Concrete Block Calculator: measuring notes and method
Count wall faces by block type
Use the face dimensions of the chosen block and the joint thickness. Split walls by thickness or block type even when their face sizes match. Half blocks and corner units need a separate schedule.
Do not infer core fill from block count
Concrete used to fill hollow cores depends on the actual unit and reinforcement arrangement. This calculator counts wall units only; it does not calculate grout, core fill, lintels or reinforcement.
Formula
Unit module = (unit length + joint) × (unit height + joint). Count = net area ÷ module, with waste, rounded up.
Worked examples in metric and imperial units
Illustrative values match Reset example and stay fixed when you edit the calculator. Both columns describe the same calculation; converted inputs are rounded.
Metric worked example
- Total surface area
- 24 m²
- Openings / excluded area
- 0 m²
- Unit length
- 390 mm
- Unit height
- 190 mm
- Mortar joint
- 10 mm
- Waste allowance
- 5 %
Blocks to buy: 315
Imperial worked example
- Total surface area
- 258.3339 ft²
- Openings / excluded area
- 0 ft²
- Unit length
- 15.3543 in
- Unit height
- 7.4803 in
- Mortar joint
- 0.3937 in
- Waste allowance
- 5 %
Blocks to buy: 315
Follow the calculation
Lengths in this working are in metres.
- Net area = 24 − 0 = 24 m².
- Module area = (0.39 + 0.01) × (0.19 + 0.01) = 0.08 m².
- Divide net wall area by that module, multiply by 1.05 and round up to whole units.
Reviewed 19 October 2026. How calculations are checked · Report a correction