How this calculator works for metric users
The calculation is the same as the imperial version, just in different units:
- Length and width in metres
- Depth in centimetres (or metres if you prefer)
- Volume output in cubic metres (m³)
- Weight output in kilograms and metric tonnes (1 tonne = 1,000 kg)
UK material naming
UK and EU stone names differ from US grades. The closest matches:
- MOT Type 1 ≈ US ABC / Crusher Run (driveway base)
- 10 mm gravel ≈ US pea gravel
- 20 mm gravel ≈ US #57 crushed stone
- 40 mm gravel ≈ US #4 crushed stone
Density values used here (kg/m³): pea gravel ~1,450 kg/m³, #57 ~1,630 kg/m³, ABC/MOT Type 1 ~1,600 kg/m³, river rock ~1,510 kg/m³, lava rock ~890 kg/m³. These are derived from the US lb/yd³ figures via the standard conversion (1 lb/yd³ ≈ 0.5933 kg/m³).
Recommended depth & material
| Use | Depth | Material | Notes |
|---|---|---|---|
| Decorative bed / ground cover | 50 – 75 mm | Pea gravel / 10 mm gravel | Over weed barrier. |
| Path / walkway | 50 – 75 mm | Decomposed granite / 10 mm gravel | Over compacted base. |
| Patio / paver base | 100 mm + 25 mm sand | MOT Type 1 base, sharp sand | Two-layer build. |
| Light driveway | 100 mm base + 50 mm top = 150 mm | MOT Type 1 base, 20 mm gravel top | Standard UK residential drive. |
| Heavy driveway / RV | 150 mm base + 75 mm top = 225 mm | MOT Type 1 + 40 mm sub-base, 20 mm top | Add geotextile. |
| Drainage trench | 300 mm | 20 mm washed gravel | Around perforated pipe. |
How to measure for a metric gravel order
UK and EU suppliers sell gravel by the tonne (1,000 kg) or by the cubic metre. Both numbers are on the calculator output.
- Measure length and width in metres. Use a tape measure marked in cm and metres. For long runs, a measuring wheel is faster.
- Pick depth in centimetres. Common UK depths: 50 mm (decorative), 75 mm (paths), 100 mm (driveways and patios), 150 mm (heavy use). The presets handle these.
- Choose material. Pick the closest US equivalent in the picker. Your UK supplier will know what "20 mm gravel" or "MOT Type 1" means even if the calculator names it differently.
- Read tonnes for ordering. Most UK suppliers quote in tonnes. The calculator shows tonnes directly. For bulk-bag suppliers, check the bag size (typically 0.5 m³ or 850 kg).
- Add 10% buffer. Same advice in any unit: 10% covers compaction, spillage, and small measurement errors.
- Confirm bag vs loose-load pricing. UK suppliers offer both 'jumbo bags' (~850 kg) and tipper-loaded loose. Loose is cheaper per tonne; bags are more convenient for tight access.
Worked example: 5 m × 8 m driveway, 100 mm of MOT Type 1
A typical UK residential driveway: 5 m × 8 m = 40 m² at 100 mm depth.
- Volume: 40 × 0.1 = 4.0 m³
- Weight: 4.0 × 1,600 = 6,400 kg = 6.4 tonnes
- With 10% buffer: ~7 tonnes of MOT Type 1.
- Cost: at £40/tonne delivered (typical UK price for MOT Type 1), ~£280 in stone, plus a £40–£80 delivery fee.
- Or in bulk bags: ~7-8 jumbo bags at £55-£70 each = £400-£560 — convenient but ~50% more expensive than tipper-loaded.
Same area at 150 mm (heavier driveway use): volume rises to 6.0 m³ → ~9.6 tonnes → roughly £400 in stone.