It remains unknown but I have some data that may be helpful:
The Soviet Union lost the most with 25 million deaths, but only about a third were combat related.
China's death toll is incomplete but estimates are between 15 and 22 million.
Poland had 6 million deaths including 3 million Jews, roughly 20% of its prewar population.
Germany lost 4 million soldiers and 2 million civilians, many of them women.
Japan had 1.2 million battle deaths and another 1.4 million soldiers listed as missing, almost 1 million civilians were killed in the bombing raids between 1944 and 1945.
Over 1.7 million Yugoslavs and 500,000 Greeks died in the war.
France lost 200,000 soldiers and 400,000 civilians.
Italy lost 330,000 people.
Hungary lost 147,000 men in combat.
Bulgaria lost 19,000 in combat.
Romania lost 73,000 in combat.
Great Britain lost 264,000 soldiers and 60,000 civilians in bombing raids.
The United States lost 292,000 soldiers.
The Dutch lost 10,000 soldiers and 190,000 civilians.
Australia lost 23,000 men in combat.
Canada lost 37,000 soldiers.
India lost 24,000 men in battle.
New Zeland lost 10,000.
South Africa lost 6,000.
These totals do not include the 6 million Jews who perished in the Final Solution of Nazi Germany or the 17 million dead as a result of Japan's policies in Asia from 1931 to 1945.
http://wiki.answers.com/Q/How_many_soldiers_died_in_World_War_2
