Concrete & Masonry

Concrete Block Calculator

Estimate nominal concrete masonry unit count from wall dimensions, openings, block face size and waste allowance.

Enter the finished wall length and height, subtract openings, then select the block's nominal face dimensions. The result rounds the order up to whole blocks.

Calculation and worked example reviewed 2026-11-12. See our calculation methodology.

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Concrete & Masonry

Enter your measurements

US UNITS

Wall length

Wall height

Door and window openings

sq ft

Nominal block face length

Nominal block face height

Waste allowance

Optional: Material Price ($ / unit)

YOUR ESTIMATE

198 blocks to order160 sq ft net wall

180 blocks before 10% waste.

Nominal face dimensions; verify block type and layout.

Formula and example

How this calculation works

This estimator converts your entered jobsite inputs (wall length, wall height, door and window openings, nominal block face length, nominal block face height, waste allowance) into consistent US trade units, computes the exact geometric baseline first, and then applies any selected waste or order allowance so you can verify both numbers before purchasing materials.

How does the concrete block calculator formula work?

Net wall area (sq in) = (wall length × 12 × wall height × 12) − opening area × 144; blocks = net area ÷ (nominal face width × nominal face height); order = ceil(blocks × (1 + waste% ÷ 100)).

(Concrete Block Calculator)

where:

Wall length – Entered in ft (default reference: $20 ft$ );
Wall height – Entered in ft (default reference: $8 ft$ );
Door and window openings – Entered in sq ft (default reference: $0 sq ft$ );
Nominal block face length – Entered in in (default reference: $16 in$ );
Nominal block face height – Entered in in (default reference: $8 in$ );
Waste allowance – Entered in % (default reference: $10 %$ );

The formula

Inputs to result

Worked example

Check the math

A 20 ft × 8 ft wall with no openings uses 8 × 16 in nominal blocks. At 10% waste: 160 sq ft ÷ (128 ÷ 144 sq ft) = 180 blocks; order 198.

Quick lookup chart

Nominal 8 × 16 CMU Block Count Reference by Wall Size

Based on standard 8 × 16 in nominal face area (128 sq in or 0.889 sq ft per block, 1.125 blocks per sq ft) before openings.

Wall Dimensions	Gross Wall Area	Exact CMU Count	Order w/ 10% Waste
10 ft × 8 ft	80 sq ft	90 blocks	99 blocks
20 ft × 8 ft	160 sq ft	180 blocks	198 blocks
30 ft × 8 ft	240 sq ft	270 blocks	297 blocks
40 ft × 10 ft	400 sq ft	450 blocks	495 blocks

Limits and field checks

Before you use this result

This is a face-area estimate. It does not calculate corners, bond beams, lintels, reinforced cells, cutting pattern or mortar. Use nominal modular dimensions, then verify the selected unit and layout with the supplier.

Use nominal modular dimensions (length + one 3/8 in mortar joint), such as 16 × 8 in for standard 15-5/8 × 7-5/8 in stretcher units.
Count corner blocks, bond-beam U-blocks, half-blocks, and precast lintels separately from standard field stretchers.
Estimate roughly 3 to 3.5 bags of premixed Type N or Type S masonry mortar per 100 standard 8 × 16 blocks, plus grout for reinforced cells.

Questions answered

Calculator FAQ

How many 8 × 16 blocks cover a square foot?+

The nominal face is 128 square inches, so one square foot requires 144 ÷ 128 = 1.125 blocks before waste.

How much does a standard 8x8x16 concrete block weigh?+

A standard nominal 8 × 8 × 16 inch concrete block (CMU) made from normal-weight aggregate weighs approximately 35 to 40 pounds (16 to 18 kg). Lightweight aggregate blocks weigh between 25 and 30 pounds.

Should openings be subtracted?+

Yes. Enter the combined area of doors and windows. Small openings or heavily cut edges may still create additional waste.