Concrete Cinder Block Calculator

Cinder block wall: block and mortar counts by size

Each row uses 20 cm blocks, plus 5% extra (a US guide's figure). Mortar is 8.3 bags of 30 kg per 100 blocks, with nothing added.

Weight: 223 kg per m² of wall, with mortar (Brampton Brick). Cost: $4.24 a block and $12.42 a bag, before tax.

Metric blocks, metric count

Canadian 20 cm blocks are metric. With joints, each one covers 400 × 200 mm. That is 12.5 per m², or 1.16 per sq ft in either unit.

Blocks sized in inches give 1.125 per sq ft, about 3% fewer. US guides and Shaw Brick (Nova Scotia) use that count.

Concrete blocks to build a house or shed foundation

Add up the outside walls, then use that as one long wall. A 30 × 40 ft basement has 140 ft of wall. At 8 ft high, that takes about 1,366 blocks with 5% extra, before doors and windows. A foundation holds up the house, so check your local building rules or ask a builder or engineer.

A block wall under a shed works the same way. Type the shed's four sides as the length and the wall's height. Some sheds sit on blocks as piers, not on a wall. Under a 1-storey building, piers go no more than 3.5 m (about 11.5 ft) apart along the framing. That is the building code (Part 9) rule in BC and Ontario. Check with your city.

Cinder blocks for a raised garden bed

Measure all the way around the bed for the length. One course of 20 cm blocks is 200 mm high with its joint. A 4 × 8 ft bed has 24 ft of sides. One block high, it takes about 20 blocks with 5% extra. Type 0.66 ft (0.2 m) as the height for one course.

Metric block sizes and weights

Concrete blocks are also called cinder blocks or CMU, short for concrete masonry units. Canadian blocks come in 5 widths. All are 190 mm high and 390 mm long. An "8 in" block is the 20 cm size.

Size: width × height × length. Weights: Brampton Brick (Ontario). Pallets: one Nova Scotia maker's smooth, bullnose and utility blocks. Prices: Ontario stores, before tax; the 30 cm price is from 1 store only.

Block for foundations must be at least 15 MPa, says the building code (Part 9).

Mortar: how much, and which type

Pre-mixed mortar has the sand in the bag. A 30 kg bag makes about 18 L, say Sakrete, Bomix and King Block.

Sakrete Canada says one bag lays about 12 blocks. But its sheet shows a smaller 15 × 20 × 30 cm block. Quikrete's 30 kg page at Home Depot also says 12 standard blocks.

Only two makers give a count, so treat it as rough. We add nothing on top of it.

From Table 9.20.3.2.-A, Part 9 (BC Building Code 2018 text).

Mixing your own

You can mix bagged masonry cement with sand instead. The code mix is 1 part masonry cement to 2¼ to 3 parts damp, loose sand.

Joints are 10 mm thick, give or take 5 mm. King Block, a Type S mortar, is not for filling block holes.

What blocks and mortar cost

• 20 cm block: $4.24, the middle of only 3 stores ($4.19–$5.24).
• Type S mortar, 30 kg: $12.42, the middle of 4 stores.
• Type N (or unnamed) mortar, 30 kg: $11.67, the middle of only 3 stores.
• Masonry cement, 30–33 kg: $23.66, the middle of only 3 stores. Add your own sand.

All are Ontario prices from Oct 2026, before tax. Prices in other provinces may differ.

The calculator counts blocks for a retaining wall too. But a wall that holds back soil or carries weight needs a plan. Check your local building rules or ask a builder or engineer.