How deep should gravel be?

Paths: 3-5cm. Drives: 5-7cm. Decorative: 3-4cm. Deeper is more stable but uses more material.

How much does gravel weigh?

Approximately 1.5 tonnes per cubic metre for most gravels. Slate chips are slightly lighter.

A bulk (or "tonne") bag holds roughly 0.5m³ and weighs about 850kg of gravel, despite the nickname. This calculator orders bulk bags at 850kg each, so it allows for the fact that one bag is not a full tonne. At 50mm depth an 850kg bag covers roughly 10-12m².

Do I need a membrane under gravel?

Yes, always lay a weed membrane before gravel on paths and drives. It prevents weeds growing through and stops gravel mixing into the sub-soil.

What size gravel is best for a path?

10-20mm is the most popular for paths and drives. Smaller (6-10mm) works for decorative beds. Larger gravel (20-40mm) is harder to walk on and shifts more.

GardenCalcs

Gravel Calculator — How Much Gravel

Work out gravel quantities in tonnes or bulk bags for drives and paths.

Length

Length of the area to be gravelled, measured along the longest side.

Width

Width of the area. For an irregular shape, split it into rectangles and add the results.

Depth

Finished gravel depth: 3-4cm for decorative beds, 5cm for paths, 5-7cm for drives.

Gravel TypeSets the bulk density used to convert volume to weight (1.4-1.6 t/m³).

Price per Bulk Bag (optional)

Price of one 850kg bulk bag, to estimate total cost. Leave at 0 to skip costing.

Include 10% wastage

Adds a margin for compaction, levelling and spillage so you do not run short. Adjust the percentage under Advanced Options.

How We Calculate This

Volume = Length × Width × Depth (depth converted from cm to metres). Weight = Volume × Density, where decorative gravel is about 1.5 t/m³, pea gravel 1.6, limestone 1.5 and slate chips 1.4. Bulk bags are ordered at 850kg each (a typical UK "tonne" bag), and the same weight is also shown as 25kg bags for smaller top-up jobs.

Frequently Asked Questions

Related Calculators

Paving Slab Calculator

Calculate how many paving slabs you need for a patio or path.

Patio Area Calculator

Calculate patio area and materials for rectangular or L-shaped patios.

Stepping Stone Calculator

Work out stepping stone quantities and spacing for garden paths.

Block Paving Calculator

Calculate block paving quantities with wastage allowance.

Sand Sub-Base Calculator

Work out sharp sand and sub-base aggregate for paving foundations.

Last updated: February 2026

All calculations are estimates based on standard gardening guidelines. Results may vary with soil conditions, climate, and plant varieties.