Gravel Calculator UK · metric

Tonnes, cubic metres, bulk bags and cost of gravel for drives, paths and borders. Metric units and £ costs, updated for 2026.

Last reviewed July 2026 · Free · Nothing you enter is stored

Length (metres) i

Width (metres) i

Depth (cm) i

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Planning estimate using standard formulas and 2026 UK average prices (excluding VAT) — confirm quantities with your supplier and get local quotes.

How this calculator works

Volume is area × depth in metres to give cubic metres. Decorative gravel weighs about 1.5 tonnes per m³, so tonnes = m³ × 1.5. Cost uses a UK average per-tonne rate; a standard bulk bag holds roughly 0.55 m³ (about 850 kg).

The waste allowance

Two different allowances are at work here and it is worth knowing which one applies. A decorative gravel surface is not compacted, so what you order is close to what ends up on the ground, and the only rounding needed is up to the next whole bulk bag or tonne because that is how suppliers sell. A sub-base is a different matter. MOT Type 1 arrives loose and full of voids, and once it is spread and run over with a whacker plate those voids close and the layer loses roughly a tenth to a quarter of its loose depth. Order the compacted volume and you will finish thin. The other reason to round up is colour. Aggregate from a second delivery, or from a different quarry, frequently does not match the first, and on a visible drive the join between two batches shows for years. A quarter of a bulk bag left over is a far better outcome than having to buy a whole second one.

Tonnes, cubic metres and a density nobody will commit to

The volume is exact arithmetic. Area in square metres multiplied by depth in metres gives cubic metres, and there is nothing approximate about it. The difficulty starts the moment a supplier quotes by the tonne, because converting cubic metres into tonnes needs a density and no British Standard fixes one.

Decorative gravel generally falls between about 1.5 and 1.7 tonnes per cubic metre. That range is not hedging on our part: it is what UK suppliers' own published coverage figures imply when you work backwards from them. Mainland Aggregates quotes an 850 kg bulk bag covering approximately 5 m² at 100 mm, which comes out near 1.7 tonnes per cubic metre. Other merchants publish 75 to 80 kg per square metre at 50 mm, which implies 1.5 to 1.6. Both are honest figures for the material each sells. Density shifts with the parent rock, the grading, the amount of dust in the mix and how much rain the stockpile has taken, and the same product genuinely weighs more in February than in July.

MOT Type 1 is heavier, at roughly 2 tonnes per cubic metre once compacted and nearer 1.7 loose, which is why supplier coverage figures for it look contradictory until you notice which state they are quoting. If you are buying by weight, a two minute phone call asking what that specific product runs per cubic metre is more reliable than any conversion table, this one included. The quarry weighs loads all day and knows the answer.

What is actually in a bulk bag

The bulk bag, or dumpy bag, is the standard domestic unit and it is not a standard volume. It is sold by weight. Guidance agreed between the Builders Merchants Federation and Trading Standards, reported in the trade press, is that aggregate bulk bags should be filled to 900 kg and marked with a minimum weight of 850 kg. In practice merchants advertise them variously at 800 kg, 850 kg, or simply as a bulk bag, so the volume you receive depends entirely on the density of what is inside it.

There is a legal edge to this as well. Under the Weights and Measures Act 1985 aggregate sold in quantities over a tonne must be sold by specific measure rather than as a number of bags, which is part of the reason larger orders arrive loose tipped.

Loose tipped is usually cheaper per tonne, and above about three bags it is worth pricing both ways. The trade-off is where the lorry can tip. A tonne is a considerable pile and every kilogram of it gets moved twice if it lands in the wrong place, so tipping onto a board or a sheet on the hard standing rather than onto the lawn saves more labour than any other decision on delivery day.

MOT Type 1, and why the sub-base decides everything

MOT Type 1 is the British default sub-base: crushed limestone or granite graded from around 40 mm down to dust, to a Department for Transport specification. The fines are the whole point. They fill the voids between the larger pieces so the layer knits under compaction into something close to a solid slab, which is exactly what a driveway, patio or shed base needs beneath it. Washed single-size stone, however handsome, never does this.

Conventional depths are about 75 mm of compacted Type 1 under a path, 100 mm under a patio and 150 mm under a domestic driveway, going to 200 mm on soft clay or where a delivery lorry will use it. Those are trade conventions rather than code requirements, and a groundworker who knows the soil in your area is a better guide than any general rule.

How it goes down matters more than how deep it is. Type 1 consolidates properly in layers of about 50 mm, and 75 mm is the sensible maximum for a plate compactor. Tip 150 mm in one go, run the whacker over it, and the top 50 mm locks up while everything underneath stays loose. It looks finished on the day it is laid and then ruts through the first wet winter, usually exactly where the wheels run.

Choosing the stone and keeping it where you put it

For a drive, 20 mm angular gravel is the usual recommendation. The pieces are large enough and irregular enough to knit together and stay put under a tyre. Rounded 10 mm pea shingle looks lovely and behaves badly: uniform round stones roll over one another, migrate to the edges, lodge in tyre treads and get walked indoors. It belongs as a top dressing, in a border, or held in a grid.

Depth is where people overdo it. Around 40 to 50 mm on paths and borders and 50 to 60 mm on a driveway, laid over a proper sub-base, is what suppliers and installers consistently recommend. Deeper is not better. A hundred millimetres of loose gravel is tiring to walk on, wheels spin in it, and pram and bin wheels sink.

Two things hold the surface together. A cellular gravel grid, laid over the sub-base and filled with stone, all but eliminates migration and is what makes gravel workable on a slope or a turning area. Edging in timber, steel or kerb stops the whole surface creeping into the borders. A geotextile membrane between sub-base and gravel earns its keep on soft or silty ground, where it stops stone being pumped down into the mud over the years, but it is not a substitute for compaction.

One more British consideration. The Planning Portal is explicit that a new or replacement driveway of any size needs no planning permission if it uses a permeable surface such as gravel, or if rainwater is directed to a lawn or border. Permission is required for a traditional impermeable driveway of more than five square metres that does not drain to a permeable area. Gravel sits on the right side of that line, which is a large part of why it remains so common in front gardens.

Gravel coverage by depth

Areas are worked from a density range of 1.5 to 1.7 tonnes per cubic metre, which is what UK suppliers' own published coverage figures imply for decorative gravel. Use the table to sanity-check a quote rather than as a precise order figure. MOT Type 1 is heavier, at roughly 2 tonnes per cubic metre compacted, so a tonne of it covers about 5 m² at 100 mm.

Depth	Covered by 1 tonne	Covered by an 850 kg bulk bag	Cubic metres per 10 m²
25 mm	24–27 m²	20–23 m²	0.25
30 mm	20–22 m²	17–19 m²	0.30
40 mm	15–17 m²	13–14 m²	0.40
50 mm	12–13 m²	10–11 m²	0.50
60 mm	10–11 m²	8–9 m²	0.60
100 mm	6–7 m²	5–6 m²	1.00

Volumes are arithmetic. The 1.5 to 1.7 tonnes per cubic metre range is reverse-engineered from published UK supplier coverage: Mainland Aggregates quotes an 850 kg bulk bag covering about 5 m² at 100 mm, while others quote 75 to 80 kg per square metre at 50 mm. No British Standard fixes a density for decorative aggregate, and we would not quote a single figure. Bulk bag weight follows Builders Merchants Federation and Trading Standards guidance reported in Builders Merchants Journal: filled to 900 kg and marked with a minimum of 850 kg.

What goes wrong on gravel jobs

Ordering by the tonne without asking the density. Tonnes only become cubic metres through a density that varies by product and by how wet the stockpile is. Ask the supplier what their material runs rather than trusting a generic conversion.

Laying the sub-base in one lift. MOT Type 1 consolidates in layers of about 50 mm. A single deep layer packs at the surface only, then ruts through the first wet winter.

Using rounded pea shingle as a driveway surface. Uniform round stone never locks. It migrates to the edges, sits in tyre treads and needs raking back every spring. Angular 20 mm gravel stays put.

Laying the gravel too deep. 50 to 60 mm on a drive and 40 to 50 mm on a path is plenty. Deeper is loose underfoot and wheels spin in it.

Ordering the compacted volume of Type 1. Loose aggregate loses roughly a tenth to a quarter of its depth once compacted. Order the loose volume, not the finished one.

No edging. Without a kerb, steel or timber edge the whole surface migrates into the borders and lawn, and you spend every spring shovelling it back.

Frequently asked questions

How many tonnes of gravel are in a bulk bag?

A standard bulk bag holds about 850 kg — roughly 0.8 tonnes, or around 0.55 m³ of decorative gravel.

How deep should gravel be?

About 4 cm for paths and borders and 5 cm for driveways, laid over a compacted MOT sub-base. Going much deeper wastes stone and feels loose underfoot.

How much does gravel cost in the UK?

Decorative aggregate is roughly £45–£80 per tonne in 2026, plus delivery. Bulk bags are usually the cheaper way to buy for anything above a few square metres.

How much MOT Type 1 do I need under a driveway?

The usual figure is 150 mm of compacted Type 1 under a domestic drive, rising to 200 mm on soft clay or where a delivery lorry will use it, and 75 to 100 mm under paths and patios. Lay it in layers of about 50 mm and compact each one, because a plate compactor cannot consolidate much more than 75 mm at a time. Order the loose volume rather than the finished depth, since Type 1 loses roughly a tenth to a quarter of its depth as it is compacted.

Do I need planning permission for a gravel driveway?

Generally no. The Planning Portal states that a new or replacement driveway of any size does not need planning permission if it uses a permeable surface such as gravel, permeable block paving or porous asphalt, or if rainwater is directed to a lawn or border. Permission is needed for an impermeable driveway of more than five square metres that does not drain to a permeable area. The rules apply to houses rather than flats or maisonettes, and a dropped kerb is a separate application to the highway authority.

What size gravel is best for a driveway?

Angular 20 mm gravel. The pieces are big enough not to be flicked out by tyres and irregular enough to knit together, so the surface holds. Rounded 10 mm pea shingle rolls under load, migrates to the edges and jams in tyre treads. If you want the look of small round stone on a drive, lay it as a thin dressing inside a cellular gravel grid rather than loose.