Concrete Block Calculator

What is a concrete block calculator?

A concrete block calculator tells you how many concrete masonry units (CMUs) you need to build a wall of a given size. Instead of measuring and counting blocks by hand, you enter the wall’s length and height in feet and the calculator returns the number of standard blocks to buy.

It is the first estimate any masonry project starts with: knowing the block count lets you price out the job, order a single delivery, and avoid both running short mid-course and overpaying for surplus.

What counts as a “standard” block?

This calculator assumes a standard 16-inch by 8-inch block face. That is the nominal face size used across most of North America, and crucially it already includes the mortar joint around each block. A real CMU is closer to 15⅝ in by 7⅝ in, but the missing ⅜ in on each dimension is exactly the space the mortar fills, so the nominal 16 × 8 figure is what you use for coverage math.

One nominal block face therefore covers:

How does the calculator work?

First, the wall area is converted into square inches. Each foot is 12 inches, so a wall that is $L$ feet long and $H$ feet high has an area of:

Then the number of blocks is the wall area divided by the area each block covers, rounded up to the next whole block (you cannot buy a fraction of a block):

The calculator also reports the wall area in square feet ($A_{\text{ft}^2} = L \times H$) so you can sanity-check the dimensions you entered.

A handy shortcut hides in the constants: $144 / 128 = 1.125$, so a wall needs about 1.125 blocks per square foot, or roughly 9 blocks for every 8 square feet of wall.

Worked examples

A 10 ft by 8 ft wall. The area is $10 \times 8 = 80$ sq ft. In square inches that is $80 \times 144 = 11{,}520 \text{ in}^2$, and dividing by 128 gives exactly 90 blocks.

A 20 ft by 8 ft wall. Doubling the length doubles the area to $160$ sq ft, so you need $160 \times 144 / 128 =$ 180 blocks.

A 5 ft by 5 ft wall. The area is $25$ sq ft. The math gives $25 \times 144 / 128 = 28.125$, which rounds up to 29 blocks — the partial 29th block covers the leftover sliver of wall.

Practical notes

• Buy extra for waste. The count above is the bare minimum. Add roughly 5–10% for cuts at corners, openings, and breakage. On the 90-block wall, that means picking up about 95–99 blocks.
• Subtract large openings. This estimator does not deduct doors or windows. For a big opening, compute its area in square feet, multiply by 1.125, and subtract that many blocks from the total.
• Mortar and reinforcement are separate. The block count does not include mortar mix, rebar, or grout for filled cores — budget those alongside the blocks.
• Pair it with related tools. Once you know the block count, estimate the poured footing with the concrete volume calculator, check your wall area against a square footage calculator, or size the base fill with the gravel calculator.

Frequently asked questions

Does the 16 × 8 size include mortar? Yes. The nominal 16-by-8-inch dimensions already account for a standard ⅜-inch mortar joint, so you do not add anything extra for it.

What if my blocks are a different size? This tool is built for the standard 16 × 8 face. For an 8 × 8 half-height block or a metric unit, the coverage per block changes and the count would differ — divide your wall area in square inches by your block’s actual face area instead of 128.

How many blocks per square foot? About 1.125, because $144 / 128 = 1.125$. Multiply your wall’s square footage by 1.125 and round up for a quick mental estimate.