This is a tough question because it varies with the food. For example, the wheat thins next to me say a serving size is 16 pieces but I rarely eat more than 10 at a time. So _my_ serving size is 10. As for something like fried rice you need to decide how much you want to eat and then compare that to what a known restaurant publishes to get an idea of nutrition for that food. PFChangs is a reasonable place to use for comparison. Look at their nutrition info (MyFitnessPal lists them, I'm not sure of fitbit) and see what they say is a serving. Let's say they use 10oz as a serving. Personally, _I_ think their servings are HUGE so when I use their data I cut it into thirds or half. If I am only eating fried rice I'd say _my_ serving is 2/3 of PFChang's but if I'm having anything else with it I'd say 1/2. You can also look at calorieking.com to get an idea of serving sizes for basic things like fruit, bread, vegs, meat, etc. This is pretty well standardized by dieticians and the like.
