Canon 100mm lens help?

-how many feet back would i need to be to capture a full body shot of one person with this lens?I am going to guess a lot more than 15 feet. I can almost get full body shot in my house on a crop sensor with my 50mm and my livingroom is 21 feet wide. I am guessing more like 30 feet. Or more.'

On a full frame sensor 20 feet or so?Well, it depends on if your camera is DX or FX format. I'm going to assume, since you are asking questions on yahoo, that it is a DX. So you would need to stand back a little farther than with an full frame. It also depends on how tall your subject is... lol. I would say that you would need to stand back at least 15ft though. :)