Hello, there have been several threads that look at the numbers, and discuss the sources. The first thing to be clear on is that the 6 million refers to Jewish deaths at the hands of the German military during WWII by all means, not only in the gas chambers. So that includes deaths by shooting, starvation in work camps, etc. Take a look through these; most of these posts have been archived, so if you have follow-up questions for any of these users, please feel welcome to ask them here: just tag their username to notify them.

• Who was the person that determined the statistic that 6 million jews were killed in the Holocaust? - /u/angelsil cites the origin of the estimates as Wilheml Hoettl during the Nuremberg trials

• Have death estimates on the Holocaust remained the same in academic circles for the past seventy years? Or has there been major changes in the numbers? - /u/mystical-me introduced a couple of later estimates

• How many Jews actually died in the Holocaust? - /u/Sid_Burn provides a quick survey of estimates from various analysts, and breaks down Jewish deaths by country

• Is there any majoritary position on the jewish total casualties during second world war? - /u/estherke breaks down Jewish deaths by method

• 6 million victims of the holocaust. HUGE number - a recent discussion thread. Some comment describe specific incidents, more citations of numbers and sources