Concrete Block Calculator: Blocks, Cost and Wall Price

How to count blocks

A standard concrete masonry unit (CMU) measures 7⅝ × 7⅝ × 15⅝ in. With a ⅜ in mortar joint it takes up a 16 × 8 in space on the wall face: 0.889 square feet. That makes 1.125 blocks per square foot of wall.

Blocks = (wall length × wall height − openings) × 1.125

The count is the same for 6, 8 and 12 in thick blocks, because they share the 16 × 8 in face. Add about 5% for cuts and breakage.

Blocks for common walls

Wall	Area	Blocks	Materials	Installed
10 × 4 ft	40 sq ft	45	$145–$215	$605–$785
20 × 4 ft	80 sq ft	90	$285–$435	$1,210–$1,570
20 × 6 ft	120 sq ft	135	$430–$650	$1,810–$2,350
30 × 6 ft	180 sq ft	203	$645–$975	$2,720–$3,530
40 × 8 ft	320 sq ft	360	$1,150–$1,730	$4,840–$6,280

What a block wall costs

Homewyse puts an installed concrete block wall, set with mortar on an existing foundation, at $15.11–$19.61 per square foot (national average, May 2026)^[1]. Its materials line, blocks and mortar at non-discounted retail prices, comes to $462.77–$698.24 for a 129 sq ft wall: about $3.59–$5.41 per square foot. The footing under the wall is extra.

Retaining walls over about 4 ft, and any wall that carries a load, usually need engineering and a permit. Ask your building department before you buy blocks.

Frequently asked questions

How many concrete blocks do I need per square foot?

1.125. A standard block face is 16 × 8 in with a 3/8 in mortar joint, which covers 0.889 sq ft, so 1 ÷ 0.889 = 1.125 blocks per square foot.

How many blocks for a 20 ft wall 4 ft high?

80 sq ft × 1.125 = 90 blocks, plus about 5% for cuts and breakage.

How much does a concrete block wall cost?

Homewyse puts an installed block wall at $15.11–$19.61 per square foot (May 2026), with blocks and mortar alone about $3.59–$5.41 per square foot. A 20 × 4 ft wall comes to about $1,210–$1,570 installed.