What is the standard bag size for cement in the UK?

Standard UK cement bags are 25kg. This applies to most brands including Blue Circle, Hanson, and Cemex. Some specialist products come in different sizes, but 25kg is the industry standard available at all builder's merchants, Screwfix, B&Q, and Wickes.

How heavy is a bulk bag of sand or aggregate?

A standard bulk bag (also called a jumbo bag or ton bag) of sand or aggregate typically weighs around 850kg, not a full tonne as many people assume. This is because the bags are filled by volume, and the weight varies by material density. Always check with your supplier for exact weights.

How many 25kg bags make a tonne?

A tonne (1,000 kg) requires 40 × 25kg bags. This is useful to know when comparing the price of buying individual bags versus ordering bulk. Bulk delivery is almost always cheaper for quantities above 20-30 bags.

Should I always round up the number of bags?

Yes, always round up to the next whole bag. You cannot buy partial bags, and it is far better to have a small amount left over than to run short mid-job. The remainder shown in the calculator tells you how much spare material you will have.

What size bags does Postcrete come in?

Postcrete (post-mix concrete) comes in 20kg bags, not 25kg like standard cement. Each 20kg bag of Postcrete typically sets one fence post (in a hole approximately 300mm × 300mm × 600mm deep). For most fence posts, one bag per post is sufficient.

TradeCalcs

Kg to Bags Converter — How Many Bags Do I Need?

Convert a total weight in kilograms to the number of bags you need to buy. Covers cement, plaster, sand, aggregate, postcrete, and more with standard UK bag sizes.

Total Weight Needed

How many kg of material do you need in total?

Material Type

Price Per Bag (optional)

Enter your supplier price for a cost estimate

How We Calculate This

This converter divides your total weight requirement by the selected bag size, then rounds up to the nearest whole bag. You cannot buy partial bags, so we always round up to ensure you have enough material.

The formula

Bags needed = ROUNDUP(Total weight ÷ Bag size)

For example, if you need 120kg of cement in 25kg bags: 120 ÷ 25 = 4.8, rounded up = 5 bags. You'll have 5kg spare (5 × 25 = 125kg total purchased).

Standard UK bag sizes

Cement: 25kg bags
Plaster: 25kg bags
Sand / Aggregate: 25kg bags or 850kg bulk bags
Postcrete: 20kg bags
Self-Levelling Compound: 25kg bags
Tile Adhesive: 20kg bags
Grout: 5kg bags

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Last updated: February 2026

All calculations are estimates. Verify with your supplier.