How Many Concrete Blocks Do I Need for a Wall?
Quick answer: multiply your wall area (length × height in feet) by about 1.125 — that's how many standard 16×8-inch concrete blocks fit, mortar joint included. A 100-square-foot wall needs about 113 blocks (≈119 with waste). The concrete block calculator does the count plus mortar and grout; here's how it works.
Why 1.125 blocks per square foot?
Concrete block sizes are nominal: a "16×8" block is really 15⅝ × 7⅝ inches, and the missing ⅜ inch is the mortar joint. So one block plus its joint covers a 16 × 8-inch face = 0.89 square feet, which works out to about 1.125 blocks per square foot of wall. Multiply your wall area by 1.125 and round up.
A worked example
A wall 20 feet long and 8 feet high:
- Area: 20 × 8 = 160 sq ft
- Blocks: 160 × 1.125 = 180 blocks, or about 189 with 5% waste
- That's 12 courses (96 in ÷ 8) of 15 blocks each
The concrete block calculator returns all of this, plus the mortar and optional grout.
Don't forget mortar and grout
- Mortar: plan on about three 80-lb bags per 100 blocks to lay them up — roughly 6 bags for our 189-block wall.
- Grout: structural and retaining walls often have some or all cores filled with grout (and rebar). A standard 8-inch block holds about 0.26 cubic feet of fillable core; turn on core fill in the calculator to estimate it.
Concrete block, cinder block, or CMU?
They're different names for the same units, and the count is identical. "Cinder block" is the older term, "CMU" (concrete masonry unit) the technical one. If you're building a stacked-block retaining wall instead — the kind with a lip that sets back each course — use the retaining wall calculator, which counts those segmental blocks and the backfill gravel.
Before you build
Order about 5% extra block for cuts at corners and openings. Structural walls, retaining walls, and walls over a few feet generally need engineering, rebar in grouted cores, and a permit — check your local code first. For the gravel footing base under the wall, the gravel calculator sizes it.
Frequently asked questions
How many blocks are in a 10x10 wall?+
About 113 standard 16×8-inch blocks for a 100-square-foot wall (1.125 blocks per square foot), or roughly 119 with a 5% waste allowance. Enter your wall size in the concrete block calculator for an exact count.
How many blocks per square foot?+
About 1.125 standard 16×8-inch concrete blocks per square foot of wall, because one block plus its mortar joint covers a 16×8-inch (0.89 sq ft) face.
How much mortar do I need for a block wall?+
Roughly three 80-lb bags of mortar per 100 blocks. The block calculator estimates the bags from your block count and lets you adjust for joint size.