How Many Calories Do Stairs Burn?

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I've decided to start up getting fit again, this time with the help of this website. Last time I went on an exercise binge, it lasted for 6 months, and over that timeframe I lost 15 pounds. I've gained 10 of those pounds back, so now I'm focusing on both exercise *and* diet this time around. Here's my question:

Stair exercises feel like the most effective cardio for me, and generally I can do 20 laps on our home's stairway once or twice a day with no problems. Gets my heart pumping. How many calories am I burning, though? 20 laps is equivalent to 240 up-steps and 240 down-steps. I can do this entire exercise in 8 minutes. I currently weigh 179 pounds and I'm a 5'6" male. The exercise listing in the database doesn't have an option for how many steps.