Calculator
Example data table
| Shape | Inputs | Depth | Waste | Density | Estimated volume | Estimated bags |
|---|---|---|---|---|---|---|
| Rectangle | 3.0 m × 1.5 m | 5 cm | 7% | 1600 kg/m³ | 0.241 m³ | 16 (25 kg bags) |
| Circle | 2.0 m diameter | 4 cm | 10% | 1550 kg/m³ | 0.138 m³ | 9 (25 kg bags) |
| Custom area | 80 ft² | 2 in | 8% | 100 lb/ft³ | 14.4 ft³ | 29 (0.5 ft³ bags) |
Formula used
- Rectangle: Area = Length × Width
- Circle: Area = π × (Diameter ÷ 2)²
- Custom: you enter measured area directly
- By weight: Bags = Mass ÷ Bag Weight
- By volume: Bags = Volume ÷ Bag Volume
- Order is rounded up to whole bags.
How to use this calculator
- Select a unit system and an area shape.
- Enter dimensions or a measured custom area.
- Choose your top layer depth and waste allowance.
- Enter bulk density from your supplier, if available.
- Select bag sizing method and fill bag details.
- Optional: add pricing to estimate your budget.
- Click Calculate to view results above.
- Use CSV or PDF buttons to save the report.
Purpose of a Pebble Top Layer
A pebble top layer protects soil from splash, crusting, and erosion while keeping beds tidy. It reduces evaporation on hot days, moderates surface temperature swings, and improves appearance around plants and irrigation lines. When combined with drip irrigation, it can help keep foliage drier by limiting muddy rebound during watering.
Choosing Depth and Stone Size
Depth and stone size work together. Small pebbles lock in place and create a smooth look, but they can migrate into soil if the layer is thin or the bed is frequently cultivated. Larger stone drains faster and resists displacement, yet it needs more depth for full coverage and can feel uneven underfoot. For ornamental beds, 3–6 cm commonly balances coverage and maintenance; for light‑use paths, 5–8 cm is typical.
Coverage, Waste, and Ordering Strategy
Measure the footprint carefully, then apply a waste allowance for trimming, uneven ground, and settling. A 5–10% allowance suits straight beds with edging; complex curves, steep slopes, and thick fabric overlaps may require 10–15%. Order whole bags or round bulk deliveries upward to avoid mid‑project shortages and visible color differences between batches. The calculator’s bag rounding supports practical purchasing.
Density, Weight, and Handling Considerations
Bulk density converts volume into weight for transport planning. Decorative pebbles often range from 1400–1700 kg/m³ when dry; moisture and fines increase weight and reduce usable void space. Use the weight output to confirm vehicle payload, wheelbarrow capacity, and safe lifting limits. If buying in bags, compare labeled bag weight to your calculated mass to validate the density assumption.
Installation and Long‑Term Performance
Prepare a firm, level surface and remove existing weeds. A permeable landscape fabric can separate soil from stone, but keep it flat so water infiltrates instead of channeling. Spread pebbles evenly, rake to thickness, and keep stone away from plant crowns to reduce rot risk. After the first watering, expect settling; top up thin spots and record depth for future touch‑ups.
FAQs
Most beds look clean at 3–6 cm depth. Use the lower end for small pebbles and tight planting, and the higher end for larger stone or areas exposed to runoff and foot traffic.
A permeable fabric can slow weeds and keep stone from mixing into soil. Overlap seams and pin it flat so water infiltrates. Avoid sealing the surface with plastic, which can trap water and harm roots.
Density converts volume into weight, helping you plan transport, lifting, and bulk pricing. If you do not know it, start with a typical value and compare the weight result with supplier bag labels.
Use 5–10% for straight beds with edging. Increase to 10–15% for curved borders, steep slopes, or uneven ground where trimming and spillage are higher.
Yes. Select the area shape and enter a path depth that matches use. Light paths often need 5–8 cm, while high‑traffic paths may need a thicker base layer beyond the decorative top layer.
Keep stone a few centimeters away from crowns and stems, especially for tender plants. Use edging to contain spread, and rake occasionally to maintain an even thickness without piling material against plants.