Assuming a constant ~240v just use a clamp-on ammeter and multiply the amps by 240. V x I is close enough to the wattage for this application.
Okay, so I got everything set up today and the generator easily turned over my 4 ton variable speed ac system (it does have a KickStart or something installed on heat pump... not sure exactly what they called it... dampens the initial electric kick when it starts.). I could also run my refrigerator and 60" plasma at the same time... AWESOME!
I have everything in my entertainment center running to two power strips... one that has only my TV, Dish Receiver and DVI Switcher and then a second power strip that says "turn off while on generator". that kills the power to all the other unnecessary stuff like computer, security camera hub and other stuff.
ANYWAY, I hooked the amp meter to the black wire within my emergency disconnect (only place I could access it) BUT is just reading that one wire enough? Isn't the white wire hot too? I'm a little confused and uneducated in this area. However based on the math equation you gave me Yoyizit, the ac system running alone was drawing 16amps or 3,840watts. Small price to pay for central air in FL!