Easy way: Turn on the zebras (at 100 IRE), point the camera at an evenly lit white surface, and iris down until the zebras just disappear on the white surface. Then, meter it, and adjust the iso on your meter until the aperture on the meter reading matches the one set on the camera.
Accurate way: hook the camera up to a waveform monitor, and point it at an evenly lit white card. Iris down until the highlights hit 100 IRE on the waveform, and then meter until your meter reading matches your iris on the camera.
Really Easy way (especially if oyu don't have a meter): Look on google, someone has probably figured it out already, but sometimes you get different numbers. See what most people seem to agree on.