CalcLandscape Rock Calculator
Last updated: 2026-05-07
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| area_length (m) | area_width (m) | depth_cm (cm) | rock_type |
|---|---|---|---|
| 3 m | 2 m | 8 cm | 1 |
| 5 m | 3 m | 8 cm | 1 |
| 6 m | 4 m | 8 cm | 1 |
| 8 m | 5 m | 10 cm | 1 |
| 10 m | 8 m | 10 cm | 2 |
What is the Landscape Rock Calculator?
Landscape rocks and decorative gravel are sold by weight (tonnes) or volume (m³) depending on the supplier. Ordering by eye always leads to either bare patches or a leftover pile. This calculator converts your area dimensions and desired depth into the exact tonnes or cubic metres to order, using the density of the specific rock type you choose.
You may also find the Mulch Calculator, Paver Calculator, and Sod & Turf Calculator useful.
Who Uses This Calculator?
This tool is used by homeowners landscaping garden beds, landscapers quoting rock supply jobs, and garden centres estimating delivery volumes.
How to Use the Landscape Rock Calculator
- Enter your Area length.
- Enter your Area width.
- Enter your Rock depth.
- Enter your Rock type.
- Click Calculate to see your results instantly.
Formula
The calculator uses the following formula:
Area = Length × Width; Volume = area × (depth ÷ 100); Tonnes = volume × rock_density
Worked Example
A 8 m × 3 m garden bed with 80 mm depth of river pebbles (density 1.5 t/m³) requires 1.92 m³ of rock, or approximately 2.9 tonnes to order.
Step-by-Step Calculation
- Area: 6 m × 4 m = 24 m²
- Depth in metres: 8 cm ÷ 100 = 0.08 m
- Volume: 24 × 0.08 = 1.92 m³
- Crushed granite density ≈ 1.6 t/m³: 1.92 × 1.6 = 3.07 tonnes
Common Mistakes to Avoid
- Underestimating depth — decorative rock needs minimum 5-8 cm to suppress weeds
- Forgetting to install landscape fabric under the rock
- Using volume (m³) pricing when ordering by weight (tonnes) — convert correctly
Frequently Asked Questions
For weed suppression: 75–100 mm minimum. For decorative effect: 50–75 mm. For pathways: 50 mm. For drainage: 150–200 mm. Deeper layers are more effective at blocking weeds but require significantly more material.
Crushed granite: 1.6 t/m³. River pebbles: 1.45–1.5 t/m³. Basalt: 1.6–1.7 t/m³. Decomposed granite (DG): 1.4 t/m³. Limestone: 1.5–1.6 t/m³. Use the correct density for your material to get an accurate weight.
Yes — install woven geofabric before laying rock. It allows water through while blocking weed growth. Avoid plastic sheeting which prevents drainage and kills plant roots. Pin the fabric at edges before covering with rock.
Volume (m³) × density (t/m³) = weight (tonnes). For river pebbles at 1.5 t/m³: 2 m³ × 1.5 = 3 tonnes. Suppliers often quote in one unit — ask for both so you can compare quotes from different suppliers.
One tonne of river pebbles covers approximately 10–12 m² at 50 mm depth, or 5–6 m² at 100 mm depth. For crushed granite, one tonne covers 8–10 m² at 50 mm. Always calculate volume first, then convert to tonnes.