Gravel Calculator

Gravel Buying Guide

Depth Guide

The depth of gravel you need depends entirely on what it's for, and getting it wrong is the most common reason gravel jobs fail. Decorative garden paths and borders: 40–50 mm is enough for a clean look that contains the gravel without it sinking or moving much underfoot. Driveways for pedestrian-only use: 50 mm minimum. Driveways for cars and regular vehicle use: 75–100 mm of gravel on top of a properly compacted sub-base (essential — see the next section). Drainage layers around foundations or beneath patios: 100–150 mm to allow water to move freely. Under decking, to suppress weeds and aid drainage: 50 mm. For tree pits and around plants, mulching with gravel: 50–75 mm. The same surface area at different depths needs very different volumes: a 20 m² driveway at 50 mm needs 1 m³ of gravel; at 100 mm it needs 2 m³ — twice as much, twice the cost. Bulk density of gravel is roughly 1.5–1.8 tonnes per cubic metre, so 1 m³ weighs about 1.6 tonnes. A typical 850 kg bulk bag covers about 6 m² at 100 mm depth or 12 m² at 50 mm. The right gravel size also matters: 10–20 mm gravel is decorative and walkable; 20–40 mm is hardier for driveways; smaller pea gravel (5–10 mm) compacts well underfoot but spreads more easily; angular gravel locks together better than rounded stones, which is why crushed limestone or granite suits driveways better than rounded river pebbles.

Bulk Bags vs Mini Bags

Choosing between bulk bags and mini bags makes a meaningful difference in cost and effort for any reasonable-sized gravel job. Bulk bags (typically 0.85–1 tonne, sometimes called 'jumbo bags' or 'dumpy bags') are dramatically cheaper per kg than smaller bags — often around £40–70 each delivered, versus £4–6 per 25 kg mini bag, working out at roughly half the price per kg or less. For any area over about 20 m² (which needs more than one bulk bag), bulk bags are the obvious choice. Most suppliers deliver bulk bags with a HIAB lorry — a crane on the truck — that places the bag exactly where you want it, including in front gardens and side passages, provided there's reasonable access. Mini bags (typically 20–25 kg) suit small top-up jobs, tight access where a lorry can't reach, and projects where you'd rather not have a tonne of gravel sitting in your driveway for a weekend. They're also easier to handle alone — a 25 kg bag is heavy but moveable, while a 1-tonne bag needs the supplier's crane or a lot of shovelling. Consider where the bag will be delivered and whether you can spread it in a reasonable time: bulk bags left in driveways for weeks become eyesores and obstacles. Some suppliers also offer 'maxi bags' (around 400–500 kg) as a middle ground. For larger jobs (over 5 tonnes), loose tipping (the supplier dumps the gravel directly from the lorry onto your driveway) is the cheapest option of all, but you need to be able to take the delivery in one place and clear it quickly.

Sub-Base Matters

For driveways specifically, the sub-base under the gravel is more important than the gravel itself, and skipping it is the single biggest mistake DIY gravel driveways make. A compacted MOT Type 1 (a graded crushed stone aggregate) sub-base of 100–150 mm is essential — without it, vehicle tyres push the decorative gravel down into the underlying soft ground and create ruts within months, and the surface develops dips and potholes that are then very hard to fix without lifting everything and starting again. The MOT Type 1 binds together when compacted (with a plate compactor, hired by the day cheaply) and provides a hard, stable platform that distributes vehicle loads and prevents the surface gravel from working its way into the subsoil. The total dig depth for a proper gravel driveway is therefore 150–250 mm: 100–150 mm of compacted Type 1, then 75–100 mm of decorative gravel on top, sometimes with a weed-suppressant membrane between them. A driveway edging (concrete kerb, timber, or metal edging) is also worth adding to stop the gravel migrating onto pavements and lawns over time. For pedestrian-only paths and borders, a sub-base is less critical — a 50 mm layer of gravel on a weed membrane over reasonable ground does fine, though some compaction of the ground first helps. Plan the levels: you want the finished gravel surface to sit just below adjacent paving or thresholds, and to slope very slightly (say 1:80) away from buildings for drainage. Get these basics right and the gravel surface will last for many years; cut corners and you'll be redoing it within a season.

Safety and Regulations

Most structural and electrical DIY work in England and Wales must comply with Building Regulations and is notifiable to local Building Control. Work that is not notifiable (like-for-like replacements, cosmetic changes) can be done without notification. Notifiable work done without approval is technically illegal and can cause problems when selling the property. Electrical work in most rooms requires a Part P competent person or Building Control inspection. Gas work must always be performed by a