Is there a direct formula for calculating the voltage from a PWM circuit?

say I had a PWM chip controlling a FET with X volts feeding the FET, is there a direct calculation?

I work better with real numbers and felt using real numbers would result in people thinking I'm asking a homework problem, however, using whole numbers would be easier.

Say 10 volts at the drain and 100kHz at the gate, what would I get out (assuming there is a direct calculation).

Thanks in advance.