How do we know what the capacities of the cremation ovens at Auschwitz-Birkenau were?
Holocaust deniers claim:
There are no authentic German documents that address the capacity of the crematoria ovens in Auschwitz-Birkenau.
The facts are:
There is an authentic letter from Karl Bischoff, the head of the Central Building Administration in Auschwitz-Birkenau, to Hans Kammler in Berlin, which summarized the cremation capacity for the 52 muffles in Auschwitz-Birkenau for a 24-hour period.
David Irving, who the High Court in London in 2000 declared to be a Holocaust denier, racist, and antisemite, asserts that a letter summarizing the ideal cremation capacity for the 52 muffles in Auschwitz-Birkenau in a 24-hour period as 4,756 bodies is a forgery.
The Bischoff letter about the capacities of the cremation ovens at Auschwitz-Birkenau.
A letter, dated June 28, 1943 was sent by Karl Bischoff, the head of the Central Building Administration in Auschwitz-Birkenau, to Hans Kammler in Berlin. It summarized the ideal cremation capacity for the 52 muffles in Auschwitz-Birkenau in a 24-hour period (including down time for cleaning and maintenance):
Crema 1 340 persons
Crema 2 1,440 persons
Crema 3 1,440 persons
Crema 4 768 persons
Crema 5 768 persons
Total per 24 hours 4,756 persons
Bischoff arrived at his figures by assuming that each of the 52 muffles could cremate four bodies an hour, which by definition required multiple cremations at one time.
By Zentralbauleitung Auschwitz, Töpf & Söhne [Public domain], via Wikimedia Commons.
Is the Bischoff letter a forgery?
David Irving argues that the Bischoff letter was forged by the Russians to embarrass the Germans. But the Russians’ own (incorrect) figures for the number of people murdered and cremated in Auschwitz-Birkenau were four times higher than the actual death toll. Why would the Russians forge a letter that confirmed less than one-fourth of their own calculations?
There is an authentic German document about the capacity of the crematoria ovens at Auschwitz-Birkenau: the Bischoff letter (June 28, 1943). The letter details the Germans’ own calculations that the cremation ovens had the ability to burn as at least 4,756 bodies in a 24-hour period.
 Robert Jan van Pelt, The Van Pelt Report (“VI Blueprints of Genocide”) You can see this document at http://www.holocaust-history.org/~dkeren/cremation/Furn-cap.shtml.
 Transcript, Day 32, March 15, 2000 at 27.22. and Robert Jan van Pelt, The Case for Auschwitz: Evidence from the Irving Trial (Indiana University Press, 2001), p. 344. The Russians, for purposes of propaganda against their vanquished enemy, claimed that 4,000,000 people had been murdered at Auschwitz-Birkenau. No mention is made of the Jews—they considered all those who had been murdered were the victims of German fascism. The real mortality figure is closer to 1,100,000, of which some 900,000 were Jews.