GardenCalcs.uk
Gravel Calculator — How Much Gravel
Work out gravel quantities in tonnes or bulk bags for drives and paths.
Length of the area to be gravelled, measured along the longest side.
Width of the area. For an irregular shape, split it into rectangles and add the results.
Finished gravel depth: 3-4cm for decorative beds, 5cm for paths, 5-7cm for drives.
Sets the bulk density used to convert volume to weight (1.4-1.6 t/m³).
Price of one 850kg bulk bag, to estimate total cost. Leave at 0 to skip costing.
Adds a margin for compaction, levelling and spillage so you do not run short. Adjust the percentage under Advanced Options.
Extra material to account for waste and spillage
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
Paths: 3-5cm. Drives: 5-7cm. Decorative: 3-4cm. Deeper is more stable but uses more material.
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.
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.
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.
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Last updated: February 2026
All calculations are estimates based on standard gardening guidelines. Results may vary with soil conditions, climate, and plant varieties.