How much gravel do I need per m²?

The amount depends on depth. For decorative gravel at 40mm depth, you need approximately 70kg per m² (1.6 tonnes per m³ × 0.04m). For a gravel driveway at 75mm depth, you need approximately 130kg per m². Our calculator works this out automatically based on your chosen depth and aggregate type.

What is the difference between a bulk bag and a tonne?

A standard bulk bag (jumbo bag) holds approximately 850kg of aggregate, which is about 0.5m³. This means a bulk bag is NOT a tonne — you need roughly 1.2 bulk bags to make 1 tonne. Always check with your supplier as bag sizes can vary. Loose tipped deliveries are usually cheaper per tonne than bulk bags.

What depth of gravel do I need for a path?

For a garden path, 40-50mm of gravel over compacted sub-base is standard. For a gravel driveway, use 50-75mm of gravel over at least 150mm of compacted Type 1 MOT sub-base. Always use a geotextile membrane between layers to prevent mixing and weed growth.

How many 25kg bags per m²?

At 50mm depth with standard 20mm gravel: approximately 3.5 bags per m² (1,750 kg/m³ × 0.05m = 87.5 kg per m² ÷ 25 = 3.5 bags). At 25mm depth it halves to about 1.75 bags per m². 25kg bags are only economical for small areas — bulk bags or loose tipped are far cheaper for larger projects.

Do I need membrane under gravel?

Yes, always lay a geotextile weed membrane under gravel. This prevents weeds growing through, stops the gravel sinking into the soil, and keeps layers separated. Use heavy-duty landscape fabric (100g/m² minimum), overlapping joins by at least 150mm.

TradeCalcs

Aggregate Calculator — How Much Gravel, Sand or Stone Do I Need?

Calculate aggregate quantities in tonnes and bulk bags for paths, driveways and landscaping. UK standard sizes.

Area Length

Area Width

Aggregate Type

Depth

Include wastage allowance

Adds 10% for settlement and uneven sub-grade

Wastage Percentage

10% is standard for most aggregate projects

Include geotextile membrane

Weed membrane under aggregate (recommended)

Price Per Tonne (optional)

Price per tonne from your supplier

How We Calculate This

Our aggregate calculator converts your area and depth measurements into weight (tonnes and kg) and quantity (bulk bags and 25kg bags) using the specific density of each aggregate type.

The formula

Volume (m³) = Length × Width × Depth
Weight (kg) = Volume × Density
Bulk bags = Weight ÷ 850 kg
25kg bags = Weight ÷ 25 kg

Aggregate densities we use

20mm Gravel: 1,750 kg/m³
10mm Pea Gravel: 1,600 kg/m³
Slate Chippings: 1,500 kg/m³
Type 1 MOT: 1,800 kg/m³
Sharp Sand: 1,600 kg/m³
Building Sand: 1,500 kg/m³
Ballast: 1,800 kg/m³

These are average densities for loose material. Compacted Type 1 MOT will be denser. Always add 10% for wastage, settlement, and uneven sub-grades.

Frequently Asked Questions

Related Calculators

Topsoil Calculator

Calculate how many tonnes or bulk bags of topsoil you need.

Gravel Calculator

Work out gravel or aggregate quantities in tonnes and bulk bags.

Type 1 Sub-Base Calculator

Calculate Type 1 MOT sub-base quantities for driveways and paths.

Soakaway Sizing Calculator

Size a soakaway to UK BRE DG 365 standards for your roof area.

Fence Post Spacing Calculator

Calculate fence post quantities and optimal spacing.

Last updated: February 2026

All calculations are estimates. Verify with your supplier.