Estimate how many kg of pebbles or pea gravel you need from the area and depth, using typical pebble densities, with bag counts and kg per square metre.
Pebble Coverage Formula
The calculator estimates total order weight from area, layer depth and supplier bulk density. It can also estimate coverage area or layer depth from available total weight. An optional allowance reserves extra material; it is not a compaction model.
M = A × D × ρ × (1 + a/100)
A = M / [D × ρ × (1 + a/100)]
D = M / [A × ρ × (1 + a/100)]
- M = pebble mass required
- A = coverage area, from rectangle length × width, π × diameter² / 4, or a known area
- D = layer depth
- ρ = bulk density, including voids, in kg/m³; a = extra material allowance (%)
Select Pebble weight and bags needed, then enter the shape dimensions or known area and depth, and pick a pebble type or Custom bulk density. Select Calculate. Bag weight is optional.
Select Coverage from available weight to solve for area using total available weight, depth and bulk density.
Select Layer depth from available weight to solve for depth using total available weight, area and bulk density.
Inputs are converted to meters, kilograms and kg/m³, then results are converted to the selected unit. Changing an input unit converts the entered quantity. In inverse modes, any extra allowance is reserved from the available total weight.
Illustrative Pebble Application Rates
Application rate equals depth × bulk density before extra allowance. The following arithmetic examples assume a bulk density of 1,600–2,000 kg/m³; they are not universal product rates or construction recommendations. Use supplier coverage and the intended layer condition.
| Typical use | Approx. depth | Typical rate | Notes |
|---|---|---|---|
| Light decorative cover | 25 mm | 40 to 50 kg/m² | Illustrative arithmetic; verify the actual product. |
| General garden coverage | 40 mm | 64 to 80 kg/m² | Illustrative arithmetic; verify the actual product. |
| Deeper example layer | 50 mm | 80 to 100 kg/m² | Does not establish a suitable or load-bearing layer. |
Unit Conversion Reference
| Conversion | Value |
|---|---|
| 1 ft | 0.3048 m |
| 1 lb | 0.45359237 kg |
| 1 lb/ft² | 4.8824276 kg/m² |
| 1 kg/m² | 0.2048161 lb/ft² |
Example Calculations
Example 1: Find pebble mass
A 6 m × 2 m bed at 50 mm depth and an assumed bulk density of 1,500 kg/m³ has a base application rate of 75 kg/m². With 0% extra allowance, select the weight mode and enter those dimensions, depth and density.
You need about 900 kg of pebbles.
Example 2: Find coverage area
You have 500 kg total, a 50 mm layer and assumed bulk density of 1,500 kg/m³, with 0% allowance. Select coverage mode; the base application rate is 75 kg/m².
The pebbles cover about 6.67 m² under those assumptions.
FAQs
What application rate should you use for pebbles?
Use the supplier’s coverage or bulk density for the product and intended layer condition. For example, 75 kg/m² follows from 50 mm × 1,500 kg/m³ before extra allowance; it is not a universal garden rate.
How do I choose what to calculate?
Choose the named solve mode and complete its visible required inputs. The calculator does not infer the task from a blank input. Optional allowance may be blank for 0%; optional bag weight may be blank to omit bags.
Should you order extra pebbles?
Use an allowance suited to the actual product, ground and installation method. The calculator can add a chosen extra order percentage or reserve it from an available-material budget. This allowance does not simulate compaction or guarantee installed coverage.
