This video shows you how to calculate the percentage yield in chemistry. To find the percentage yield, you will need to divide the actual yield by the theoretical yield. Then, multiply it by 100: i.e. % yield = actual yield/theoretical yield x 100. An actual yield is the amount of a substance produced in an actual laboratory experiment. It is based on an actual physical measurement of a quantity. The theoretical yield is the yield as is calculated on paper: i.e. through calculations. Therefore, for this equation, you would plug in the volume from your lab experiment on top and divide it by the number arrived at through calculations.