How long it takes to burn 100 calories depends on the type of activity. Every activity, from breathing to step aerobics, burns calories. Everyday chores, such as sweeping and mopping, burn 100 calories in about 20 minutes of constant activity.
Gardening can burn 100 calories in as little as 15 minutes. Walking around the block burns 100 calories in 20 minutes at a 3-mph pace. More aerobic activities obviously burn 100 calories in a much shorter amount of time. Zumba burns 100 calories in 11 minutes, while running on stairs can shed 100 calories in as little as six minutes.