TL;DR version: Between 442 462 and 1 245 450 people in all countries of the Eastern Front.
Warning: I believe a bad estimate is better than no estimate at all and I'm aware of the flaws of this "method". If you know a better one, I'm all ears. Maybe you can take these calculations and improve them.
Miriam Gebhardt writes in her book Als die Soldaten kamen: Die Vergewaltigung deutscher Frauen am Ende des Zweiten Weltkrieges (German, "When the soldiers came: Rapes of German women at the end of World War II) that
- at least 190 000 German women were raped by American troops (positions 60 and 459 of 5321 in the Kindle edition of the book above),
- 50 000 by the French (pos. 459),
- 45 000 by the British,
- 15 000 by the Soviets and
- 10 000 by the Belgians.
We can estimate the number of rapes per soldier. The author of that book writes that the maximum number of troops stationed in Germany was, at its peak,
- 600 000 for US (beginning of 1946, pos. 312 of 5321) and
- 400 000 for the British (pos. 325 of 5321).
No data is available in the book for the French and Belgians. The data for the Soviets (1 500 000 in 1945, 800 000 in 1949) is available, but looks suspicious to me (reason see below).
From these data we can calculate the estimate of rapes per soldier:
- 190 000 rapes / 600 000 troops = 0,3167 rapes per soldier
- 45 000 rapes / 400 000 troops = 0,1125
For the Soviets that estimate would be an order of estimate lower, which doesn't look believable to me.
If we assume that the Germans in the Soviet Union raped with roughly the same intensity as the Americans and the British in Germany, we can get an estimate by multiplying rapes per soldier by the strength of the German troops in the Soviet Union. This assumption can be justified by the claim that ideas about sexual violence at war used by the Nazis and the Allies were similar: Regina Mühlhäuser writes in her paper Eine Frage der Ehre. Anmerkungen zur Sexualität deutscher Soldaten während des Zweiten Weltkriegs (German; "A question of honor // Notes about the sexuality of German soldiers during World War II"):
In the middle of the 20th century Göring's argumentation was in
accordance with the values and norms system in Europe and the
In 1946 [acts of sexual violence] were considered by the Allies not as a
crime to be punished, but as a natural
side effect of the war.
According to Wikipedia there were 3 933 000 German troops on the Eastern Front.
This results in following estimates of German rapes in the Soviet Union, Poland, Czechoslovakia, Yougslavia (and other German adversaries on the Eastern Front):
- 3 933 000 troops * 0,3167 rapes per American soldier = 1 245 450 rapes
- 3 933 000 troops * 0,1125 rapes per British soldier = 442 463 rapes
For comparison: According to Miriam Gebhardt, 860 000 German women were raped between 1945 and 1955 in all Germany (Eastern and Western), by all occupational powers.