Retaining Wall Calculator — Blocks, Sleepers & Gabions

Standard concrete blocks (440 x 215mm face) require approximately 10 blocks per m² of wall face when laid with 10mm mortar joints. For a single-skin wall 5m long x 1m high (5 m²), you would need 50 blocks plus 10% wastage = 55 blocks. Note this counts one block thickness only — an earth-retaining wall often needs a double-skin (or filled-cavity) section, which doubles the block count. Always follow the structural design for your wall. This retaining wall material calculator covers blocks, sleepers and gabions.

Yes — all retaining walls need a concrete foundation (footing). The foundation should be at least 150mm deep and wider than the wall. For concrete block walls, the foundation should be at least 300mm wide. Pour the concrete into a trench dug below topsoil level on firm, undisturbed ground. The Type 1 sub-base can be used under sleeper walls — see our Type 1 Sub-Base Calculator.

In England and Wales, walls up to 1 metre high adjacent to a highway, or 2 metres high elsewhere, generally do not require planning permission under permitted development rights (GPDO 2015, Schedule 2, Part 2, Class A). Note that case law has held that earth-retaining walls often fall outside these enclosure rights, so check with your local planning authority. As a rule of thumb, any wall retaining more than about 1m–1.2m of soil should be designed by a structural engineer to BS 8002:2015 / Eurocode 7 — this is good practice, not a fixed statutory trigger. Building Regulations may still apply. For fencing instead, see our Fence Post Spacing Calculator.

Yes — drainage behind a retaining wall is critical to prevent water pressure building up and pushing the wall over. Install a French drain along the back of the wall — use our French Drain Calculator for gravel and pipe quantities. Weep holes at the base of blockwork walls also help relieve water pressure. Calculate the pipe gradient with our Drainage Fall Calculator.

Gabion walls use wire mesh baskets filled with stone or aggregate. They are excellent for retaining walls as they are flexible, free-draining and very strong. The most common UK basket is 1m long × 0.5m high × 1m deep (a half-metre-high course basket); 1m × 1m × 1m cages are also widely used. They do not need mortar and can be stacked to create walls up to 3-4 metres high with proper engineering. Fill the raised bed behind with soil — use our Raised Bed Soil Calculator or Topsoil Calculator.