About this tool
The Percent Yield Calculator is a free, in-browser chemistry tool that relates the actual yield, theoretical yield, and percent yield of a reaction through % yield = (actual ÷ theoretical) × 100. Leave any one of the three boxes blank and it is solved from the other two, and the tool also reports the complementary percentage lost.
All arithmetic runs locally in your browser, so the yields you enter are never uploaded or stored anywhere. Results update live as you type, making it quick to check a lab result or back-calculate the actual mass you would need for a target efficiency.
The actual and theoretical yields can be in any single consistent unit — grams or moles — as long as both use the same one, because the percentage is a ratio and the units cancel. Percent yield is a dimensionless percentage; values above 100% usually signal impurities or measurement error rather than a real excess.