means wet product, a side product weighed along with it, or a measuring error, and the page says so rather than quietly normalising the number.
How it works
One division, in grams or moles — the unit is a selector and cancels in the ratio. The page reports the yield, the amount lost to the reaction, and where losses actually go: side reactions, purification, product left on the glassware. Above 100%, the note names the usual causes and suggests drying and re-weighing instead of treating the number as fine.
- Enter what you know. Every field recalculates as you type — there is no submit button. Leave the quantity you want blank and the page solves for it.
- Read the answer and the working. The result appears above the fold; underneath it is the formula with your numbers substituted, so the arithmetic can be checked rather than trusted.
- Check the units and the size. Units are shown on every value and selectable per field, so a result in kJ, kPa or km/h is converted rather than assumed. Sanity-check the magnitude against a known landmark such as 1 g/cm³ for water.
Examples
A textbook problem with a known answer
Every tool here is checked against standard example problems — the molar mass of C6H12O6 is 180.16 g/mol, and free fall from 20 m takes about 2.02 s at g = 9.8 m/s².
A result you want to reason backwards from
Leave the quantity you already know blank instead: given the final answer, most tools recover the starting value — the mass needed for a target concentration, or the height a fall must have had.
Common mistakes
Forgetting that a formula is only as good as its subscripts
H2O and H2O2 are different compounds. The formula field shows its parse — element by element — so a mis-typed subscript is visible before it reaches the arithmetic.
Mixing units in the middle of a calculation
The most common source of a wrong answer is a value in grams next to a formula expecting kilograms, or Celsius next to a gas constant expecting kelvin. This category converts on the way in and labels what it used.
Frequently asked questions
What is a good percent yield?
For teaching labs, 60–90% is ordinary and above 90% is excellent; research synthesis often lives lower. The honest comparison is against the theoretical yield of the same reaction — which the Theoretical Yield Calculator computes — rather than against a classmate's.
My yield is over 100%. Do I just write it down?
No. The most common cause is product that is still wet — solvent adds mass that was never product. Dry it to constant mass and weigh again. If it is still over 100%, a side product or an impurity is in the weigh boat, and the measurement — not the chemistry — is what failed.
Can I mix grams and moles?
No. Both amounts must be in the same unit — the tool offers grams or moles as a selector for exactly this reason. A gram figure against a mole figure is not a ratio, it is a typo.