Best Value Protein Tub Size: 1kg vs 2kg vs 5kg per 25g of Protein (UK)

Every figure below uses the exact one-off price retailers were charging on 22 to 24 October 2026, without subscriptions or codes, across seven UK whey powders.

How much does protein cost per 25g in each pack size?

Every powder we priced is cheaper per 25g of protein in a bigger bag, but the size of the saving varies a lot. Optimum Nutrition Gold Standard and NutriSport 90+ cut about a quarter off the cost per 25g of protein in their biggest tub, while Protein Works Whey Protein 360 Black and Myprotein Impact Whey save under 2% between their two largest sizes.

Each cell shows the pack, its one-off price and its cost per 25g of protein. Protein Works prices are from its own product pages; its OnTap subscription is about 15% cheaper in every size.

Myprotein pack weights vary by flavour, so we use its core flavours. Protein Works 360 Black and Gold, Bulk Basic Whey and NutriSport 90+ are blends that include soy protein.

Are larger protein tubs actually cheaper per serving?

Yes, but most of the saving comes from the first step up, not the last. Moving from the smallest bag to about 1kg cuts the cost per 25g of protein by 7% to 18% at the brands we priced: Bulk Pure Whey drops 18%, from £1.41 to £1.16, and Protein Works Whey Protein 360 Black 7%, from 81p to 75p. Above 2kg, the next step saves under 4% at three of the six powders that offer one, though NutriSport 90+ and Optimum Nutrition Gold Standard save 24% and 13%.

The same is true per serving, because a serving is just a fixed amount of powder. What changes between brands is how much protein that serving holds, which is why we compare on 25g of protein rather than on the brand's own scoop.

How do 2kg protein tubs compare with 1kg bags on price?

A 2kg to 2.5kg bag is usually 4% to 13% cheaper per 25g of protein than the same powder in about 1kg. Bulk Pure Whey on Amazon UK costs £1.16 per 25g of protein in the 1kg bag and £1.10 in the 2.5kg bag, 5% less. Protein Works Whey Protein 360 Gold drops 8%, from 88p in the 1.2kg bag to 81p in the 2.4kg, and Optimum Nutrition Gold Standard 13%, from £1.63 in its 900g tub to £1.42 in the 2.27kg.

In money, the gap is modest at three shakes a week. Over a year of 156 shakes, Bulk Pure Whey in the 2.5kg bag saves about £10 over buying 1kg bags, and Optimum Nutrition Gold Standard in the 2.27kg tub saves about £33 over the 900g tub.

Which protein powders are worth buying in 5kg bags?

NutriSport 90+ is the clearest case for a 5kg bag: 42p per 25g of protein against 55p in the 2.5kg, a 24% saving that makes it the cheapest milk-based powder in our monthly ranking. Optimum Nutrition Gold Standard is the other: its 4.54kg tub costs £1.23 per 25g of protein against £1.42 in the 2.27kg, 13% less. For Bulk Pure Whey, Protein Works Whey Protein 360 Black and Myprotein Impact Whey, the biggest bag saves under 4% over the next size down, so it is only worth it if you use protein daily.

Biggest saving in a 5kg bag

NutriSport 90+ Protein

2.5kg bag

The one powder we priced where the 5kg bag is clearly worth it, if you will use 5kg.

Buy 90+ Protein →See the price on Amazon

Biggest saving in a 5kg bag

NutriSport 90+ Protein

2.5kg bag

Pros

• + 42p per 25g of protein in the 5kg bag on Amazon UK
• + 24% cheaper per 25g of protein than its 2.5kg bag
• + 76g of protein per 100g

Cons

• – A blend of whey, casein, soy and rice protein, not pure whey
• – The 5kg price is for one flavour

Pros

• 42p per 25g of protein in the 5kg bag on Amazon UK
• 24% cheaper per 25g of protein than its 2.5kg bag
• 76g of protein per 100g

Cons

• A blend of whey, casein, soy and rice protein, not pure whey
• The 5kg price is for one flavour

Buy 90+ Protein →See the price on Amazon

●Nutrition per scoop · 45.6g protein in 60g▼

Protein makes up 76%

of this 60g scoop · 214 kcal total

45.6g

Protein45.6g

Carbs6g

Fat0.8g

Other7.6g

Who offers the best value on large bags of protein powder?

NutriSport 90+ has the best value large bag we found, at 42p per 25g of protein in 5kg on Amazon UK. From a brand's own website, Protein Works Whey Protein 360 Black is cheapest at 71p in the 4.8kg bag, or about 63p with code WW12. If you want 100% whey concentrate rather than a blend, Bulk Pure Whey is the cheapest large bag at £1.06 per 25g of protein in 5kg.

For the cheapest powders in every size, not just the big bags, see this month's cheapest protein powder per 25g ranking.

What's the best protein powder pack size for three shakes a week?

For three shakes a week, a 2kg to 2.5kg bag is the best size for most people. Three shakes of 25g of protein use about 100g to 130g of powder a week, so a 2.5kg bag of Bulk Pure Whey lasts about 24 weeks, nearly six months, and gets most of the per-25g saving. A 5kg bag would last close to a year, which ties up more money for a saving of a few pounds.

We size each shake at 25g of protein, inside the 20g to 40g per serving the International Society of Sports Nutrition suggests (ISSN position stand on protein and exercise, 2017).

Before you buy a big bag, check that the best-before date on the pack covers how long you will take to finish it. If you have one shake a day instead, multiply by about 2.3: a 2.5kg bag lasts about ten weeks and a 5kg bag about five months, which is where the biggest bags start to make sense. Our guide to how much protein powder to take a day helps you work out your own number.

When is a smaller bag the better buy?

A smaller bag is the better buy when you are trying a new flavour or brand, when you train only now and then, or when a big bag would outlast its best-before date. The extra cost is small next to throwing away half a bag you do not like: a 1.2kg bag of Protein Works Whey Protein 360 Gold costs 13p more per 25g of protein than the 4.8kg bag, or about £4 over 32 shakes.

• Trying a flavour: buy around 1kg, not the smallest bag, which carries the biggest premium.
• Training a few times a week: 2kg to 2.5kg.
• One shake a day or more: 4.5kg to 5kg, if the powder's biggest bag gives a real saving.

WheyWise compares every pack size on cost per 25g of protein on the whey comparison, and the cheap vs expensive protein guide covers whether a dearer powder is worth it in the first place.

Frequently asked questions