It depends how much you weigh and how fast you walk really. For a woman of average height who walked fairly briskly for half an hour I would say she would burn around 100 calories. If you go to google and type in 'calories burned calculator' you'll be able to find that out easily.
Thanks. I'm average height (5 foot 3), 13, and about 112 pounds. If that helps you.
thanks to everyone who answered. :)
it depends on your pace.. try a pedometer
maybe 500, rough guesstimate