About the Concrete Block Calculator
Blocks needed for a wall with mortar, waste allowance and cost, for any block size.
Also known as: cinder block calculator, how many blocks, concrete masonry units, cmu calculator, breeze block.
How to use this calculator
- Enter wall length, wall height, block size, mortar joint and the other fields.
- The result updates instantly as you type — press Calculate (or Enter) at any time.
- Review the breakdown shown under the main result.
- Use Copy result or Share to save the answer or send a link with your inputs.
Formula
blocks = net wall area ÷ block face area including joints
Worked example
Using the values pre-filled in the calculator above:
- Wall length = 12 m
- Wall height = 2.4 m
- Block size: UK 440 × 215 mm
- Mortar joint = 10 mm
- Openings area = 3 m²
- Waste allowance = 5 %
- Price per block = 2.2
the calculator returns:
- Blocks required: 268
- Blocks per m²: 9.88
- Net wall area: 25.8 m²
- Mortar volume: 0.31 m³