Block Wall Calculator
Blocks, mortar and fill for a concrete block wall.
Result appears here
Fill in the fields and press Calculate.
Formula, calculation, assumptions and sources
Blocks = Net wall area (ft²) × 1.125
Mortar ≈ 3 ft³ per 100 block
Grout = Net area × 0.30 ft³/ft² × (cell spacing fraction) [8-in CMU]
Run the calculation to see each step with your own numbers.
A 40 × 8 ft wall, no openings, vertical cells 32 in o.c., 5% waste.
Blocks = 320 × 1.125 = 360 → order 378
Mortar ≈ 3.6 × 3 = 10.8 ft³ (≈ 22 bags)
Grout = 320 × 0.30 × 0.25 = 24 ft³ = 0.89 yd³
- Standard 8 × 8 × 16 in CMU, running bond, 3/8-in joints, face-shell bedding.
- Grout figure is NCMA's for 8-in units; a bond beam course adds grout not counted here.
- Rebar, bond beams, control joints, ties, flashing and any veneer are separate.
- Does a block wall need grout?
- An unreinforced garden wall doesn't. A structural or below-grade wall has vertical rebar in grouted cells (commonly 32 or 48 in o.c.) plus grouted bond beams — follow the structural drawings.
- How many blocks per square foot of wall?
- About 1.125 standard 8×8×16 in blocks per square foot of wall face — a nominal block covers 8/9 of a square foot. A 40 × 8 ft wall is around 360 blocks before waste.
- Which cells get grouted?
- Follow the structural drawings. An unreinforced garden wall needs none; a structural or below-grade wall grouts the vertical cells with rebar, commonly at 32 or 48 in o.c., plus the bond-beam courses.
Blocks / mortar / grout
Standard 16×8 in nominal CMU face (ASTM C90) with a 3/8-in mortar joint → 1.125 blocks per ft² of wall. NCMA TEK 14-1B. ≈ 2.5–3.0 ft³ of mortar per 100 standard CMU (face-shell bedding, 3/8-in joint). NCMA TEK 09-01A. Default 3.0. Grout per area: NCMA TEK 03-02A.
About the Block Wall Calculator
The Block Wall Calculator gives the blocks, mortar and cell grout for a concrete block wall in one calculation, from the wall size and how many cells are grouted. It assumes standard 8×8×16 in units in running bond. Rebar, bond beams, control joints and any veneer are separate. For grout only, use the Concrete Block Fill Calculator; for the block count alone, the Concrete Block Calculator.
What you enter
- Wall length
- Wall height
- Openings to deduct
- Cells grouted
- Waste allowance — Default 5%. Adjust to your own allowance — the exact figure is always shown too.
What you get back
- Blocks (8×8×16) — shown as the exact figure and, separately, a recommended figure with your waste allowance added.
- Mortar — ≈ 3 ft³ per 100 block. A bag of mortar mix ≈ 0.5 ft³.
- Grout for filled cells — 0 if unreinforced. 1 yd³ ≈ 45 bags of 80 lb grout mix.
The formula, a worked example, the assumptions behind it and the sources are shown in full below the calculator.
Related calculators
- Concrete Block Calculator — Number of concrete masonry units (blocks) for a wall of a given area.
- Concrete Block Fill Calculator — Grout volume needed to fill the cores of a concrete block wall.
- Mortar Calculator — Mortar quantity for a brick or block wall.
- Rebar Calculator — Rebar quantity, spacing and lineal feet for a slab or footing grid.
Part of the Masonry calculators.