Historians cannot give a single exact number, but millions of people were imprisoned and murdered in Nazi concentration camps and related camps during 1933–1945.

Key numbers (what historians estimate)

  • In the core Nazi concentration camp system , about 1.65 million people were formally registered as prisoners.
  • Of these registered prisoners, roughly 0.8–1.1 million died in the camps (from starvation, disease, executions, overwork, and other abuse).
  • When you add Jews who were killed on arrival at killing centers like Auschwitz (without ever being registered), total deaths in the concentration‑camp system are estimated at about 1.9–2.0 million or slightly more.
  • If you zoom out to the entire network of Nazi camps and ghettos (concentration camps, slave‑labor camps, ghettos, POW camps, brothels, etc.), researchers estimate there were around 42,500 separate sites, and “millions of people” were imprisoned, abused, and murdered there.
  • Some historians, looking at all types of Nazi camps and ghettos together, estimate that as many as 15–20 million people may have died in this broader system, though this range is debated and depends on which sites and victim groups are counted.

Why the numbers are hard to pin down

  • The Nazis destroyed records and bodies, especially near the end of the war, to hide evidence.
  • Different studies count different types of sites: some look only at classic concentration camps, others include forced‑labor camps, transit camps, ghettos, and POW camps.
  • Many victims, especially Jews murdered on arrival at killing centers, were never registered by name, which makes exact counting impossible.

A broader picture

  • The Holocaust as a whole killed about six million Jews through camps, ghettos, mass shootings, and killing centers; about 2.7 million of those were murdered in five main killing centers alone (Chełmno, Bełzec, SobibĂłr, Treblinka, Auschwitz‑Birkenau).
  • Beyond Jewish victims, millions of non‑Jewish prisoners (Poles, Soviet POWs, Roma, disabled people, political prisoners, LGBTQ+ people, and others) were also incarcerated and killed in the wider camp network.

One way to summarize

If your question is strictly “How many people were in concentration camps?” during the Nazi period, a careful, historically grounded summary is:

  • Around 1.65 million people are known to have been registered in the main concentration camp system, with about 1–1.1 million of those dying in the camps.
  • Including unregistered victims murdered on arrival and the broader system of camps and ghettos, the total number of people imprisoned reaches many millions, and total deaths may reach into the mid‑tens of millions, though exact figures remain uncertain and debated.

Information gathered from public forums or data available on the internet and portrayed here.