Concrete Block Calculator
Work out how many concrete blocks, how much mortar and how many bags of mix a wall needs, including waste.
Please note: Material estimates for planning only. Always confirm quantities against your drawings, local building codes and supplier specifications before ordering. Structural work requires a qualified engineer.
What the Concrete Block Calculator does
Block count works exactly like brick count but with far larger units — a standard block covers roughly six times the face area of a brick, so about 10 blocks fill a square metre against 60 bricks.
Formula
Block face with joint = (Length + Joint) × (Height + Joint)Blocks per m² = 1 ÷ Face areaTotal blocks = Net area × Blocks per m² × (1 + Waste %)
Inputs explained
| Input | Unit | Required | Notes |
|---|---|---|---|
| Wall length | number | Yes | Accepts more than 0. |
| Wall length unit | one of 6 options | Yes | — |
| Wall height | number | Yes | Accepts more than 0. |
| Wall height unit | one of 6 options | Yes | — |
| Block size | one of 3 options | Yes | — |
| Block length | mm | In some modes | Accepts 1 or more. Shown Block size is Custom. |
| Block height | mm | In some modes | Accepts 1 or more. Shown Block size is Custom. |
| Mortar joint | mm | Yes | Accepts 0 or more. |
| Total opening area | m² | Optional | Accepts 0 or more. |
| Waste allowance | % | Yes | Extra material for cuts, breakage and offcuts. 5–10% is typical, more for complex layouts. |
| Price per block | selected currency | Optional | Accepts 0 or more. |
| Currency | one of 10 options | Optional | — |
How to use it
- Choose Wall length unit and Wall height unit.
- Enter Wall length, Wall height, Mortar joint and Waste allowance.
- Fill in the remaining inputs the form shows for your choice.
- Optionally add Total opening area and Price per block.
- Select Calculate.
Worked example
A 10 m × 2.4 m wall with UK 440 × 215 mm blocks, 10 mm joints, 5% waste.
- Length
- 10 m
- Height
- 2.4 m
- Block
- UK 440 × 215
- Waste
- 5
Face 450 × 225 mm = 0.10125 m² → 9.88 blocks/m² × 24 m² = 238 blocks, +5% = 249 blocks.
Frequently asked questions
How many blocks per square metre?
Just under 10 for the standard UK 440 × 215 mm block with 10 mm joints. US CMU works out closer to 12.