BuildRight

Block Wall Calculator

Wall area converted into a block count, using the standard 8×16 inch CMU coverage rate.

Wall area (sq ft)

Waste factor (%)

Blocks needed

248

Based on standard 8×16 in concrete block (1.125 blocks per sq ft including mortar joints).

What you entered

Wall area (sq ft): 200Waste factor (%): 10

1
Base block count (1.125 blocks/sq ft)
200 × 1.125= 225 blocks
2
Add 10% waste
225 × 1.10= 248 blocks

Result

Blocks needed: 248

A 200 sq ft wall needs about 248 concrete blocks, including a 10% waste allowance.

Concrete blocks needed for typical block-wall projects at 8 x 16 inch CMU coverage

Counts use the standard 8 x 16 inch concrete masonry unit rate this calculator applies, 1.125 blocks per square foot including the mortar joint, with wall area taken as length times height and no openings deducted.

Wall (project and size)	Wall area (sq ft)	Blocks, no waste	Blocks at 10% waste	Blocks at 15% waste
Garden wall, 20 x 3 ft	60	68	75	78
Retaining wall, 25 x 4 ft	100	113	124	130
Garden wall, 30 x 4 ft	120	135	149	156
Retaining wall, 40 x 4 ft	160	180	199	207
Shed wall, 12 x 8 ft	96	108	119	125
Garage wall, 24 x 8 ft	192	216	238	249
Basement wall, 30 x 8 ft	240	270	297	311
Basement wall, 40 x 8 ft	320	360	397	414
Foundation run, 50 x 8 ft	400	450	496	518

Block count only. A real wall also needs half blocks and corner blocks at every opening and corner, mortar at roughly 3 bags of 80 lb mix per 100 blocks, and for structural or retaining walls vertical rebar with grout fill, none of which is counted here. Wall height in courses is height in inches divided by 8, so a 4 ft wall is 6 courses and an 8 ft wall is 12. Use 10 percent waste on a straight run and 15 percent where there are corners, openings, or cuts. Retaining walls hold back soil and water pressure and are a structural design problem: have the footing, reinforcement and drainage specified by an engineer or your local building department rather than sized from a block count.

Standard CMU coverage

This uses the common 8×16 inch concrete masonry unit (CMU) at 1.125 blocks per square foot, accounting for the mortar joint — half blocks, corner blocks, and other specialty units may be needed separately at openings and corners.

Don't forget mortar and rebar

This calculator covers block count only — a block wall also needs mortar mix and typically vertical rebar with grout fill at regular intervals for structural walls, which this doesn't estimate.

Frequently asked questions

My wall is 20 ft long and 6 ft tall — how many blocks do I need?

About 135 blocks (20 x 6 = 120 sq ft x 1.125 blocks/sq ft = 135). Add 5-10% for cuts and breakage — order about 145-150 blocks.

How is this different from the brick calculator?

Concrete blocks (CMUs) are much larger than bricks — 8x16 inches vs. roughly 4x8 inches. You need about 1.125 blocks per square foot versus 6.75 bricks per square foot. Blocks are faster to lay but create a different aesthetic.

Do I need rebar in a block wall?

Structural and retaining walls typically require vertical rebar every 32-48 inches with grout fill, plus horizontal rebar in bond beams. Non-structural garden walls may not need rebar. Check your local building code for requirements.