well I once tried doing the math using only official sources for the death tolls of all concentration camps. See:
If 1.1 million people were killed in Auschwitz, 800k in Treblinka, 167k in Sobibor, 200k in Chelmno/Kulmhof, 80k in Majdanek, 500k in Belzec and 60k in Maly-Trostenets this amounts to only a total of 2.9 million people.
These were all the death/extermination camps in Poland, btw.
If you add in the victims of all other concentration camps where no large scale (50k and more) gassings took place, and people mostly died out of other causes like disease, attrition and firing squads for disobeying orders, I'd say you'd get another 900,000 or so.
Dachau (41,500),
Mauthausen-Gusen (100,000),
Janowska (100,000)
Buchenwald (56,000),
Theresienstadt (33,000),
Bergen-Belsen (52,000),
Sachsenhausen (30,000),
Stutthof (85,000),
Neuengamme (60,000),
Ravensbrück (30,000),
Flossenburg (30,000),
Natzweiler-Struthof (22,000),
Ebensee (20,000)
Grossrosen (40,000)
Jasenovac (80,000)
Jadovno (68,000)
Sajmiste (15,000)
Soldau (13,000)
Plaszow (8000)
Klooga (2000)
Vaivara (2500)
Lebrechtsdorf-Potulitz/Potulice (1,291)
Vught/Herzogensbusch (749)
So we're sitting at around 3.8 million.
Then you have Aktion T4, where mentally sick and disabled people were killed in nazi hospitals:
Hartheim (30,000)
Grafeneck (9,839)
Brandenburg (9,772)
Bernburg (8,601)
Sonnenstein (13,720)
Hadamar (10,072)
We're now at around 3.88 million
Remember the holocaust death toll is 11 million civilians, of which 6 million are jews. Are you telling me the remaining 7.1 million were all killed out in the field?