About This Calculator
This calculator estimates the number of concrete blocks needed for building walls. It accounts for different block sizes, mortar joints, and wastage.
Concrete blocks are faster to lay than bricks and provide excellent thermal and acoustic insulation. They're commonly used for internal walls, partitions, and as the inner leaf of cavity walls.
Block Types
- Standard Hollow (440 × 215 × 100mm)
Most common block for internal walls. Lightweight with hollow cores. ~10 blocks/m² - Paint Grade Solid (440 × 140 × 100mm)
Dense solid block with smooth finish, ready for direct painting. ~13 blocks/m² - Large Format (610 × 270 × 100mm)
Bigger blocks for faster construction. ~6 blocks/m²
Tips for Ordering
- • Add 5% for wastage and breakages
- • Standard pack sizes are usually 72 or 90 blocks
- • Consider delivery access - blocks are heavy!
- • Store blocks off the ground and cover if raining
Block vs Brick
Blocks are typically 4× larger than bricks, meaning faster construction and lower labour costs. They're ideal for internal walls where appearance isn't critical.
Ready to Calculate?
Enter your wall dimensions, select block type, and get an instant estimate.
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NAIBC / IRC codes
References & Sources
Standards Cited
- ASTM C90 — Standard Specification for Loadbearing Concrete Masonry Units
Defines standard CMU dimensions (8x8x16 in, 4x8x16 in, 12x8x16 in) and tolerances used in the calculator - TMS 402/602 — Building Code Requirements and Specification for Masonry Structures
Design rules for CMU blockwork including mortar joint specifications and structural requirements
Formulas Used
- Blocks per m2:
blocksPerM2 = 1 / ((blockLength + mortarJoint) x (blockHeight + mortarJoint))
Source: ASTM C90 / TMS 402/602 — Standard 440x215mm block with 10mm joints gives approximately 10 blocks per m2 - Total blocks:
totalBlocks = ceil(netWallArea x blocksPerM2 x (1 + wastage/100))
Source: Standard quantity surveying method
Key Assumptions
- Standard CMU: 406 x 203 x 203mm (8x8x16 in); half block: 406 x 203 x 102mm; large: 406 x 203 x 305mm — ASTM C90
- Default mortar joint width: 10mm (3/8 in) — TMS 402/602
- Typical wastage allowance of 5% for cutting and breakage — Industry standard practice