I personally weigh it cooked since that's the way I'm eating it. Some weight is usually lost in cooking but Fitday gives calories for both raw and cooked for most meats, so you can use it either way.
I'm the opposite. I weight it raw. It's pretty rare that I eat meat by itself, it is almost always going into a casserole, stew, soup, pasta or rice dish, or some other recipe, so weighing it afterwards would be impossible. And, most recipes state the amount of raw meat required, not cooked meat. About the only meat I weigh cooked is lunch meat.
I weigh it raw because I don't cook it plain, and weighing it when it's dripping with sauce or cheese or marinade or whatever can get quite messy The back of my chicken package has the nutritional info for both cooked and raw (I think it says something like 2.4oz raw, 2oz cooked is a serving). I guess the answer is--it depends on the nutritional info you're trying to use! As previously menitoned, Fitday and most other sites include info for both raw or cooked amounts.
I have 2 different brands of chicken breast, 1 says 100 calories per 4 oz the other says 140 calories per fillet. When I cooked it last night I weighed it and it was just under 4 oz cooked, the package doesn't say raw or cooked.
If the package doesn't say raw or cooked, then the calories and weight are for the raw amount. So for the 100-calories-per-4-oz chicken, it is 100 calories per 4 oz of raw chicken, which will be 100 calories for something less than 4 oz of cooked chicken (since 4 oz of raw chicken will weigh slightly less when cooked). With chicken, it is mainly just water that is cooking out and reducing the weight, so you aren't really losing any calories during the cooking process (this might be different for very fatty meats, however, if you are really good about draining off the fat). In the US, food manufactures are required to give the nutritional data for the food as it is packaged and can optionally include nutrition for it as prepared. The fillets should be 140 calories raw or cooked, but of course, they'll be slightly smaller once they are cooked.
Also, bear in mind that isn't an exact science, it's all just an estimate anyway. There isn't that much weight or caloric difference between raw or cooked meat, so it's not worth losing sleep over it.
Food weights
The back of my chicken package has the nutritional info for both cooked and raw (I think it says something like 2.4oz raw, 2oz cooked is a serving). I guess the answer is--it depends on the nutritional info you're trying to use! As previously menitoned, Fitday and most other sites include info for both raw or cooked amounts.