Numbers are a poor way of reckoning the immense cost, but here's some typical GW death figures. MIAs may or may not be included.
Germany 1.7 million (65% total casualties of forces engaged)
Russia 1.7 million (76%)
France 1.3 million (73%)
Austria-Hungary 1.2 million (NINETY percent)
Brit Empire 900,000+ (35%)
Italy 650,000 (39%)
Romania 335,000 (71%)
Turkey 325,000 (34%)
USA 116,000 (7%)
Worldwide total: 13.6 million known dead, 33 million WIA, 12 million MIA/POW.
Allies 52% total casualties, Central Powers 67%. Overall 57%.
The Great War . Resources . WWI Casualties and Deaths | PBS