Retaining Wall Calculator

Block count = (Wall Length / Block Length) x (Wall Height / Block Height), plus a waste factor for cuts. Standard UK dense concrete blocks are 440 x 215mm on the face (≈10 blocks/m² with 10mm joints).

Mortar is calibrated to manufacturer coverage, not just joint geometry — a 25kg bag (~0.012 m³) lays about 12 100mm blocks with a 10mm joint. Because the bed and perpend joints run the full block depth, mortar scales with depth, so a 215mm-deep wall needs roughly 1.8 bags/m², about double a 100mm block.

Drainage includes a 150mm gravel layer behind the wall, perforated pipe at the base, and geotextile membrane to stop soil clogging the drainage. Backfill is calculated as a 300mm depth behind the wall face.