Grab a cheap USB extension cable (male and female ends), and a cheap multi-meter with mA measuring capability. Slice the sheath of the extension cable somewhere in the middle, but don't break any wires. Get the wires nice and separate, then cut the red wire. Strip both new ends, and put one to each lead of your multi-meter in mA mode. (You can safely hold the exposed wires... its only 5V )
Fire it all up, and look at the reading.
-wk
Don't break any wires is good advice, I wasted an USB cable :p