explode.
it's the same formula, but as the AC voltage fluctuates (and changes sign) the wattage of an AC device is the average wattage of the device measures at each point over the entire AC cycle.
I don't think I esplained that well...
AC watts = f * ?(theta 0->2pi) V*A (d theta)
that's probably clear as mud too,
see this page:
yeah.