Calculating calories burned during activity

Fist post ever on any forum, so please be kind because I'm a bit shy :) I'm wondering what unit of measure is used to track activity. I assume it is minutes not hours and does the program take into account your size ? for example; I am a 285 pound 53 year old woman. I spent the better part of the day doing house work: vacuuming, dusting, light yard work, laundry (which involved 3 flights of stairs up n down each load). when I entered 5 hours (300 minutes) it came in just under 1000 calories burned. Is this possible ?