concrete.work
United Kingdom

Concrete Block Calculator

Enter the length and height of your wall in metres and the area of any doors or windows. You get the number of standard 440 × 215 mm blocks and the 20kg bags of ready-to-use mortar to lay them.

440 × 215 mm concrete block, 10 mm joints

Measured in feet? Type it like 32' 6" and we convert it.

You need

– blocks

Mortar

Blue Circle Quality Assured Mortar 20 kg, tech data: 0.0135 m³ per bag; 1 m³ (75 bags) lays 2000 blocks 450×225×75, 1500 ×100, 1000 ×150 (10 mm joints)

Link to this calculation Download estimate (PDF)

How to calculate concrete

  1. Measure the wall. Total length of all walls and the height, in metres.
  2. Take out the openings. Subtract the area of doors and windows in m².
  3. Count the blocks. A 440 × 215 mm block with a 10 mm joint covers 450 × 225 mm, so one m² takes 1,000,000 ÷ 101,250 = 9.88 blocks.
  4. Add extra. 5–10% for cuts, corners and breakage.
  5. Mortar. Divide the blocks by the yield per bag for your block thickness: 20 blocks per 20kg bag for 100 mm blocks.

Worked example: a 10 m wall, 2 m high, 100 mm blocks

  1. Area: 10 × 2 = 20 m². Blocks: 20 × 9.88 = 197.5, plus 5% = 208 blocks.
  2. Mortar: 208 ÷ 20 blocks per 20kg bag = 10.4, so 11 bags.
  3. With 150 mm blocks the same wall needs 16 bags (13.3 blocks per bag).

Blocks and mortar for common walls

Wall m² Blocks Mortar 75 mm Mortar 100 mm Mortar 150 mm
3 × 1 m 3.0 32 2 2 3
5 × 1.2 m 6.0 63 3 4 5
6 × 2 m 12.0 125 5 7 10
10 × 1.8 m 18.0 187 8 10 15
10 × 2 m 20.0 208 8 11 16
20 × 2 m 40.0 415 16 21 32
30 × 2.4 m 72.0 747 29 38 57

440 × 215 mm blocks, 10 mm joints, 5% extra. Mortar: 20kg bags of Blue Circle ready-to-use mortar, yields from its data sheet.

Frequently asked questions

How many concrete blocks per square metre?

9.88 standard 440 × 215 mm blocks per m² with 10 mm joints, so about 10 per m² before adding extra for cuts and breakage.

How much mortar do I need for blockwork?

Blue Circle's data sheet says 1 m³ of its ready-to-use mortar (75 bags of 20kg) lays about 2,000 blocks 75 mm thick, 1,500 blocks 100 mm thick or 1,000 blocks 150 mm thick. That is about 27, 20 and 13 blocks per bag.

How many blocks for a 10 m wall 2 m high?

20 m² × 9.88 = 198 blocks, or 208 with 5% extra. Laying 100 mm blocks takes 11 bags of 20kg mortar.

Do UK concrete blocks need their cores filled?

Standard 440 × 215 mm dense concrete blocks are solid, so there are no cores to fill and this calculator doesn't add any. Hollow blocks and reinforced walls follow your engineer's design.

Can I enter the wall in feet?

Yes. Type feet and inches with their marks, like 32' 6" or 6ft, and the calculator converts them to metres.

Does the count include half blocks and corners?

It counts full blocks over the wall area. Corners, ends and cut blocks are covered by the extra percentage; raise it for walls with many corners or openings.