Cement Calculator: Cement, Sand & Aggregate

Mixing your own concrete or mortar? Get the cement bags, sand, gravel and water for 1:2:3, 1:2:4, 1:3 or 1:4 mixes, from dimensions or a volume.

Mixing your own concrete or mortar means buying cement, sand and gravel separately and combining them by volume ratio, such as 1:2:3 (one part cement, two parts sand, three parts gravel). Because the dry materials pack together when water is added, a cubic metre of finished concrete needs about 1.54 m³ of dry materials. For 1 m³ of 1:2:4 concrete that's 1.54 ÷ 7 = 0.22 m³ of cement, about 317 kg or 13 × 25 kg bags, plus 0.44 m³ of sand and 0.88 m³ of gravel. This calculator does that for common concrete mixes, UK cement-and-ballast mixes, and mortar and screed mixes from 1:3 to 1:6. Enter the dimensions or the volume you need and it gives the cement bags, sand, aggregate and water, with the working shown.

Units
Bag sizes
Mixing
Enter
Area
ft
ft
in
Feet and inches work too: type 12'6 or 12.5.
%
Cement
9 bags

94 lb bag (1 ft³) · 808 lb

Sand
0.9 tons

0.67 yd³ · 1,795 lb

Gravel / aggregate
1.26 tons

1 yd³ · 2,524 lb

Water
48.38 gal

183 litres

How it was worked out
  1. Area: 10 ft × 10 ft = 100 ft²; × 4 in (0.333 ft) deep = 33.33 ft³
  2. 33.33 ft³ ÷ 27 = 1.23 yd³
  3. Plus 5% extra = 1.3 yd³ of concrete
  4. Dry materials bulk up when wet, so multiply by 1.54: 35 ft³ × 1.54 = 53.9 ft³ of dry materials
  5. 1 : 2 : 3 is 6 parts, so 1 part = 8.98 ft³
  6. Cement: 8.98 ft³ × 1,440 kg/m³ = 366 kg (808 lb) ÷ 94 lb = 9 bags
  7. Sand: 2 parts = 17.97 ft³
  8. Gravel / aggregate: 3 parts = 26.95 ft³
  9. Water at a water–cement ratio of 0.5: 183 litres (48.38 US gallons)

Assumes loose densities of 1,440 kg/m³ for cement, 1,600 for sand, 1,500 for aggregate and 1,650 for ballast, and a dry-volume factor of 1.54 for concrete and 1.33 for mortar. Damp sand bulks up, so measure by the bucket or shovel and adjust water as you go.

Common use cases

  • Order cement, sand and gravel for a site-mixed slab or footing
  • Work out sand and cement for bricklaying mortar, render or a floor screed
  • Mix concrete from cement and all-in ballast (UK)
  • Check how much cement a mix ratio really uses

How to use

  1. Choose concrete or mortar and screed, and your units and bag sizes.
  2. Pick a mix ratio. Each option says what it's typically used for.
  3. Enter the dimensions of the pour, or switch to Volume and type the amount you need.
  4. Read the cement bags, sand, aggregate and water. Adjust the water–cement ratio if your mix needs it.

FAQ

How much cement is in a cubic metre of concrete?

It depends on the mix. Using the 1.54 dry-volume factor and cement at 1,440 kg/m³: about 317 kg for 1:2:4, 370 kg for 1:2:3 and 403 kg for 1:1.5:3. In 25 kg bags that's roughly 13, 15 and 17 bags.

How many bags of cement for a cubic yard?

A cubic yard of 1:2:3 concrete takes about 283 kg (623 lb) of cement, or about 7 × 94 lb bags, using the same assumptions.

What is the 1.54 factor?

Dry cement, sand and gravel have air gaps between the particles. When they're mixed with water, the sand fills the gaps in the gravel and the cement paste fills the rest, so the finished concrete takes up about 1 ÷ 1.54 of the dry volume. For mortar, which has no gravel, a factor of about 1.33 is used.

What mortar mix should I use?

General brick and blockwork is often laid with 1:4 to 1:5 cement to building sand, with weaker mixes such as 1:6 for internal walls and stronger ones such as 1:3 for work below ground. Floor screeds are commonly 1:3 to 1:5 with sharp sand. Follow your plans or the brick or block maker's guidance where it applies.

How much water does concrete need?

A water–cement ratio of about 0.5 by weight is a common starting point: half a litre of water for every kilogram of cement. Less water makes stronger concrete but it's harder to work. Sand is often damp, so add water gradually.

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