The model, stated exactly
Every standard block in the chart is made 3/8 of an inch smaller than its nominal size in each dimension, so that the block plus one 3/8-inch mortar joint equals the nominal size: actual = nominal − 3/8 inch. The face of a standard 8×16 block is therefore 8 × 16 = 128 square inches = 0.889 square feet, and the coverage rate is 1 ÷ 0.889 = 1.125 blocks per square foot. Wall area = wall length × wall height (in feet). Exact blocks = wall area × 1.125. Buy count = exact blocks × (1 + waste ÷ 100), rounded up to the next whole block — you cannot buy half a block, and rounding down would leave you short. This rate assumes full-size 8×16 faces throughout; half blocks, corners, and lintels are handled as notes below, not folded into the count.
Standard concrete block sizes
Nominal size is width × height × length in inches, where width is the wall thickness. Actual size is nominal minus the 3/8-inch mortar joint in every dimension. Weights are typical ranges, lightweight to normal-weight concrete, and vary by manufacturer and mix — confirm with your supplier before ordering by the pallet.
| Nominal size (in) | Actual size (in) | Typical weight | Common uses |
|---|
| 4 × 8 × 16 | 3-5/8 × 7-5/8 × 15-5/8 | 15–22 lb | Partition walls, veneer backup, garden edging |
| 6 × 8 × 16 | 5-5/8 × 7-5/8 × 15-5/8 | 22–33 lb | Interior load-bearing walls, partitions |
| 8 × 8 × 16 | 7-5/8 × 7-5/8 × 15-5/8 | 28–43 lb | Exterior walls, foundations, the standard workhorse block |
| 8 × 8 × 8 (half block) | 7-5/8 × 7-5/8 × 7-5/8 | 14–22 lb | Ending courses, corners, and openings where a full block will not fit |
| 12 × 8 × 16 | 11-5/8 × 7-5/8 × 15-5/8 | 43–60 lb | Heavy foundations, retaining walls, commercial walls |
Special shapes, not in the count: lintel blocks (U-shaped, also called bond-beam blocks) carry a poured concrete beam over openings and along the top course, and bond-beam blocks tie a wall together at the top. Order them separately by the opening or by the run — the calculator counts standard stretcher blocks only, so add lintels and bond beams to your order on top of the buy count. Corner blocks and half blocks likewise come out of the same wall length: a good rule is to allow one half block per course end, and to buy a few extra halves rather than cutting full blocks on site.
The worked example, line by line
Setup: wall 10 feet long, 8 feet high, waste 5%.
Line 1 — wall area. 10 × 8 = 80.0 square feet.
Line 2 — exact blocks. 80.0 × 1.125 = 90.0 blocks.
Line 3 — with waste. 90.0 × 1.05 = 94.5, rounded up to 95 blocks to buy.
Try these
Long wall: 20 by 8 feet. Area is 160.0 square feet, exact blocks are 180.0, and 5% waste gives 189 blocks exactly (180.0 × 1.05 = 189.0, no rounding needed).
More waste: 10 by 8 feet at 10%. Area is still 80.0 square feet and exact blocks still 90.0, but 10% waste gives 90.0 × 1.10 = 99 blocks to buy. Walls with many openings, corners, or short runs deserve the higher allowance.
Half blocks for the ends. A 10-foot wall run needs a half block wherever a course ends at a corner or opening — roughly one per course end. At 12 courses, a wall with two ends needs about 24 half blocks across the wall if every course is capped, though in practice many ends are handled by alternating full and half courses. Buy halves separately; do not subtract them from the full-block count unless your layout already accounts for them.
Output · formula · meaning
| Output | Formula | What it means |
|---|
| Wall area | Length × height | 80.0 sq ft at the defaults — the face of wall to cover. |
| Blocks per sq ft | 1 ÷ (8 × 16 ÷ 144) | 1.125 — one 8×16 face covers 0.889 sq ft, so each square foot needs 1.125 blocks. |
| Exact blocks | Wall area × 1.125 | 90.0 at the defaults — the perfect-world count, before cuts and breakage. |
| Blocks to buy | Exact blocks × (1 + waste ÷ 100), rounded up | 95 at the defaults — the order quantity, with 5% waste and rounding up. |
Who uses this
- The homeowner building a garden wall: enters 10 by 4 feet and learns the wall needs 45 blocks exactly, 48 to buy — a Saturday project, not a pallet order.
- The DIYer pricing a shed foundation: enters the foundation run and gets a buy count before calling the yard, so the quote covers blocks, not guesses.
- The contractor checking a takeoff: runs the wall through the 1.125 rate to sanity-check a supplier's count, and spots a short order before the truck leaves.
- The student or apprentice learning masonry: sees why a nominal 8×8×16 block measures 7-5/8 inches, and why the mortar joint is part of the size, not an error.
Accuracy & limitations
The count is exact for a plain rectangular wall of standard 8×16 faces at the waste rate you enter. It does not subtract doors, windows, or other openings — measure each opening's area, multiply by 1.125, and subtract that from the exact count before applying waste, or simply let the waste allowance absorb small openings. It does not count mortar, reinforcement, lintels, bond beams, caps, or footings, and it counts no half blocks: add those separately using the notes above. Weights are typical ranges only — lightweight and normal-weight mixes differ by a third or more, and the only weight that matters for your order is your supplier's. Error policy: missing, non-numeric, or out-of-range inputs are reported as errors rather than calculated.
Cite this calculatorBright Side Kit. “Concrete Block Size Chart & Calculator — Bright Side Kit.” brightoolbox.com, 2026.Bright Side Kit. "Concrete Block Size Chart & Calculator." https://brightoolbox.com/concrete-block-size-chart/ Accessed October 24, 2026.
Embed this calculatorPaste this into any web page to embed the live calculator. The “Powered by Bright Side Kit” link below it must stay intact.