Um, depends on the yoga, let's say 200-300 on average. You'd be much better off if you took a more comprehensive program like this one: http://goo.gl/RrgRls Yoga alone is insufficient for long-term weight loss.
Many will ask the difference of yoga and regular exercise as to how many calories does yoga burn, and interesting enough on an average it can burn about 200 calories per hour. Again this depends on which type of yoga you practice, how intense your yoga is as well as how you challenge yourself in your yoga workout. For more information on this query you can visit this site http://www.elysiumyoga.com/cals.html.