Area (for a known total area, put that figure in length and set width to 1)
Depth
Gravel size is a separate choice from depth: 10mm gravel is the usual pick for footpaths and borders, where a finer stone sits comfortably underfoot, while 20mm is more common on driveways because larger stones are less likely to migrate under tyres or scatter when walked on. The density default below (1.6 t/m3) assumes typical 20mm gravel; finer or angular gravels can sit slightly either side of that.
Driveway gravel over 50mm sits on a compacted sub-base, not bare soil or a shallow scrape - the sub-base itself is usually 100-150mm of MOT Type 1 or similar, worked out separately with the aggregate calculator. This page covers the decorative gravel layer on top, not what goes underneath it.
| Volume | Amount |
|---|
Buying it (density and bulk bag weight are typical figures - edit if your supplier quotes different)
| Volume | 0.00 m3 |
| Bulk bags | 0 |
| 25kg bags | 0 |
How this calculator works
Take a 4m by 3m path: multiply those two figures for area, then bring in the depth - the field takes millimetres, but the sum needs metres, so it divides by 1000 automatically. Only measured the whole plot as one figure? Put it straight into the length box and set width to 1. That raw figure then gets a settling top-up, since loose gravel beds down once walked on or driven over and raking it level always leaves a bit of unevenness. Gravel settles less than a soil-based material like topsoil, so 5% covers most decorative jobs; a driveway under regular wheel traffic is safer nearer 10%.
Choosing depth for the job
Depth is a job decision, not a gravel-size one. A path or border only needs to hide the membrane and give the stone something to sit in, so 30-40mm is typically enough. A driveway needs a slightly thicker top layer, around 50mm, because a thin scatter wears thin in tyre tracks within a season. Drainage and soakaway work is different again: the gravel is doing a job there, letting water through rather than sitting flat for looks, so 100mm or more is typical and depends on the drainage design itself.
Tonnes versus bulk bags versus 25kg bags
Gravel is bought three ways: loose by weight, in bulk bags, or in 25kg poly bags, and every figure below starts from this calculator's own 1.6 t/m3 default density (finer or damp gravel can sit slightly either side). A small border rarely needs more than a bag or two, so a 25kg pack makes sense despite costing the most per tonne - divide 25 by 1.6 and a bag works out to 15.625 litres, so expect 15-16 litres depending on exactly how the stone settles. Past a handful of bags, a bulk bag is the better buy: expect roughly 850kg of usable gravel per bag, sometimes quoted instead as close to 0.7 m3 - a separate rule of thumb, not a strict match, since bags are rarely packed to a precise level. Bag counts on this page come from the weight figure, not the volume one.
Do I need a membrane under gravel?
Yes, typically. A permeable weed membrane laid before the gravel stops weeds rooting into the ground beneath and keeps the stone from working its way down into the soil, which is what makes a gravel path look thin and patchy after a few years. It's not usually needed under a driveway sub-base, where the compacted stone does that job, but it's standard under the decorative top layer this calculator covers.
What this calculator does not check
Quantity is the whole job here - style and structure aren't. Sub-base depth for a driveway is worked out separately, with the aggregate calculator rather than this one; edging to stop stone spreading onto a lawn or path isn't covered at all; and neither is which colour or stone size actually suits the space - a handful of samples from a merchant settles that faster than any number on a screen.
Related tools
Need the compacted layer that sits under a driveway before gravel goes on top? The aggregate calculator takes the same length, width and depth inputs and turns them into sand, topsoil or compacted hardcore figures instead, and it's the right choice whenever the layer in question is structural rather than decorative. Filling a border with fresh soil before the gravel goes down? The topsoil calculator covers that half separately.
FAQ: how much gravel do I need
How much gravel do I need for a path? For a 4m × 3m path (12 m2) at the path/border preset depth of 40mm, the raw volume is 12 × 0.04 = 0.48 m3. A 5% settling allowance brings that up to 0.48 × 1.05 = 0.504 m3. At the default 1.6 t/m3 density that's 0.504 × 1.6 = 0.8064 tonnes, shown rounded as 0.81 tonnes - 1 bulk bag (a single 0.85t bag covers it) or 33 x 25kg bags (806.4kg ÷ 25 = 32.3, rounded up to the next whole bag, since no merchant sells a fraction of one).
How deep should gravel be? 30-40mm for a path or border, 50mm for a driveway on a proper sub-base, 100mm or more for drainage - see the depth section above for why.
Tonnes or bulk bags, which should I buy? Buying loose gravel and having it tipped is the cheapest option per tonne once a job is bigger than a garden border, provided delivery access allows it. A bulk bag costs somewhat more but only needs space to drop it, not full vehicle access. 25kg bags suit the smallest top-up jobs only.
Do I need a membrane under gravel? Yes, typically, for a path, border or bed - see the membrane section above for the driveway exception.
How is this different from the aggregate calculator? The aggregate calculator is the general-purpose tool, covering gravel alongside sand, topsoil and hardcore/MOT Type 1 with a single depth field for whatever the job needs. This page narrows in on gravel specifically: decorative-job depth presets, gravel-size guidance and the membrane question above, none of which the wider tool sets out to cover.