How do you calculate net carbs in food?

I have changed my eating habbits to low carb, to loose weight. It has been VERY easy for me and has many health benefits I wasn't aware of. I just struggle with how to calculate "net" carbs instead of all carbs.

Net carbs are total carbs in grams minus fiber in grams.

http://www.ehow.com/how_4744078_calculate-net-carbs-food.html