Concrete Block Calculator
Work out how many concrete blocks a wall needs from its length and height, leaving out doors and windows and allowing for mortar and breakage.
The block's actual size, without mortar. A block sold as 16 × 8 in is really 15⅝ × 7⅝ in, so with a ⅜ in joint it covers 16 × 8. Measure one if you're not sure.
Blocks
426
- Blocks per sq ft
- 1.125
- Wall area
- 360 sq ft
A 40 × 10 ft wall less 40 sq ft of openings needs about 426 blocks of 15.625 × 7.625 in.
How it's worked out
- Wall area
40 × 10 − 40360 sq ft - One block with mortar
(15.63 + 0.375) × (7.63 + 0.375) ÷ 1440.8889 sq ft - Blocks
360 ÷ 0.8889 × 1.05, rounded up426
The formula
Blocks = (wall area − openings) ÷ face area of one block with mortar × (1 + breakage)
Worked example
A 40 × 10 ft wall with 40 sq ft of openings is 360 sq ft. A 15⅝ × 7⅝ inch block (sold as 16 × 8) with 3/8-inch joints covers 16 × 8 = 128 square inches, or 0.889 sq ft, so 360 ÷ 0.889 × 1.05 = 426 blocks.
Enter the block's actual size, not the size it's sold as. Sizes vary by country: many blocks sold as 400 × 200 mm are 390 × 190 mm, laid with a 10 mm joint.
Questions people ask
How many blocks per square foot?
1.125 standard blocks per square foot. A block sold as 16 × 8 inches is really 15⅝ × 7⅝ inches, so with a 3/8-inch mortar joint each one covers exactly 16 × 8 inches.
How many blocks for a 40 × 10 ft wall?
About 426 standard 16 × 8 inch blocks, after leaving out 40 sq ft of openings and adding 5% for breakage.
Does block thickness matter?
Not for the count: the number depends on the face size. Thickness matters for strength and cost.
About this calculator
Formula and rules last checked 25 October 2026Written and tested by the CalculatorDex teamReport a problem