| Scenario | Wall (L × H) | Block size (face) | Waste | Estimated blocks | Estimated caps |
|---|---|---|---|---|---|
| Raised garden bed | 6 m × 0.6 m | 30 cm × 15 cm | 5% | ~ 88 | ~ 21 |
| Terraced slope | 10 m × 1.0 m | 30 cm × 15 cm | 7% | ~ 252 | ~ 36 |
| Decorative edging (low wall) | 12 m × 0.45 m | 20 cm × 10 cm | 8% | ~ 324 | ~ 60 |
- Total wall height:
H_total = H_above + H_embed - Courses:
Courses = ceil(H_total / BlockFaceHeight) - Blocks per course:
Blocks/course = ceil(WallLength / BlockFaceLength) - Total blocks:
TotalBlocks = ceil(Courses × Blocks/course × (1 + Waste%)) - Cap blocks:
Caps = ceil(ceil(WallLength / CapLength) × (1 + Waste%)) - Trench excavation:
V_trench = WallLength × BaseWidth × (BaseThickness + Embedment) - Base gravel:
V_base = WallLength × BaseWidth × BaseThickness - Drainage gravel:
V_drain = WallLength × DrainWidth × H_total - Backfill soil:
V_soil = max(0, WallLength × BackfillDepth × H_total − V_drain) - Geogrid layers (rule-of-thumb):
Layers = floor((H_total − FirstLayer)/Spacing) + 1 - Geogrid area:
A_grid = WallLength × GridLength × Layers × (1 + Waste%)
- Choose units first, then enter wall length and height.
- Enter block face size from your supplier’s spec sheet.
- Set embedment and base based on your site and climate.
- Adjust drainage zone width and backfill depth as planned.
- Enable geogrid if the wall is tall or soils are weak.
- Press Calculate, review totals, then export CSV/PDF.
Accurate Dimensions Drive Reliable Counts
Measure wall length along the finished curve, not the excavation line. Use the block face length and face height from the supplier sheet, because nominal sizes vary by brand. The calculator rounds up to full courses and full blocks per course, then applies a waste allowance for cuts, breakage, and future repairs.
Embedment and Base Improve Stability
Retaining walls perform better when the first course is partially buried and supported on compacted base gravel. Embedment increases total wall height, which increases the number of courses and blocks. Base thickness and base width also affect trench excavation volume and the quantity of compacted gravel you should order. A wider base helps leveling, while a well-compacted layer reduces settlement that can telegraph into the face.
Drainage Materials Reduce Water Pressure
Water is the common cause of wall movement. A drainage gravel zone behind the blocks creates a free-draining path to the perforated pipe at the base. The calculator estimates drainage gravel volume, soil backfill volume, pipe length with allowance, and landscape fabric coverage to separate soil from clean gravel. Keep outlets clear, provide fall to daylight where possible, and avoid clogging the gravel with fines during backfill.
Geogrid Options for Taller Garden Walls
For higher walls or weaker soils, reinforcement can be added with geogrid layers extending into the slope. When enabled, the calculator estimates layer count from the first layer height and vertical spacing, then converts total grid area into roll quantities using your roll width and roll length settings. This output supports budgeting and ordering, but it does not replace engineering checks for slope geometry, surcharge loads, or property setbacks.
Ordering and Site Logistics
Round up deliveries to full pallets or bundles when possible, and stage materials close to the work zone to reduce handling time. Compare calculated excavation to disposal or reuse plans, and verify access for wheelbarrows or small equipment. After layout, re-run the calculator with final dimensions and a refined waste percentage. Small changes in height can add an entire course, so confirm grades before ordering and schedule extra base material for touch-ups.
1) Why does the calculator round up block quantities?
Walls are built in complete courses, and each course needs whole blocks. Rounding up prevents shortages caused by partial coverage, end cuts, and small measurement changes. Use the waste percentage to match your cutting complexity.
2) Should I include the buried portion of the wall height?
Yes. Embedment adds courses and affects both block counts and drainage volumes. Enter the above-grade height separately and add embedment as its own input so totals reflect the full build height.
3) What waste percentage is reasonable?
For straight runs with few cuts, 5–7% is typical. Curves, steps, and corners often need 8–12%. Increase waste if you expect breakage, mixed patterns, or if matching color lots is important.
4) How are gravel and soil volumes estimated?
Volumes are based on wall length, total height, base width, and the selected backfill and drainage zone widths. These are planning estimates; field conditions, over-excavation, and compaction can change actual quantities.
5) When should I enable geogrid reinforcement?
Enable it for taller walls, poor soils, steep slopes, or where extra stability is needed. The tool estimates layers and rolls for budgeting, but spacing and length should follow manufacturer guidance and local requirements.
6) Can I use the CSV or PDF for supplier quotes?
Yes. Exports summarize blocks, caps, gravel, pipe length, fabric, and optional geogrid. Treat them as an estimate, then confirm product coverage, pallet quantities, and delivery constraints with your supplier before ordering.