Concrete Block Calculator — How Many Blocks for a Wall
Count the concrete blocks (CMU) for a wall from its length and height, minus doors and windows, with courses, waste and mortar bags for standard blocks.
Plan a block wall, foundation or garden wall by working out how many concrete masonry units (CMU, often called cinder blocks) to buy. Enter the wall length and height, subtract the openings and pick the block size. The calculator divides the wall area by the block’s face size including the mortar joint, adds an allowance for cuts and breakage, and for standard 8 × 8 × 16 in blocks estimates the bags of premixed mortar.
How to use this tool
- Choose feet or metres.
- Enter the wall length and height.
- Add up the area of any doors, windows or other openings and enter it.
- Choose the block size — the face size including the joint decides the count.
- Set the waste allowance and, optionally, the price per block.
Formula
Blocks = (L × H − openings) ÷ (block length × block height) × (1 + waste %)
Block sizes are nominal: a standard US block measures 15⅝ × 7⅝ in but takes up 16 × 8 in with its ⅜ in joint, so it covers 0.889 sq ft and you need 1.125 blocks per square foot. The 440 × 215 mm block used in the UK covers 450 × 225 mm with a 10 mm joint, about 9.88 per m².
Example
A 40 ft wall 6 ft high has 240 sq ft of face. At 1.125 standard blocks per sq ft that is exactly 270 blocks — 9 courses of 30. With 5% extra, buy 284 blocks. QUIKRETE rates an 80 lb bag of Mortar Mix at up to 13 standard blocks, so the maximum coverage gives a minimum estimate of 22 bags; lower coverage needs more.
Frequently asked questions
How many blocks are in a square foot?
1.125 standard 16 × 8 in blocks, or 2.25 half-high or half blocks. In metric, about 9.88 blocks of 440 × 215 mm or 12.5 blocks of 390 × 190 mm fill a square metre.
Does block width change the count?
An equal face size gives the same area estimate regardless of width. The mortar result here applies only to standard 8 × 8 × 16 in blocks; obtain the correct coverage for another width or bedding method.
Should I count corner blocks separately?
Prepare a course-by-course takeoff for corners, bond beams, lintels, bond pattern and cut pieces. The area result is a preliminary quantity and does not determine how many units of each type to purchase.
How much extra should I order?
Choose an allowance based on cuts, handling loss and reuse of cut pieces for your wall. The default 5% is an assumption rather than a guaranteed allowance for every layout.
Sources
Last updated: 2026-10-30