Concrete Block Calculator
Enter your wall's length and height to count the standard concrete blocks you'll need.
A standard concrete block (CMU) has a nominal face of 16 by 8 inches, which covers 0.889 square feet, so a wall needs about 1.125 blocks per square foot. Multiply the wall area in square feet by 1.125, then add 5–10% for waste and breakage.
How to Use This Calculator
Enter the total length and height of the wall in feet. The calculator uses the standard nominal block size of 16 by 8 inches — the most common CMU in the United States — to work out how many blocks cover that area.
Add a waste margin for blocks lost to cutting at corners and openings, and to breakage. Five to ten percent is normal. For a wall with many openings, subtract the door and window areas from the wall area first for a tighter estimate.
How the Calculation Works
A nominal 16-by-8-inch block presents a face of 128 square inches. Since a square foot is 144 square inches, each block covers 128 ÷ 144 = 0.889 square feet, which means you need 144 ÷ 128 = 1.125 blocks to cover one square foot.
Multiplying the wall area in square feet by 1.125 gives the base block count. The nominal size already includes an allowance for the mortar joint, so you do not subtract for mortar separately.
blocks per ft² = 144 ÷ (16 × 8) = 1.125
Worked Example
For a wall 20 feet long and 8 feet high, the area is 20 × 8 = 160 square feet. Multiply by 1.125 blocks per square foot: 160 × 1.125 = 180 blocks.
Add a 10% waste margin: 180 × 1.10 = 198 blocks. Order 198, or round up to a convenient quantity for delivery.
Assumptions and Limitations
- Assumes standard nominal 16×8-inch blocks; half-height or specialty blocks differ
- The nominal size already accounts for the mortar joint
- For walls with large openings, subtract door and window areas first
- Does not estimate mortar, rebar or fill — block count only
Who Uses a Concrete Block Calculator
Masons and DIY builders use this when laying a CMU wall — a foundation stem wall, retaining wall, garage, or garden wall. Enter the wall's length and height to count the standard blocks needed, with waste included, before ordering from the yard. Getting the count right up front means fewer trips back for more block, a tighter materials budget, and an accurate figure to price the job or check a supplier's quote.
Related Calculators
Cubic Yard Calculator
Convert length, width and depth into cubic yards for concrete, gravel, dirt or mulch.
Open calculator →Asphalt Calculator
Estimate tons of hot-mix asphalt (blacktop) for a driveway or lot.
Open calculator →Sand Calculator
Estimate cubic yards and tons of sand for a project.
Open calculator →Wainscoting Calculator
Estimate linear feet, boards and panel area for a room.
Open calculator →Frequently Asked Questions
How many concrete blocks are in a square foot?
About 1.125. A standard 16-by-8-inch block covers 0.889 square feet, so one square foot needs 144 ÷ 128 = 1.125 blocks.
Do I need to subtract for mortar joints?
No. The nominal 16-by-8-inch size already includes the standard 3/8-inch mortar joint, so the 1.125-blocks-per-square-foot figure accounts for it.
How much waste should I allow for block?
Add 5–10% for blocks cut at corners and openings and for breakage in handling. Complex walls with many openings sit at the higher end.
How many blocks are in a standard 8-foot-high wall?
About 9 courses of blocks per 8 feet of height, and 1.125 blocks per square foot overall. A 20-by-8-foot wall needs roughly 180 blocks before waste.
Does this include mortar and rebar?
No, it counts blocks only. As a rough guide, plan about three standard bags of mortar per 100 blocks, and size rebar and grout fill per your building code.
Looking for a different calculator?
CalculatorPlus has free tools across finance, construction, math, health and more — each one showing the formula and a worked example.