How to Calculate Protein Cost Per Serving: A Practical Step-by-Step Guide

UK protein powder sells in confusingly different formats. Bag sizes range from 250g sample tubs to 5kg bulk bags. Scoop sizes range from 25g to 40g. Protein content ranges from 55g to 92g per 100g of powder. A direct comparison of two tub prices means little because none of those variables stay constant.

Marketing makes it worse. A 1kg tub priced at £29.99 next to a 2.5kg bag priced at £52 looks like the smaller tub costs less. The 2.5kg bag actually runs roughly 30 percent cheaper per gram of powder. Add a difference in protein density and the gap widens further.

The maths itself is simple. The reason it matters is that almost nobody runs it, which is exactly why so many people end up overpaying.

Cost per serving: (Price divided by bag size in grams) multiplied by scoop size in grams equals cost per serving.

Use this when comparing two products with the same protein content per 100g and the same scoop size, for example two whey concentrates at 75g of protein per 100g with a 30g scoop.

Cost per 25g of protein: (Price divided by (bag size in grams multiplied by protein per 100g, divided by 100)) multiplied by 25 equals cost per 25g of protein.

This metric handles every variable at once: bag size, scoop size, and protein density. It is the only fair way to compare a 1kg tub of whey isolate at 88g per 100g against a 2.5kg bag of whey concentrate at 72g per 100g. Use this formula across every product type and every UK retailer.

Three real UK whey products at typical 2026 sale prices, run through both formulas.

1. 1

   MyProtein Impact Whey, 2.5kg, £30 on Impact Week, 82g protein per 100g, 25g scoop. Cost per serving: (30 divided by 2500) multiplied by 25 equals £0.30 per scoop. Total protein in the bag: 2500 multiplied by 82, divided by 100, equals 2050g. Cost per 25g protein: (30 divided by 2050) multiplied by 25 equals £0.37.

2. 2

   Bulk Pure Whey, 2.5kg, £42 standard sale, 80g protein per 100g, 30g scoop. Cost per serving: (42 divided by 2500) multiplied by 30 equals £0.50 per scoop. Total protein in the bag: 2500 multiplied by 80, divided by 100, equals 2000g. Cost per 25g protein: (42 divided by 2000) multiplied by 25 equals £0.53.

3. 3

   Optimum Nutrition Gold Standard, 2.27kg, £55 on sale, 79g protein per 100g, 30g scoop. Cost per serving: (55 divided by 2270) multiplied by 30 equals £0.73 per scoop. Total protein in the bag: 2270 multiplied by 79, divided by 100, equals 1793g. Cost per 25g protein: (55 divided by 1793) multiplied by 25 equals £0.77.

Ranked on cost per 25g of protein: MyProtein at £0.37, Bulk at £0.53, Gold Standard at £0.77. The premium protein costs more than twice as much per 25g of actual protein as the cheap one, yet the protein content gap between them measures only a few grams per 100g. The price gap runs much larger than the quality gap.

Five recurring errors show up when comparing UK protein powder value.

1. 1

   Comparing tub prices instead of cost per 25g of protein. A 1kg tub at £30 looks cheaper than a 2.5kg tub at £55 until the maths shows the 2.5kg tub runs 27 percent cheaper per gram of powder.

2. 2

   Ignoring protein percentage. A budget protein at 60g protein per 100g costs more per 25g of protein than a slightly pricier one at 80g per 100g, even when the cheap tub looks cheaper. Always read the back label.

3. 3

   Comparing pre-sale RRP rather than actual sale price. MyProtein's RRP is fictional. Use the price you actually pay. Bulk and the Protein Works follow the same pattern.

4. 4

   Forgetting shipping. A £25 bag with £6 shipping is really a £31 bag. Direct to consumer brands often offer free shipping above £40 to £55, so combining purchases drops the per kilogram price.

5. 5

   Using cost per scoop alone. A 25g scoop and a 40g scoop are not comparable. Cost per 25g of protein normalises this difference.

The maths above takes about 60 seconds per product to run by hand. ProteinDeals exists specifically so you do not have to. Every product in the database, 1,958 UK protein powders across 85+ retailers as of April 2026, gets normalised to cost per 25g of protein automatically and updated weekly.

The main comparison page sorts by cost per 25g of protein by default. The cheapest protein per 25g page surfaces only the lowest cost options across all categories. The whey concentrate, whey isolate, vegan, and casein category pages each rank within their own type.

Understanding the formulas still pays off. Knowing why one product costs less per 25g of protein than another helps you spot fake bargains (a £20 tub at 50g protein per 100g is not one) and helps you judge whether a sale genuinely counts as a deal or just carries a clever name.

Two adjustments are worth making after the basic formula.

1. 1

   Apply the actual discount code. MyProtein and the Protein Works both run frequent multi tier codes (40 percent off, 50 percent off, 60 percent off on Impact Week or seasonal promos). Your cost per 25g of protein is the post code price, not the sticker price. Sign up to brand emails to see codes early.

2. 2

   Step up bag size where you can. A 2.5kg bag typically runs 15 to 25 percent cheaper per kilogram than a 1kg bag of the same product. A 5kg bag is usually another 5 to 10 percent cheaper per kilogram than 2.5kg. Scale up once you have committed to a brand and flavour.

3. 3

   Check whether the same product is cheaper at Amazon UK. For brands like Applied Nutrition, Optimum Nutrition, Mutant Whey, and Warrior, Amazon UK sometimes runs meaningfully cheaper than the brand's own site. For Bulk and MyProtein, direct almost always wins. ProteinDeals tracks both and shows the cheapest UK retailer per product on the full comparison page.

Cost per serving is the price of one scoop of powder, calculated as price divided by bag size, multiplied by scoop size. It works well when comparing two products with similar protein densities and scoop sizes. For different brands and formats, cost per 25g of protein gives a more accurate picture.

Use cost per 25g of protein, which normalises bag size, scoop size, and protein percentage into one metric. Apply actual sale prices and discount codes, not RRP. ProteinDeals calculates this automatically for every UK product on the comparison page.

In 2026, anything under £0.40 per 25g of protein counts as excellent value. £0.40 to £0.55 is reasonable. Above £0.70 you are paying a premium for brand or certification. The cheapest UK options live on the cheapest protein per 25g list.

Scoop size determines how much protein you actually consume per serving. A 25g scoop at 80g protein per 100g delivers 20g of protein, while a 30g scoop at 70g protein per 100g delivers 21g. The cost per 25g of protein metric controls for this and gives a directly comparable number.

Almost always, yes. UK direct to consumer brands consistently price 2.5kg and 5kg bags 15 to 25 percent cheaper per 100g of powder than 1kg tubs of the same product. The exception is short term sales where a smaller bag gets discounted more aggressively. Check both formats before buying.