Gravel Calculator: How Much Gravel Do I Need?
Work out how many tonnes and bags of gravel, chippings or slate you need for a path, border or driveway, plus the MOT Type 1 sub-base and weed membrane to go underneath.
No sign-up required. Free to use, with every formula shown on this page. Last reviewed October 2026.
Work out your gravel
Gravel Calculator
Work out how much gravel, chippings or sub-base a path, border or driveway needs, in tonnes and in bags, with weed membrane to go underneath.
1 Where it's going
What it's for Areas to coverSplit an odd shape into rectangles and circles, or enter the m² if you know it.
Areas to leave out2 The gravel
Type of stoneYour merchant can tell you, or it's on their website.
3 Under the gravel
A firm, compacted layer of crushed stone. Driveways need about 150 mm; paths on soft ground 75–100 mm.
Stops weeds and keeps the gravel from sinking into the soil. We add 10% for the overlaps.
4 Prices (optional)
Add the prices you've seen to get a total. Leave any box empty to skip it.
Gravel you need
0 tonnes
Area
0 m²
Volume
0 m³
1 tonne covers
–
What you'll need
Breakdown
| Area | Size | m² |
|---|
How it's worked out: volume = area × depth. Weight = volume × the weight of one m³ of the stone (gravel and pea shingle 1,7 t, chippings 1,6 t, slate 1,4 t, cobbles 1,5 t), plus the extra %. Bags = weight ÷ bag size, rounded up. Sub-base: area × compacted depth × 2,1 t per m³ (MOT Type 1), plus the same extra. Weed membrane: area + 10% for overlaps.
Estimates only. The weight of a m³ varies with the stone, its size and how wet it is: check the figure your merchant gives. Measure the area on the ground, and order a little more rather than less: a second delivery usually costs more than a few spare bags.
How it works
Area, depth and weight
Gravel is sold by weight, but you need it by volume: enough to cover the ground to the right depth. The calculator works out the volume, then turns it into tonnes and bags. The sources and assumptions behind it are on our How we calculate page.
Measure the area
Add up the areas you’re covering: rectangles (length × width), circles, or a known number of m². Take away anything you’re leaving out, such as a shed base, a pond or a tree. Split an odd shape into rectangles and circles.
Choose the depth
40 mm suits borders and the ground under decking; 50 mm suits paths and driveways. Volume = area × depth, so 12 m² at 50 mm is 0.6 m³. Deeper loose gravel is hard to walk on, so a driveway gets its strength from a sub-base underneath instead.
Turn it into tonnes and bags
One m³ of gravel weighs about 1.7 tonnes (slate is lighter, at about 1.4). Tonnes = m³ × that weight, plus a little extra for settling and uneven ground. Bags = tonnes ÷ the bag size, rounded up.
Examples
How much gravel do I need?
The same calculator, a few common jobs. As a rule of thumb, a tonne of gravel covers about 12 m² at 50 mm deep, and an 850 kg bulk bag about 10 m².
Illustrative only, from the calculator above, with 5% extra. Gravel and pea shingle at 1.7 tonnes per m³, decorative chippings 1.6, slate 1.4, MOT Type 1 compacted 2.1. “1 + 2 × 25 kg” means one bulk bag topped up with small bags, when a second bulk bag would be mostly left over.
Tips
Before you order
Getting the quantity right is half the job; the other half is the ground underneath and getting it delivered.
Bulk bags or small bags?
Small 20 or 25 kg bags are easy to carry and good for a border or a round bed. Past about 30 bags, an 850 kg or 1 tonne bulk bag is usually cheaper. Bulk bags come on a lorry with a crane, so check it can reach your drive or the kerb: a full bag can’t be moved by hand.
Prepare the ground
Dig out the turf and soil to the depth you need and level it. For a driveway, lay about 150 mm of MOT Type 1 and compact it with a plate compactor in layers of about 75 mm; for a path on soft ground, 75–100 mm. Edging keeps the gravel off the lawn.
Lay a weed membrane
A permeable weed membrane stops weeds coming through and the gravel sinking into the soil. Overlap the joins by about 10 cm and pin it down with pegs about every metre. On a driveway it goes on top of the sub-base, under the gravel.
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Common questions
Frequently asked questions about how much gravel you need
Common questions about tonnes, bags, depth and what goes underneath.
How much gravel do I need?
Multiply the area in m² by the depth in metres to get the volume in m³, then multiply by about 1.7 to get the tonnes of gravel. A path 10 m long and 1 m wide at 50 mm deep is 0.5 m³, or about 0.9 tonnes with a little extra. The calculator works it out for your own areas, stone and bags.
How many m² does a tonne of gravel cover?
About 12 m² at 50 mm deep, or about 15 m² at 40 mm. Lighter stone, such as slate chippings, covers a little more for the same weight; bigger cobbles a little less.
How deep should gravel be?
30–50 mm for borders, beds and under decking; 40–50 mm for paths and driveways. Deeper than about 50 mm, loose gravel is hard to walk on and tyres sink into it, so a driveway needs a firm sub-base instead of more gravel.
How many bags of gravel are in a tonne?
40 bags of 25 kg, or 50 bags of 20 kg. A bulk bag usually holds 850 kg in the UK, or 1 tonne (often called a big bag) in Ireland and much of Europe.
How much does a bulk bag of gravel cover?
An 850 kg bulk bag covers about 10 m² at 50 mm deep, or about 12 m² at 40 mm. Check the merchant’s own figure, because the weight per m³ varies with the stone.
Do I need a sub-base for a gravel driveway?
Yes. A driveway needs about 150 mm of compacted MOT Type 1 under the gravel, or the gravel sinks and ruts. Compact it in layers with a plate compactor. A path on firm ground can often go without, but 75–100 mm helps on soft or clay soil.
Do I need weed membrane under gravel?
It’s not essential, but it helps: a permeable membrane stops most weeds from below and keeps the gravel from mixing into the soil. Overlap the joins and pin it down. Weeds can still grow in the gravel from seeds that blow in, so it won’t stop all of them.
Are the results exact?
No. They are estimates: the weight of a m³ varies with the stone, its size and how wet it is, and the ground is never perfectly level. The calculator adds 5% by default and rounds the bags up; order a little more rather than less, because a second delivery usually costs more than a few spare bags.