Casualties
The Russian casualties in the First World War are difficult to estimate, due to the poor quality of available statistics. Some official Russian sources list 775,400 battlefield fatalities. More recent Russian estimates give 900,000 battlefield deaths and 400,000 dead from combat wounds, or a total of 1,300,000 dead. This is about equal to the casualties suffered by France and Austria-Hungary and about one-third less than those suffered by Germany.
Cornish gives a total of 2,006,000 military dead (700,000 killed in action, 970,000 died of wounds, 155,000 died of disease and 181,000 died while POWs). This measure of Russian losses is similar to that of the British Empire, 5% of the male population in the 15 to 49 age group. He says civilian casualties were five to six hundred thousand in the first two years, and were then not kept, so a total of over 1,500,000 is not unlikely. He has over five million men passing into captivity, the majority during 1915.
When Russia withdrew from the war, 3,900,000 Russian POWs were in German and Austrian hands. This by far exceeded the total number of prisoners of war (1,300,000) lost by the armies of Britain, France and Germany combined. Only the Austro-Hungarian Army, with 2,200,000 POWs, came even close.
Read more about this topic: Eastern Front (World War I)