Retaining Wall Calculator
Calculate concrete blocks, mortar, footing, and drainage for retaining walls. Stability check against overturning. South African pricing for blockwork, brick, gabion, and timber sleeper walls.
Quick Calculator Get a fast estimate
m
m
mm
Wall face area
12 m²
Blocks required (+10% waste)
165 blocks
Wall volume
2,76 m³
Footing concrete (25kg bags)
116
Estimated total cost
R 10 200
Cost per m² face area
R 850/m²
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How to Use the Retaining Wall Calculator
Enter wall dimensions, select the wall type, and specify the wall thickness. The calculator gives block quantities, concrete footing volumes, and an estimated cost using 2024 South African contractor rates.
The Extended Calculator adds drainage system quantities and a simplified overturning stability check. The Professional Calculator covers RC cantilever design checks, surcharge loading, and a comparison of wall type options.
Need more detail?
Extended Calculator More options, charts, and scenario comparison
m
m
mm
Material quantities
12 m² face area
Concrete blocks (390mm)
165 blocks
Wall volume
2,76 m³
Mortar (bags 40kg)
6 bags
Footing concrete (m³)
2,88 m³
Retaining Wall Design Basics
Face area = length × height (m²)
Blocks (390mm): area × 12.5 × 1.1 (wastage)
Footing volume = length × 0.5m × (2.5 × wall thickness)
Active soil pressure: Ka = tan²(45° − φ/2)
Lateral force: H = 0.5 × Ka × γ × h²
Factor of safety (overturning) must be ≥ 1.5
Retaining Wall Type Guide
| Type | Max height | Cost/m² | Engineer required? |
|---|---|---|---|
| Gravity concrete | 1.0 m | R600–R800 | No (<1.5m) |
| Concrete blockwork | 1.5 m | R750–R950 | Above 1.5m |
| Cantilever RC | 4.0 m | R1,000–R1,600 | Yes |
| Gabion baskets | 3.0 m | R650–R900 | Above 1.5m |
| Timber sleepers | 1.2 m | R550–R750 | No (<1.2m) |
Need full precision?
Professional Calculator Complete parameters, sensitivity analysis, and detailed breakdown
m
mm
mm
mm
°
kN/m³
Cantilever RC wall check
FOS = 6,23 (OK)
Active pressure Ka
0,333
Lateral force
12 kN/m
Overturning moment
8 kN·m/m
Total vertical load
71,16 kN/m
Bearing pressure
50,8 kPa
This is an indicative check only. Retaining walls >1.5m require a registered professional engineer's design certificate under SANS 10160. Clay soils require specialist geotechnical assessment.
Frequently Asked Questions
390mm blocks: 12.5 per m². Wall 10m × 1.5m = 15m² × 12.5 × 1.1 = 206 blocks. Plus 10 bags mortar (40kg). Add footings: 10m × 0.5m × 0.6m = 3m³ concrete ≈ 120 × 25kg bags. Always get blocks from the same production batch for colour matching.
Absolutely. Hydrostatic pressure can collapse walls. Install: 300mm drainage gravel behind wall, geotextile filter fabric to prevent soil migration, 110mm slotted pipe at footing level, and weep holes through wall every 1.5–2m. Critical in clay soils (Johannesburg, Pretoria highveld).
SANS 10160: walls >1.5m require PE design certificate. Municipal bylaws typically require plan approval for walls >1m. Clay soils always need a geotechnical report. Non-compliant walls can cause injury, insurance claims rejection, and boundary disputes.
Up to 600mm: timber sleepers or dry-stacked segmental blocks. 600mm–1.2m: mortared blockwork with footing. Over 1.2m: RC blockwork or cantilever wall by engineer. In Cape Town's sandy soils, gabion walls work well. Gauteng clay needs extra drainage and deeper footings.
Rule of thumb: base width = 0.4–0.6× wall height for gravity walls. For 1m wall: 400–600mm. Standard blockwork: 230mm for walls up to 1m, double-leaf for taller. Cantilever RC: stem 150mm + 20mm per m of height. Increase 25% for clay soils.