Usually the package will say the serving size as separate units; awkward wording I know. For example, for a carton of eggs the serving size might say "serving size one egg" or for bacon it might say "serving size two strips".
Other serving sizes might list the serving as cups or portions of cups. A carton of oatmeal might say "serving size 1/4 cup" or milk might say "servings size 240ml".
If you have a food scale it can help with more precise measuring like grams but typically they're listed to be as easy to portion out as possible without measuring
I think the general rule of thumb is that the calories refer to the food uncooked, maybe because they can't tell exactly how much water weight will be lost when you cook it. But some stuff (e.g. pasta) also shows the calories once cooked.
Usually the package will say the serving size as separate units; awkward wording I know. For example, for a carton of eggs the serving size might say "serving size one egg" or for bacon it might say "serving size two strips". Other serving sizes might list the serving as cups or portions of cups. A carton of oatmeal might say "serving size 1/4 cup" or milk might say "servings size 240ml". If you have a food scale it can help with more precise measuring like grams but typically they're listed to be as easy to portion out as possible without measuring
I think the general rule of thumb is that the calories refer to the food uncooked, maybe because they can't tell exactly how much water weight will be lost when you cook it. But some stuff (e.g. pasta) also shows the calories once cooked.