Using a DC->AC Inverter with a laptop, how many watts are needed?

[SuperFreaky]

I have a Inspiron 600M.

How many watts should I get for an Inverter? It doens't say on the AC Adapter what watts the laptop uses (only volts and amps).


Any place better than RadioShack to get one of these (I need it by tomorrow).
Radio Shack's Power Inverters

 

[sciencewhiz]

watts = volts * amps / 2 (RMS)

 

[SuperFreaky]

u the man sciencewhiz

thanks