The USDA calculates nutrition based on a 100 gram portion size.
Your inventory ingredients need to have a Pack Size or at least one Conversion that is a weight.
It does NOT have to be in grams because reciProfity internally will calculate the grams based on the weight in Conversions.
For example, if you use an ingredient by the cup in a recipe, cup is not a weight, it's a volume. The USDA need a weight.
Use Conversion for the volume to weight conversion.
reciProfity will look at Conversions and see the cup to weight conversion and then calculate nutrition based on that weight.