>>17759284 (OP)I reckon around 2.5-4.5 million. It's indisputable that many many Jews were killed, it's just being ignorant to say otherwise but the amount of logistics, manpower etc. to carry out >5 million is unrealistic.
A commonly cited number is 1.3 million from the Einsatzgruppen which is totally ridiculous. For a group of ~3,000 people to coordinate cleansing of villages (which took a number of weeks to coordinate with local collaborators) and to carry them out all between June 41 to around the start of 44 (2.5 years) when the Germans had been pushed out of Russia, White-Russia, and Ukraine is just not possible.
Gas chambers were almost certainly used to kill people although probably exaggerated and were mainly for delousing (even Irving acknowledges uses of chambers to kill people). Most died probably of Typhus/ hunger/ other diseases.
People saying less than 2-3 mil are either trolling or not intellectually rigourous