Concrete Block Calculator
Count concrete blocks (CMU) for a wall and estimate the mortar bags to lay them.
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What this tool does
Count concrete blocks (CMU) for a wall and estimate the mortar bags to lay them. All standard CMUs share the 16 × 8 in face module (1.125 blocks per sq ft); half blocks cover half that face. The mortar figure uses the published planning rate of about 37 standard blocks per 80 lb bag — confirm with your mortar brand.
How to use the Concrete Block Calculator
- Enter or select length in ft.
- Enter or select height in ft.
- Enter or select block size (nominal).
- Enter or select waste allowance (%).
- Read the calculated result; change any measurement to compare alternatives.
Formula
block face module = 16 × 8 in incl. joint = 1.125 blocks per sq ft; blocks = ceil(wall area × 1.125 × (1 + waste/100)); mortar bags ≈ blocks / 37
- length
- Length (ft, before metric conversion)
- height
- Height (ft, before metric conversion)
- block
- Block size (nominal)
- waste
- Waste allowance (%)
All standard CMUs share the 16 × 8 in face module (1.125 blocks per sq ft); half blocks cover half that face. The mortar figure uses the published planning rate of about 37 standard blocks per 80 lb bag — confirm with your mortar brand.
Worked example
For concrete block calculator, the following measurements illustrate the exact method: Length: 20; Height: 8; Block size (nominal): std; Waste allowance (%): 10.
Inputs
- Length20 ft
- Height8 ft
- Block size (nominal)8 × 8 × 16 in standard CMU
- Waste allowance (%)10
Result
- Blocks to buy199
- Blocks per square foot1.13
- Wall area160 sq ft
- Mortar bags (80 lb, approx.)6
Results explained
- Blocks to buy
- Blocks to buy from the formula above. All standard CMUs share the 16 × 8 in face module (1.125 blocks per sq ft); half blocks cover half that face. The mortar figure uses the published planning rate of about 37 standard blocks per 80 lb bag — confirm with your mortar brand.
- Blocks per square foot
- Blocks per square foot from the formula above. All standard CMUs share the 16 × 8 in face module (1.125 blocks per sq ft); half blocks cover half that face. The mortar figure uses the published planning rate of about 37 standard blocks per 80 lb bag — confirm with your mortar brand.
- Wall area
- Wall area from the formula above, expressed in sqft before metric conversion. All standard CMUs share the 16 × 8 in face module (1.125 blocks per sq ft); half blocks cover half that face. The mortar figure uses the published planning rate of about 37 standard blocks per 80 lb bag — confirm with your mortar brand.
- Mortar bags (80 lb, approx.)
- Mortar bags (80 lb, approx.) from the formula above. All standard CMUs share the 16 × 8 in face module (1.125 blocks per sq ft); half blocks cover half that face. The mortar figure uses the published planning rate of about 37 standard blocks per 80 lb bag — confirm with your mortar brand.
Frequently asked questions
Standard 8 × 8 × 16 in blocks lay up at 1.125 blocks per sq ft, because each block plus its mortar joint covers a 16 × 8 in module.
160 sq ft × 1.125 = 180 blocks before waste; 198 with the default 10% waste allowance.
A common planning rate is one 80 lb bag of mortar per ~37 standard blocks (three bags per 100 sq ft of wall). Brand yields vary — check the bag.
Deduct large openings if you like, but corners, cuts and breakage usually consume the difference. Keep waste at 10% and do not deduct small windows.
This tool counts blocks and mortar only. Vertically reinforced or grouted cores need separate grout volume: roughly 0.5 cu ft per standard block core filled.