Concrete Block Calculator
Calculate how many concrete blocks (CMU) you need for any retaining wall, garden wall or structural blockwork. Get block count, mortar and cost estimate instantly. Metric and imperial.
🔨 Concrete Block Calculator
📐 How It Works
Block count is wall area divided by the face area of each block including mortar joints. Standard 390×190mm blocks with 10mm mortar joints cover 0.08 m² face area giving approximately 12.5 blocks per m² of wall face.
📋 Worked Example
Garden wall 6m × 1.2m using standard 390×190mm blocks: Area = 7.2 m². Blocks = 7.2 × 12.5 × 1.10 = 99 blocks. Mortar: ~6 bags of 30kg premix.
❓ Frequently Asked Questions
Standard 390×190mm blocks with 10mm mortar joints: approximately 12.5 blocks/m². 400×200mm blocks: approximately 11.4/m². Always add 10% for cuts and waste, particularly around corners and openings.
Hollow blocks have one or two cores and are lighter and cheaper. They can be filled with concrete and rebar for additional strength. Solid blocks are heavier and stronger but more expensive. Use hollow blocks for most garden and retaining walls; solid blocks where fire rating or structural strength is critical.
Retaining walls over 600mm high should be engineered and typically require vertical rebar in filled cores and horizontal reinforcement in mortar joints. Always consult a structural engineer for retaining walls — poor retaining wall design is a leading cause of construction failures.
Approximately 0.01–0.015 m³ of mortar per block including bed joints and perpend joints. A 30kg bag of premix mortar covers approximately 10–12 blocks. Pre-mixed mortar is more consistent than site-mixed for blockwork.