How this percent yield calculator works
Percent yield tells you how efficient a chemical reaction was by comparing the amount of product you actually collected with the maximum amount the reaction could possibly make. It is one of the most common figures reported in chemistry labs because no real reaction gives a perfect 100% — product is always lost to side reactions, incomplete conversion, transfers and purification.
The calculator takes your actual yield (the product you measured) and your theoretical yield (the maximum predicted by stoichiometry from the balanced equation and the limiting reactant), divides the first by the second, and multiplies by 100. Both values must be in the same units. Because the relationship is simple algebra, you can also leave any one box blank: enter percent yield with theoretical yield to find the actual yield, or percent yield with actual yield to find the theoretical yield.
Reference note: the theoretical yield cannot be zero or negative, because dividing by zero is undefined and a yield must be a positive amount. A percent yield above 100% is physically impossible and usually means the product is impure or still contains solvent — dry and purify, then re-weigh.
Frequently asked questions
- What is percent yield?
- Percent yield is the amount of product you actually obtained from a reaction, expressed as a percentage of the maximum predicted by stoichiometry. It measures how efficient the reaction was — a higher value means less product was lost to side reactions, incomplete conversion or handling.
- How do I calculate percent yield?
- Divide the actual yield by the theoretical yield and multiply by 100: percent yield = (actual yield / theoretical yield) × 100. Both yields must be in the same units. For example, 8 g actual against 10 g theoretical gives 80%.
- What is theoretical yield?
- Theoretical yield is the maximum amount of product a reaction could make if it went to completion with no losses, calculated from the balanced equation and the limiting reactant. It is the denominator in the percent yield formula and comes from stoichiometry, not measurement.
- Can percent yield be over 100%?
- In theory no, because you cannot make more than the theoretical maximum. A value above 100% normally means the product is still wet with solvent, contains impurities, or there is a measurement or calculation error. Drying and purifying usually brings it back below 100%.
- What is a good percent yield?
- It depends on the reaction. In many student labs a yield above about 70–80% is considered good, while some industrial or multi-step syntheses accept much lower. Reactions with side products or difficult separations naturally give lower yields.
- How do I find actual yield?
- Actual yield is the purified product you measure after the reaction, usually by weighing. You can also rearrange the formula: actual yield = theoretical yield × percent yield / 100. So a 10 g theoretical yield at 80% gives an actual yield of 8 g.