Why do you want to know? What will you do differently if you find out that you burn 100 calories a day extra, or no calories a day extra, or whatever?
The reason I ask is that your question suggests you're still thinking calories-in/calories-out....that if you can expend a bit more energy standing, you'll lose weight faster. The chances are, you'll just feel hungrier because of the extra calorie burn and eat more without realizing it.
That's not to say I think you should sit down...I do believe we sit far too much!
Zone diet on and off for several years....worked, but too much focus on exact meal composition
Primal since July 2010...skinniest I've ever been and the least stressed about food