Concrete Block Calculator
How many concrete blocks a wall needs, plus the mortar, and the cost — from the wall size and the block you are using.
How many blocks to order for the wall.
How the concrete block calculator works
Blocks are counted by area: wall area divided by the face area of one block including its mortar joint. A standard 390 × 190 block with a 10 mm joint covers 0.08 m², so a square metre takes 12.5 blocks.
Mortar is the joint volume — roughly 0.02 m³ per square metre of 10 mm joints in blockwork, which is about one 20 kg bag of mix per square metre. Both figures here include a waste allowance you can set.
Formula: blocks = wall area / (block length × height, joints included)
Worked examples
| Inputs | Blocks needed | Note |
|---|---|---|
| 10 × 2.4 m wall, 390 × 190 blocks | 315 | 315 blocks |
| With a 2 m² door | 289 | about 26 blocks fewer |
| UK 440 × 215 blocks | 249 | fewer, larger blocks |
FAQFrequently asked questions
How many blocks per square metre?
With a standard 390 × 190 block and a 10 mm joint, 12.5. UK 440 × 215 blocks give about 10 per square metre.
How much mortar do I need?
Roughly 0.02 m³ per square metre of blockwork — about two 20 kg bags of mix per square metre, though the exact figure depends on joint thickness and how much you waste.
Should I deduct windows and doors?
Yes for anything over about a square metre. Small openings are usually left in as a buffer against cutting waste.
How much waste should I allow?
5% for a simple rectangular wall, 10% or more where there is a lot of cutting around openings and corners.
Do I need to allow for the bond?
Half-bond blockwork produces a half block at the end of alternate courses. That is what the waste allowance covers.
Where these figures come from
- The Engineering ToolBox — material densities, coverage and unit data — bulk densities, concrete at 2,400 kg/m³, board and sheet sizes
- Brick Development Association — brick sizes and quantities — 215 × 102.5 × 65 mm, 60 bricks per m²
- UK Government — Approved Documents (Building Regulations) — Building Regulations guidance
Last checked: September 2026. Coverage rates and material sizes are typical manufacturer figures — check the product you buy.