This online calculator illustrates concept of commission as of "a payment to someone who sells goods that is directly related to the amount sold" (according to Cambridge Dictionary). A commission is related to the sale price via the commission rate, usually expressed as percentage. You can find all formulas below the calculator.
How to calculate Commission
Using this relation we can also find sale price if we know commission and commission rate
and commission rate if we know sale price and commission
Of course, if you use percents, you should divide rate in percents by 100 if you use it in calculations, or multiply it by 100 if you want to get percents back as a result.