Concrete Block Calculator
Concrete blocks are sold by the pack, and the count depends on the block face and the joint: a UK 440 × 215 mm block with 10 mm joints is 10 to the square metre, a US 8 × 8 × 16 in CMU about 12. Enter the wall size, deduct the openings, and this calculator returns the block count with waste, the packs to order and a mortar estimate.
Your measurements
Check your order
Your masonry order
- Check dimensions, openings and the material specification against the project plan.
- Confirm pack size or bag yield with the supplier and add the selected allowance only once.
- Plan delivery access, handling and the tools required by the chosen installation method.
Tools for this job
Measure the wall and openings before ordering blocks. Match the mortar bed and joint thickness to the block system and project specification.
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- Place mortar in beds and joints
Brick trowel
MARSHALLTOWN Philadelphia brick trowel
For placing and spreading mortar when laying bricks or blocks. Choose a blade size you can handle comfortably and keep the specified bed and joint thickness consistent.
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Short tape measure
STANLEY 25-foot tape measure
For checking lengths, widths and short runs before ordering. This is a 25-foot tape; use matching units in the calculator and check the scale on the selected model.
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Already have suitable tools? Reuse them. These are optional product suggestions, not a complete equipment list or a hands-on comparison. Amazon may redirect Amazon.com links to local products or search results. Amazon.nl links search for alternatives, which may differ in brand, size and specification. Check suitability, seller, delivery and any import costs on your chosen store before ordering.
How many concrete blocks do I need?
Blocks are counted from the face area of the wall: length × height, or the area you already know, less the openings. Divide by the face area of one block plus its mortar joint. A UK block is 440 × 215 mm, so with 10 mm joints it occupies 450 × 225 mm and there are 9.9 blocks in a square metre, which everyone rounds to 10. A US 8 × 8 × 16 in CMU is 16 × 8 in including its 3/8 in joint, so 1.125 per square foot or about 12.1 per square metre.
Add waste for the cuts at corners, at openings and along the top course, plus the odd block that breaks in the pack. 5% covers a plain run; 10% is realistic once there are openings. The result is rounded up to whole blocks and then to whole packs, because blocks are sold by the pallet and a short pack means a second delivery.
The formula
Blocks per square metre by format
The count does not change with block thickness: a 100 mm and a 215 mm block have the same face. Thickness changes the weight and the mortar, so choose the thickness first and then set the mortar rate to suit.
| Block | Face size | Joint | Per m² | Per sq ft |
|---|---|---|---|---|
| UK standard | 440 × 215 mm | 10 mm | 9.9, use 10 | 0.93 |
| UK standard, both leaves in block | 440 × 215 mm | 10 mm | 20 | 1.86 |
| US 8 × 8 × 16 in CMU | 15 5/8 × 7 5/8 in (397 × 194 mm) | 3/8 in | 12.1 | 1.125 |
| US 8 × 4 × 16 in half-high CMU | 15 5/8 × 3 5/8 in | 3/8 in | 24.2 | 2.25 |
| 390 × 190 mm (Australia, parts of Europe) | 390 × 190 mm | 10 mm | 12.5 | 1.16 |
Worked example
A garage side wall 6 m (20 ft) long and 2.4 m (8 ft) high in UK 440 × 215 mm blocks, single leaf, no openings. Area = 6 × 2.4 = 14.4 m². Blocks before waste = 14.4 × 10 = 144. Add 10% = 158.4, rounded up to 159 blocks. In packs of 72 that is 2.2 packs, so 3 packs: 216 blocks with 57 spare. Mortar = 14.4 × 10 L = 144 L, or 0.144 m³ before waste.
Put a 2 m² door opening in the same wall and the net area drops to 12.4 m²: 124 blocks before waste, 137 with 10%, which fits in 2 packs of 72 with 7 spare. One opening is often the difference between two pallets and three, so it is worth deducting openings properly.
Block thickness and weight
A pack of 72 dense 100 mm blocks weighs about 1.4 tonnes, so check that the lorry can set it down close to the wall. Aerated blocks are light enough to lay one-handed but need a weaker mortar or a thin-joint adhesive, and their own fixings.
| Thickness | Typical use | Dense solid block | Aerated block |
|---|---|---|---|
| 100 mm (4 in) | Inner leaf of a cavity wall, partitions, garden walls with piers | 18 to 20 kg | 4 to 7 kg |
| 140 mm (5.5 in) | Loadbearing walls, garages, retaining walls with piers | 25 to 28 kg | 6 to 10 kg |
| 215 mm (8.5 in) | Solid walls, foundations below ground, walls a brick thick | 39 to 43 kg solid, less if hollow | 9 to 15 kg |
What else the job needs
- Mortar: about 10 L per m² for 100 mm blocks. The mortar calculator adds waste and gives the cement and sand for your mix.
- A concrete footing under any loadbearing or freestanding wall: use the concrete calculator for the strip.
- Wall ties at 2.5 per m² (900 × 450 mm spacing) between the leaves of a cavity wall, plus cavity insulation and a damp-proof course.
- Lintels over every opening, bearing at least 150 mm on each side.
- Facing bricks for the outer leaf: count them with the brick calculator.
Mistakes that leave you short
- Counting one leaf when both are block. A cavity wall with a rendered or clad outer face is often block on both sides: choose both leaves.
- Using the UK figure of 10 per m² for US CMUs, which are smaller on the face and need about 12 per m².
- Forgetting the cuts at the top of a wall under a sloping roof, or the half blocks at every corner in stretcher bond.
- Ordering the exact number. Blocks chip at the corners in the pack, and one short pack costs a delivery.
- Ignoring the weight. Dense blocks arrive by the tonne; make sure there is somewhere flat to put the pallets and a route for the barrow.
Sources and assumptions
Block count is net wall area multiplied by units per m² and leaves, plus waste. A 440 × 215 mm face with 10 mm joints makes a 450 × 225 mm module, or about 9.88 blocks/m², rounded to 10 in the preset.
- Forterra: Thermalite product brochure: The manufacturer documents 440 × 215 mm faces for its standard-format blocks, with varying thicknesses, strengths and weights.
Before using this estimate
- The preset joint is conventional mortar, not thin-joint adhesive. Enter a custom rate for other unit sizes or joint systems.
- Hollow cores, piers, lintels, cut blocks and reinforcement are outside the count. Quantity alone does not determine the wall’s structural, thermal or fire performance.
Source notes reviewed . See how we check calculations and handle corrections.
Planning your order
Check the inputs before buying: measure the surfaces you need, then apply an allowance and round to whole packs. The guides include worked examples you can follow alongside this calculator.
Published by OrderEnough. This is a planning estimate: check the product specification and the assumptions above before ordering. Last updated . Read how we source our figures on the methodology page.