Inputs
Example data table
| Scenario | Wall length (m) | Cap size (L×W×T) | Joint (m) | Overhang (m) | Waste | Caps needed |
|---|---|---|---|---|---|---|
| Raised bed perimeter | 10.0 | 0.60 × 0.25 × 0.05 | 0.008 | 0.02 | 7% | 18 |
| Long boundary wall top | 22.0 | 0.50 × 0.30 × 0.06 | 0.010 | 0.03 | 10% | 49 |
| L-shaped garden wall | 14.0 | 0.60 × 0.25 × 0.05 | 0.008 | 0.02 | 7% | 27 (incl. corners) |
Formula used
- Piece step length: step = cap_length + joint_gap
- Base caps: base_qty = round_method(wall_length ÷ step)
- Corner allowance: corner_allow = corners × extra_pieces_per_corner
- Caps with waste: qty = ceil((base_qty + corner_allow) × (1 + waste%))
- Installed width: installed_width = cap_width + 2 × overhang
- Coverage area: area = wall_length × installed_width
- Mortar bed volume: bed = wall_length × cap_width × bed_thickness
- Joint volume: joints = (base_qty − 1) × joint_gap × cap_width × cap_thickness
- Total mortar: mortar_total = bed + joints
- Cost estimate: total_cost = (qty × price_per_cap) + mortar_cost
How to use this calculator
- Select a unit system and keep all inputs consistent.
- Enter the full wall length that will receive caps.
- Enter cap dimensions and a joint gap if using mortar joints.
- Add overhang to reflect how far caps extend past the wall.
- Set a waste percentage for breakage and cutting.
- If you have corners, add the corner count and extra pieces.
- Enter pricing and mortar cost to estimate the project budget.
- Press Calculate to see results above, then export if needed.
Article
Selecting cap size for garden performance
Wall caps protect masonry and timber edges from splashback, irrigation overspray, and freeze–thaw stress. A wider cap with modest overhang helps shed water away from the wall face, reducing staining and moss growth. Match cap thickness to handling needs and the wall’s rigidity; heavier caps resist movement but require stronger bedding and safer lifting practices.
How quantity is estimated on real projects
This calculator uses the effective step length (cap length plus joint gap) to convert a continuous wall run into discrete pieces. Rounding up is recommended because small layout changes, cuts near ends, and alignment at gates often consume additional pieces. Corner allowances are separated from the main run so you can budget for miters, return pieces, or dedicated corner units.
Mortar bed and joint planning for durability
The mortar estimate combines a uniform bedding layer beneath the cap and a simplified joint volume between pieces. Bedding thickness influences leveling tolerance and bond strength; too thin can create hollow spots, while too thick can shrink and crack. Keep joints consistent to limit rocking and water pathways, and use compatible mortar for the cap material and climate.
Cost and weight checks before you buy
Material cost is calculated from caps with waste plus a mortar cost estimate. Treat costs as planning values; supplier variation, delivery fees, and specialty corner pieces may change totals. The weight estimate helps confirm if the caps are manageable for one person or if you should plan for two-person handling, a cart, or staged deliveries.
Example data for a typical raised bed wall
Example inputs: wall length 10.0 m, cap 0.60 m long × 0.25 m wide × 0.05 m thick, joint gap 0.008 m, overhang 0.02 m, bed thickness 0.01 m, waste 7%, corners 0, price per cap 4.50, mortar cost per m³ 90.
Example outputs: base caps 17, caps with waste 18, coverage area 2.90 m², mortar about 0.026 m³ (≈26 L), and total cost about 83.00 (currency units). Use your own prices and allowances to refine purchasing quantities.
FAQs
1) Should I always round up the cap quantity?
Yes. Rounding up reduces the risk of shortages caused by cuts, chipped pieces, or end adjustments. It is usually cheaper than pausing work to source matching caps later.
2) What waste percentage is reasonable for caps?
For straight runs, 5–10% is common. If you have many corners, curves, or frequent cuts, increase waste to 10–15% depending on your experience and material fragility.
3) How do I set joint gap for dry-laid caps?
Use a joint gap near zero for tight dry placement. If you use spacers or want drainage gaps, enter that spacing so the step length reflects the true layout.
4) Does overhang change the number of caps needed?
No. Overhang affects coverage width and area, not the count. It is included so you can plan the cap footprint and confirm it sheds water beyond the wall face.
5) How accurate is the mortar volume estimate?
It is a planning estimate based on uniform bedding and simplified joint volumes. Surface irregularities, buttering methods, and tooling can change usage. Add a small buffer if you are unsure.
6) How should I handle corners in the calculator?
Enter the number of corners and the extra pieces you expect per corner. For mitered corners, one extra piece per corner is common. For special corner units, use your supplier’s guidance.
7) Can I use this for curved garden walls?
Yes, as a first estimate. Curves usually increase cutting and waste. Measure the curve length carefully, add more waste, and consider shorter cap lengths that follow the radius more easily.