Quick answer
Multiply the pack weight by the protein per 100g, then divide by 100 to find the total grams of protein. Divide the final delivered price by that total. A £24, 1kg bag containing 80g protein per 100g holds 800g of protein, so each gram costs £0.03, or 3p.
The two-line formula
To compare protein powders properly, you need the pack weight, the protein per 100g, and the price you will actually pay. Ignore the manufacturer's scoop size because brands use different servings.
First calculate the protein in the whole pack: pack weight in grams × protein per 100g ÷ 100. Then calculate the cost: final price ÷ total grams of protein. Multiply the result by 100 if you want the answer in pence rather than pounds.
| Step | Calculation | Result |
|---|---|---|
| Total protein | Pack weight × protein per 100g ÷ 100 | Grams of protein in the pack |
| Cost per 1g | Final price ÷ total protein | Price for 1g of protein |
| Cost in pence | Cost in pounds × 100 | Pence per 1g protein |
Worked example: a 1kg bag
Imagine a 1kg bag costing £24 with 80g protein per 100g. Convert 1kg to 1,000g. The bag contains 1,000 × 80 ÷ 100 = 800g of protein.
Now divide £24 by 800. The answer is £0.03 per gram, which is 3p per 1g of protein. This is the number to compare with other products.
Practice comparison: which bag is cheaper?
Bag A costs £22, weighs 1kg, and contains 65g protein per 100g. It holds 650g of protein, so £22 ÷ 650 = 3.38p per gram.
Bag B costs £26, weighs 1kg, and contains 80g protein per 100g. It holds 800g of protein, so £26 ÷ 800 = 3.25p per gram.
Bag A has the lower shelf price, but Bag B provides protein more cheaply. Protein concentration is why comparing the price of the tub alone gives the wrong answer.
| Product | Pack price | Total protein | Cost per 1g protein |
|---|---|---|---|
| Bag A | £22 | 650g | 3.38p |
| Bag B | £26 | 800g | 3.25p |
Use the checkout price, not the advertised price
Apply any valid discount before doing the calculation, then add unavoidable delivery charges. If a £25 bag falls to £20 with a code but costs £3.99 to deliver, use £23.99 unless the delivery charge covers other products in the same order.
Subscription savings, minimum-spend codes and multi-buy offers need the same treatment. Compare the amount you must spend and the amount of protein you actually receive, not the largest percentage printed on the page.
Cheapest Whey Protein
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Common calculation mistakes
Do not divide price by the grams in one scoop. Scoop sizes differ and tell you nothing about the value of the complete pack. Do not treat 80g protein per 100g as 80g in the whole bag. It must be applied to the total weight.
Check that you are using protein per 100g of powder, not protein per serving. Also confirm the nutrition belongs to the selected flavour, because flavoured versions can contain slightly different amounts of protein.
- 1
Convert kilograms to grams before starting: 1kg equals 1,000g.
- 2
Use protein per 100g rather than the serving claim.
- 3
Apply discounts and delivery to obtain the real price.
- 4
Compare products within a category when their purposes differ substantially.
When price per 1g is not the whole decision
Cost per 1g answers a narrow but valuable question: which product supplies protein most cheaply? It does not measure taste, allergens, lactose, third-party sport certification, ingredient preferences or whether a mass gainer and an isolate are meant for the same job.
Use the figure to create a shortlist, then check nutrition per 100g and the qualities that matter to you. The cheapest protein per gram guide explains how UK categories tend to compare, while the live protein comparison performs the calculation automatically against tracked products.
Frequently asked questions
How do I calculate the cost of 1g of protein?+
Calculate total protein as pack weight in grams multiplied by protein per 100g, divided by 100. Divide the final price by that total. Multiply by 100 to express the result in pence.
Should delivery be included?+
Include unavoidable delivery when comparing a single purchase. If one delivery charge covers several items, allocate it sensibly or compare both products before delivery and check the final basket separately.
Is price per 100g of powder the same thing?+
No. Price per 100g accounts for pack size but not protein concentration. Cost per 1g of protein also accounts for how much of the powder is actually protein.
Why not compare protein per scoop?+
Manufacturers choose different scoop and serving sizes. Nutrition per 100g and cost per 1g of protein provide a consistent basis for comparing products.