Estimates vary and are continously raised as more Iraqis come forward. Some estimates exceed 6 million civilians during his official reign depending on if one counts the WMDs used on the Kurds and the destruction of the Shia in Basera and the sounthern wetlands areas, but even these don't take into account his hienous actions before becomming dictator. A reference point for estimating how many people died would be that US Troops found %50 of Iraqis knew of, or were related to, someone Saddam killed throughout his life.
But we are still digging up mass graves and trying to ID bodies.... He didn't do what the Serbs did and use a saugsage factory to grind the poor victims up, which makes counting bodies easier (I don't mean that to sound callous, but after seeing that site in Brcko, Serbia I was sick beyond belief) but he did things equally as cruel. Things his paternal uncle, a NAZI ally in WWII would have loved just as much. His son, Uday, used a printing press or some other type of double roller press to crush victims feet first, and then there was the electic shock rooms filled partially with water, and the underground prisons were he kept children as leverage against their families (UK found them), and the list goes on, and on, and on.
So trying to do the forensic analysis is difficult, as is getting an accurate count of bodies.