A quantity estimator, with explicit assumptions
All calculations use a consistent internal feet-and-inches representation and convert the displayed results to metric when selected. Decimal input is accepted for measured dimensions. Course counts, unit counts, caps, tubes, pallets and pipe rolls round upward with a small numerical tolerance to avoid floating-point errors at exact integer boundaries.
The model describes uniform rectangular sections and a constant reference arc for a curved wall. It does not model batter-dependent course radii, earth pressures, soil behavior, foundation design or excavation overlap.
Formula reference
Use compatible length units before multiplying. Base and drainage outputs include the entered stone allowance. Core-fill volume uses net installed units, excluding spare waste units.
| Output | Formula / treatment |
|---|---|
| Wall units | ceil(Σ(ceil(L / module L) × (ceil(H / module H) + buried courses)) × (1 + waste/100)) |
| Caps | ceil(Σ ceil(section L / cap coverage) × (1 + waste/100)) |
| Base stone | L × (block depth + extra width) × base depth / 27, then stone allowance |
| Drainage stone | Σ L × width × max(total courses × course height − soil cap, 0) / 27 + net unit core fill / 27; then stone allowance |
| Pipe | Total wall run + entered outlet allowance; rolls round up |
| Fabric | Σ L × (constructed height + drainage width) × (1 + overlap/100) |
| Adhesive | ceil(L × bead count × (1 + waste/100) / entered tube coverage) |
| Geogrid | L × entered plan depth × entered plan layers × (1 + waste/100) |
| Materials | Σ displayed quantity × entered price |
| Labor and tax | Exposed face area × labor rate; tax on materials plus delivery |
Exact measurement conversions
Changing the unit system preserves the same project and physical costs. A currency change only changes the label; it does not convert prices through an exchange rate.
| From | To |
|---|---|
| 1 ft | 0.3048 m |
| 1 in | 25.4 mm |
| 1 ft² | 0.09290304 m² |
| 1 ft³ | 0.028316846592 m³ |
| 1 yd³ | 0.764554857984 m³ |
| 1 US short ton | 907.18474 kg |
| 1 metric tonne | 1,000 kg |
Purchasing and geometry limits
Line-item costs use individual units and geometric stone quantities, not rounded full-pallet or full-truck invoice quantities. Delivery is a separate input, and tax is a simplified budgeting assumption. Specialty blocks, fittings, footings, mortar, grout, steel, anchors, permits, equipment and site work need separate schedules.
A one-course buried default and the entered base and drainage sizes are starting assumptions. They are not universal design rules. The optional geogrid input is quantity-only and never decides whether reinforcement is required.
References and scope
Arithmetic and worked examples are explained on our methodology page. These manufacturer references provide product-specific context, not approval of a generic wall. Accessed October 1, 2026.
- Allan Block: residential basic installation
- Allan Block: reinforcement installation
- Allan Block: residential retaining wall manual
Read the estimating and engineering limits, or send a correction.