Data from Wikipedia.
WWWII deaths:
Russia: 20,000,000 to 27,000,000
UK and colonies: 450,900
USA: 419,400
WWII Military dead:
Russia: 8,668,000 to 11,400,00
UK and colonies: 383,700
USA: 407,300
At the time the population of the US was roughly 3X the UK, and the USSR was roughly 1.4X the US.
edit: I wondered, and found that about 25% of US casualties were in the Pacific theater. http://www.ibiblio.org/hyperwar/USA/ref/Casualties/Casualtie...
What terrible goddam war. Anyway, it's not like the Brits hid in a hole while the Americans saved everyone. No snarky comments at imaginary cocktail parties, please.