The most widely accepted figure is around 20 million.
See related links below. But there is no argument, both Hitler and Stalin where ruthless and blood letting rulers of nations, where the people of those nations were just to frightened to do anything it. Both leaders led a reign of terror over many. Jews, Muslims, Gypsies, Jehovah's Witnesses, even Gays. (There are many other groups that I have not mentioned). Or anyone who tried to stand up against them.
The best way to know or find out about these times, is to chat to some one whom had lived under these times. (From 1930's right up to 1950's) Weather they were in Germany
, Russia (USSR) or Eastern Europe. You will find that there will some that will talk about it. [Survivors can provide accounts of conditions at the time, but when it comes to an actual count of the death toll they are only able to repeat what others have said. The notion that every victim of Stalinist oppression is an expert on the 'big picture' and the overall numbers is absurd. Please use your common sense].
According to the documentary, "Stalin, Portrait of a Monster in Blood." He is estimated to have been responsible for possibly 60 Million Deaths. This is likely an exaggeration, but millions did suffer under his repression.
Look to "Stalin: Triumph and Tragedy" for an excellent portrait of the man by Volkogonov. J Arch Getty's works on Stalin's purges are also an excellent source of information.
There is a vast difference between the number of people Stalin killed in purges and the number that died of neglect and poor conditions in his horrendous network of labour camps which stretched across all of the USSR's 12 time zones. These prisoners of Stalin are largely forgotten in most accounts of Stalin. "Gulag" by Anne Applebaum is the definitive guide on the subject due to her detailed research into both memoirs of prisoners and the NKVD records from the time.
If a dictator has people imprisoned or sent to camps, then he's ultimately responsible for their fate, so there is little distinction between killing people and deliberately letting them die of neglect.
The gap between high and low estimates is enormous. At the upper end one gets estimates ranging from about 40-60 million or even 100 million, at the lower end about 10-20 million. Clearly, there's ideological 'monkey business' at work. Until someone can reconcile these amazing discrepancies satisfactorily, and provide a very clear explanation of how the new figure is arrived at, it's impossible to say how many people Stalin had killed.
During WWII he encouraged tactics which led to the deaths of about 8,000,000 of his own soldiers. Additionally about 2,800,000 German, Hungarian, Romanian, and Finnish troops were killed by his armies. Stalin's policies meant no mercy to prisoners, and huge numbers died after being taken captive during the war. Perhaps 30,000,000 persons of various nations died. Following WWII, Stalin instigated a policy of terror on the German people. This led to about 2,000,000 German civilians being murdered outright and thousands more committing suicide. Stalin enforced brutal police states on all the peoples of eastern Europe which he overran with his armies. Tens of thousands died in these takeovers. German POWs were kept in horrible conditions for as long as ten years after the war, leading to the deaths of at least 1,000,000. In 1945 he launched an unprovoked war with Japan, killing many tens of thousands of Japanese troops and capturing many others.
[Poor military tactics are usually put in a different category. After all, it is
not common to regard the generals of World War 1 as mass murderers on the grounds that they lacked the imagination to break out of trench warfare].
All accounts agree that it is in the millions, perhaps even more than Hitler.
Stalin caused the deaths of people of certain races and nationalities (Jews, Poles, Ukrainians, etc.), people of certain economic status (wealthy farm owners called "kulaks") by relocating them to the gulags (concentration camps) in Siberia where they died of malnutrition, overwork and exposure. He murdered political opponents, actual and suspected, in the thousands usually by a single gunshot to the back of the head. He forced the repatriation of all Russian soldiers taken prisoner during World War 2 and treated them as virtual traitors, sending [many of] them to the gulags as well.
Most accurately, Stalin caused the deaths of at least 20,000,000 people. Obviously, though, he did not kill that many himself. With his faulty tactics and failed techniques on the battlefield, he cause at least 25,000,000 Red Army soldiers. He had several million executed or worked to death in Russia as well.
Some estimates will reach over 60 million, but Stalin is actually only a direct result of 15-20 million deaths. The 5 million difference is from varying estimates due to how many people there was and the secrecy of the USSR.