When adding a food item to the nutrition database, it asks for the number of calories from fat. This is something that should be calculated.
If serving size is in grams, this is an easy calculation. There are 9 calories/g of fat.
I think there should be the option to specify the units for serving size and it should be mandatory to specify in grams.
That is, there should be a field for entering value and another drop down field for selecting the unit (g, cups, ml, oz, pieces or whatever).
The majority of nutrition labels I see always my say serving size is something like "2 pieces" but in parenthesis also state the number of grams right beside it.
This has the added benefit of also allowing me to enter my serving size in g, cups, ml or whatever (as opposed to manually calculating my percentage of the serving size).