It’s estimated about 8M people live in the territory controlled by ISIS, and that ISIS has killed something like 170,000 people.
That’s somewhere around 2% at this point. Way, way below the percentage killed by the Khmer Rouge. The Rwanda genocide killed around 800,000 people, from a population about the same size as that of the Islamic State.
The 170,000 number killed by ISIS is probably way too high.