I have a treadmill at home that I use for short runs when its just too crappy to go out for a 4 or 5 mile run. I dont even look at the distance or the pace, because I know niether is accurate. I just find a pace that feels similar to the effort used to run outside, and I run for time. At the end, I usually find that my mill is short. If I run for about 42 minutes, it usually says I have gone about 4.75 miles, where I would it to be 5.
Just feel it out and run for time.