Counting blocks by wall area
A standard 8×8×16 CMU shows 8 inches of height and 16 inches of face per block, so each block covers about 0.89 square feet of wall — the industry rounds to 1.125 blocks per square foot. Multiply wall area by that, add 5–10% for breakage and the blocks you'll cut around corners and openings.
Mortar goes with the count
Plan on roughly 3 bags of mortar per 100 blocks (see the block mortar calculator), plus one cap block per linear foot if the wall gets capped. Cores that will be filled with rebar and concrete change the concrete order, not the block order — count blocks first, then run the concrete block fill calculator for the poured cores.
How many blocks per square foot?
A standard 8 × 8 × 16 inch concrete masonry unit (CMU) presents an 8-inch height and a 16-inch face, so its nominal coverage is 16 × 8 = 128 square inches, or 0.889 square feet. Dividing one square foot by that figure gives 1.125 blocks per square foot — the number every block estimator starts from.
| Wall area | Blocks (nominal) | Order with 5% waste |
|---|---|---|
| 100 sq ft | 113 | 119 |
| 200 sq ft | 225 | 237 |
| 300 sq ft | 338 | 355 |
| 500 sq ft | 563 | 592 |
| 1,000 sq ft | 1,125 | 1,182 |
Three worked examples
Example 1 — a 50 ft × 6 ft garden wall
Area: 50 × 6 = 300 sq ft. Blocks: 300 × 1.125 = 338 blocks. Add 5% for cuts at the ends and around any opening: 338 × 1.05 ≈ 355. Mortar: at roughly 3 bags per 100 blocks, 355 blocks needs about 11 bags. A single course of 8-inch block also means the wall is 8 inches thick — if you want a 6-inch wall, the count changes because 6-inch CMUs have different face dimensions.
Example 2 — a 20 ft × 8 ft garage wall
Area: 160 sq ft. Blocks: 160 × 1.125 = 180, plus 5% = 189 blocks. This wall is short enough that the waste allowance mostly covers corner cuts and the half blocks at each end of alternating courses. A novice mistake is to order exactly 180 and run short by a dozen at the top course.
Example 3 — a long run with an opening
A 100 ft wall 5 ft high with a 3 ft × 7 ft door: gross area 500 sq ft, minus the opening 21 sq ft = 479 sq ft. Blocks: 479 × 1.125 ≈ 539, plus 5% ≈ 566. Note what happened here — the wall got longer but the block count barely moved, because depth claims in the estimator are about area, not length. Always work in square feet.
Mortar, cores and grout
- Mortar: plan on roughly 3 bags of mortar per 100 blocks for standard 3/8-inch joints. A 500-block wall therefore needs about 15 bags.
- Grout (core fill): a fully grouted wall consumes a surprising amount of concrete — the number of blocks one cubic yard fills depends on the block's core geometry and how it is laid (bond beams and lintels consume far more than a straight run). Take the figure from the block manufacturer's grout table rather than a generic rule.
- Rebar: vertical reinforcement typically runs on a grid set by the engineer — commonly every 32 or 48 inches horizontally in a reinforced wall, with a bar in every core of a bond beam.
- Cap blocks: if the wall is capped, allow one cap block per linear foot of wall — a 50 ft wall takes about 50 caps.
Reinforced walls are an engineering question, not an estimating one: the spacing of bars and the grout percentage come from the structural design, and the block count is the only part this calculator can answer for you.
Ordering mistakes that cost a second delivery
- Using 1.125 for every block size. That figure is specific to the 8 × 8 × 16 CMU. A 12 × 8 × 16 block covers the same face (16 × 8) but weighs half again as much and costs more — the count is the same, the load and price are not. A 4-inch or 6-inch block changes the face dimensions entirely.
- Forgetting the waste allowance. Walls need cutting at corners, at openings, and at the top course if the height is not a multiple of 8 inches. Five per cent is the minimum; 10% is safer for a wall full of openings.
- Estimating by length. "One block every 16 inches" sounds equivalent to 1.125 per square foot, but it ignores the height dimension and the mortar joints, and it drifts badly on tall walls.
- Mixing metric and imperial. Blocks sold in metric markets are typically 390 × 190 × 190 mm with a 10 mm joint, which works out at about 12.5 blocks per square metre. The 1.125-per-square-foot figure does not transfer.
- Ignoring the pallet size. A standard 8 × 8 × 16 CMU pallet commonly holds 75 to 90 blocks depending on the manufacturer, so a 566-block order is roughly 7 pallets — which is what determines your delivery truck and your unloading plan.
Tools for laying block
Once you know the block count and the mortar volume, this is the kit the job actually calls for. All standard masonry tools — nothing project-specific.
- Masonry trowel — A 10-inch London or Philadelphia pattern trowel spreads both bed and head joints. One per mason on the wall.
- Mortar mixing tub and hoe — Past the first few bags, mixing in a tub or wheelbarrow keeps the mortar workable far longer than a bucket does.
- 48-inch spirit level — Block courses go out of plumb quickly. A 4-foot level is the practical minimum for controlling a wall as it rises.
- Brick set chisel and hammer — Half blocks at corners and openings cut far cleaner with a brick set than with a grinder — and without the dust.
As an Amazon Associate I earn from qualifying purchases. The links above are affiliate links — if you buy through one, the price you pay is unchanged and a small commission helps keep these calculators free. Tools are listed because the job calls for them, not because of commission rates.
Sources and standards
Where these figures come from
Every formula on this page is implemented from the published reference material below. Where a value depends on a regional code, the calculator lets you override it rather than assuming one jurisdiction.
- ASTM International — C94 for ready-mixed concrete, C150 for cement and C143 for slump testing.
- American Concrete Institute — ACI 318 code requirements and ACI 302 slab construction guidance.
- Portland Cement Association — mix design, yield and curing data published by the US cement industry.
Figures, formulas and reference tables last verified: 19 September 2026.