Why price per serving can mislead
Serving sizes vary between brands. One product might use a 25g serving while another uses 35g, which makes headline cost per serving hard to compare fairly.
Cost per gram of protein is stricter because it combines price, pack size and protein density. This is the metric to use when your main goal is value.
How to calculate protein value
Start with the total tub price, divide it by the pack weight, then factor in the protein percentage. A product that is 80g protein per 100g gives 800g of protein in a 1kg bag.
If that 1kg bag costs £20, the protein cost is 2.5p per gram of protein. This lets you compare whey, isolate and vegan protein on the same basis.
What usually wins
Large whey concentrate packs often produce the cheapest protein per gram, especially when a retailer runs a strong discount code.
Isolate can still be worth buying when you care about lower carbs or calories, but it has to be compared against your actual nutrition goal, not only price.