How to derate PWM current measurement?

[iXod]

If I know the duty cycle of the pure pulsed DC voltage, and my AC/DC RMS clamp meter tells me it sees 20 amps, is there a direct relationship between duty cycle and true current I can use to know the real current? (Frequency is unknown but this shouldn't be a factor as long as it is within the specifications of the meter.)

For example, I know that for 50 percent duty cycle it's common knowledge that real current is 10 percent above measured. Likewise, is there a known relationship for other duty cycles?

It is inconvenient to measure "directly" using a shunt, so a clamp meter is my only option right now.

Thanks.