Retaining Wall Block Calculator
Calculate how many retaining wall blocks you need by wall length and height
Block Type
Most common residential retaining block
Wall Dimensions
10% recommended
Select a block type and enter your wall dimensions to see results
Tips & Notes
- •Walls over 4 feet tall typically require a permit and engineered batter (backward lean).
- •Add 10% extra blocks for cutting and waste.
- •Plan for drainage behind the wall: use 3/4" crushed stone and a perforated drain pipe.
- •Each course should step back slightly — most blocks are designed with a natural batter.
- •Cap blocks are typically the same length but shorter in height — order separately.
Recommended Products
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Materials & Supplies
Pro tips for retaining wall block
- ›Walls over 4 feet tall typically require a permit and engineered batter (backward lean).
- ›Add 10% extra blocks for cutting and waste.
- ›Plan for drainage behind the wall: use 3/4" crushed stone and a perforated drain pipe.
- ›Each course should step back slightly — most blocks are designed with a natural batter.
- ›Cap blocks are typically the same length but shorter in height — order separately.
Frequently asked questions
How many blocks do I need for a retaining wall?▾
Most segmental retaining wall blocks are 12" wide. A 20-foot wall that's 3 feet tall (4 courses for 8" tall blocks) needs 20 × 4 = 80 wall blocks plus 20 cap blocks. Add 10% for cuts and waste — order 88 wall blocks and 22 caps.
How tall can a retaining wall be without engineering?▾
Most jurisdictions allow walls up to 3–4 feet tall without an engineered design or permit. Walls over 4 feet typically require engineering, soil analysis, and inspection. Tiered shorter walls can avoid permits while retaining steeper slopes.
How much base gravel do I need behind a retaining wall?▾
Excavate 6"–8" below grade for compacted #57 crushed stone base, plus 12" of clean drainage stone behind the wall. For a 20'×3' wall, plan on 1.5–2 cubic yards of base gravel and 2–3 yards of drainage backfill.
Do I need a drain pipe behind a retaining wall?▾
Yes — for any wall over 2 feet tall. Install a 4" perforated drain pipe (drain tile) at the base, wrapped in filter fabric, sloped to daylight or to a drain. Without drainage, hydrostatic pressure builds up and pushes walls over.
How much do retaining wall blocks cost?▾
Standard concrete retaining wall blocks run $3–$8 each at retail. Cap blocks run $4–$10. Installed by a contractor, expect $20–$40 per face square foot for walls under 4 feet, or $40–$70/sq ft for engineered walls.