Calculate protein grams per dollar from a whole pack
Use net weight, declared protein, and the actual pack price to calculate a transparent price-based ratio.
Protein grams per dollar is a narrow purchasing ratio: estimated protein in the purchased food divided by its price. It can help explain one cost difference, but it is not a score for protein quality or the overall value of a diet.
Use a declared nutrient quantity with a clear weight basis, such as the per-100-g declaration described in the EU food information regulation. The prices and product values below are hypothetical.
Calculate protein in the whole pack first
Pack A contains 300 g of food and lists 18 g protein per 100 g. Its estimated package protein is 18 × 300 ÷ 100 = 54 g. If it costs $4.50, the ratio is 54 ÷ 4.50 = 12 g protein per dollar.
Pack B contains 500 g and lists 12 g protein per 100 g. That gives 60 g protein per pack. At $6.00, its ratio is 10 g per dollar. B contains more total protein, while A provides more calculated protein for each dollar spent.
Check with the inverse ratio
The inverse calculation is price divided by estimated protein. A costs approximately $0.0833 per gram of protein; B costs $0.10. Expressing this as cost per 10 g protein gives approximately $0.83 for A and $1.00 for B.
Keep rounding until the end. If you round A's cost to $0.08 too early and multiply it repeatedly, the cumulative estimate moves away from the original pack price. Retain the full calculation internally and show an appropriately rounded result.
Choose a denominator you can actually use
If some of the purchased material is discarded, the full pack's estimated protein may not all be consumed. Draining, bones, shells, or leftovers require a clearly defined edible-quantity basis. Do not assume all protein remains after a preparation step that discards food or liquid.
For real price checks, record the currency, date, pack size, and conditions of any offer. A multi-buy discount may require spending more money or purchasing more food than a single pack comparison suggests.
Keep the conclusion literal: “12 estimated grams of protein per dollar under these inputs.” The ratio cannot establish amino-acid composition, medical suitability, allergen safety, or the appropriate portion for a person. Those questions need information beyond price and a protein total.