When purifying a substance in chemistry, use (collected mass/starting mass)*100 to calculate percent recovery. This formula is also commonly stated as (pure product recovered/crude material used)*100.
Percent recovery is used when there is no chemical reaction taking place and a substance is simply purified, such as through evaporation or crystallization. When a chemical reaction is taking place, the percent yield formula is used. To ensure a correct result, verify that the units of measure used for both starting and collected mass are consistent, and make sure that the product does not contain any other substances, such as water or other solvents.