Concrete Block Calculator — CMU Wall Estimator
Enter your wall length, height and any openings to find out how many concrete blocks (CMU) and how many bags of mortar you need.
m
m
m²
Block type
%
12.5 blocks/m² · 14.4 m² net area
- 1
Gross wall area
6 × 2.4 = 14.4 m² - 2
Blocks needed
14.4 × 12.5 × 1.05 = 189Rounded up to a whole number; includes waste allowance.
How does this calculator work?
Find net wall area (L × H minus openings), divide by 0.08 m² per block to get 12.5 blocks/m², then multiply by (1 + waste%). Mortar is about 0.013 m³ per square metre, or roughly one 25 kg bag per 1.3 m² of wall. Round every count up when ordering.
Formula
How this is calculated
A standard concrete masonry unit (CMU) has a nominal face dimension of 400 mm wide × 200 mm tall (approximately 16" × 8"), including the 10 mm mortar joint. This gives 12.5 blocks per square metre of wall face. The calculator first finds the net wall area — wall length × height minus the area of any door and window openings — then multiplies by the block density and a waste factor (typically 5% for straight walls, more for corners and complex patterns).
Mortar consumption is estimated at 0.013 m³ of mortar per square metre of wall, which is a typical value for standard CMU laid with type S or type N mortar at a 10 mm joint. Dividing by the yield of a 25 kg premix bag (about 0.017 m³ of mortar) gives the bag count, rounded up.
The 6", 8" and 12" CMU sizes share the same 400 × 200 mm nominal face; the number you choose affects only wall thickness, not the block or mortar count. The estimate assumes single-wythe construction (one block thick). For double-wythe or reinforced walls, multiply the block count by the number of wythes and increase mortar accordingly.
Frequently asked questions
Standard CMU blocks with a 400 × 200 mm nominal face (including the mortar joint) cover 0.08 m² each, giving 12.5 blocks per square metre. Half-blocks (200 × 200 mm) give 25 per square metre.
Type S mortar (1 part cement : 0.5 part lime : 4.5 parts sand) is the most common for below-grade and exterior CMU walls. Type N (1:1:6) suits interior or above-grade non-load-bearing walls. This calculator uses a generic mortar volume estimate of 0.013 m³/m².
No — this calculator covers blocks and bedding mortar only. If your wall requires cores filled with concrete grout around rebar, use the Concrete Block Fill Calculator to add that volume.
Also known as
TG we-Calculate Editorial Team. (2026). Concrete Block Calculator — CMU Wall Estimator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/concrete-block-calculator
TG we-Calculate Editorial Team. "Concrete Block Calculator — CMU Wall Estimator." TG we-Calculate. 2026. https://we-calculate.com/calculator/concrete-block-calculator.
TG we-Calculate Editorial Team, "Concrete Block Calculator — CMU Wall Estimator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/concrete-block-calculator
@misc{wecalculate_concrete_block_calculator, title = {Concrete Block Calculator — CMU Wall Estimator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/concrete-block-calculator}}, year = {2026}, note = {TG we-Calculate} }
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