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Concrete block calculator

Block walls are a tiling problem with heavy rectangles. Face size (often 8×16 nominal) into wall area gives pieces; waste covers cuts and breakage; mortar bags follow a rough blocks-per-bag rule of thumb. This page counts units. It does not size bond beams, rebar schedules, or stamped walls.

ft
ft
in
in
5%
0510152025

+5% so you don't come up short

ORDER ESTIMATECMU
Blocks to buy189
Mortar bags6
Wall area160 sq ft
Waste5%
How it calculates
courses = ceil(height × 12 ÷ block H); per course = ceil(length × 12 ÷ block W); blocks = ceil(courses × per course × (1 + 5%)); mortar = ceil(blocks ÷ blocks/bag).

Estimate only — not a contractor bid. Confirm bag yields and local codes before you pour or order.

When to use

Garden wall or shed stem-wall shopping; comparing 8 in vs 4 in block counts; rough mortar bag runs.

When not to

Retaining walls over DIY height limits — engineering required. Split-face / glazed specialty units sold by unique coverage — use the carton.

Assumptions

Nominal 8×16 in face common default (actual face ~7-5/8 × 15-5/8 — use actual if you care about the last course). Waste default 5–10%. Mortar ≈ blocks ÷ blocks_per_bag (label wins).

Worked examples

Example 1

40 ft long × 4 ft high, 8×16 nominal, waste 5%
→ 3 courses × 30 blocks ≈ 90 → 95 blocks ordered; mortar from bag yield

Corners share blocks — rectangular plans need a corner adjustment if you count four walls naively.

Example 2

12 ft × 3 ft planter, waste 8%
→ scale courses × length; add pier blocks separately if used

How it calculates

Tile the wall face with block dimensions, add waste, then mortar from blocks-per-bag.

  1. Enter wall length and height.
  2. Set block face width and height (default 16 × 8 in).
  3. Set waste and blocks per mortar bag; read blocks and bags.
courses ≈ ceil(wall_height_in ÷ block_height_in)
blocks per course ≈ ceil(wall_length_in ÷ block_length_in)
blocks = courses × per_course × (1 + waste%)
mortar bags ≈ ceil(blocks ÷ blocks_per_bag)

Common traps

  1. Nominal vs actual — running bond depends on real face size.
  2. Openings — windows need lintels; subtracting area is not enough for structural.
  3. Half blocks still come from full units you cut.
  4. Grouted cells / rebar change mortar and grout, not only block count.

Next tool

Solid concrete wall pour → concrete calculator.

Rebar in cells → rebar calculator.

Pad under equipment → concrete pad calculator.

FAQ

(length ÷ block length) × (height ÷ block height), plus waste.

Related

Estimate only — not a contractor bid or engineered takeoff. Confirm bag yields and local codes before you pour or order.