Gravel Calculator: How Much Gravel, Tonnes and Bulk Bags Do You Need?
Planning a driveway, a garden path or a new border? This free gravel calculator tells you how much gravel to order before you spend a penny. Enter the size of your area, choose the depth and your type of stone, and you’ll see the volume, the weight in tonnes and the number of bulk bags in a few seconds.
It handles rectangles, circles, triangles and any area you already know, in metric or imperial units. It also covers popular stones such as pea gravel, decorative gravel, slate and Cotswold stone chippings, and it adds a sensible extra for settling and waste. Everything runs in your browser, so nothing you type is stored or sent anywhere.
- Free to use
- Metric and imperial
- Tonnes, bags and cost
Everything is calculated in your browser. Nothing is sent to a server or saved.
How to use this gravel calculator
Pick your units
Choose metric for metres and millimetres, or imperial for feet and inches. Your numbers convert when you switch.
Measure the area
Select a shape and type in its size. If you already know the area from a plan, choose the known area option and enter it directly.
Set depth and stone
Enter how deep you want the gravel and choose your stone. Not sure about depth? The depth guide below will help.
Get your numbers
Press calculate to see volume, tonnes, bulk bags and an optional cost. The diagram next to the form updates as you type.
How the gravel calculator works
The maths is straightforward, and you can check any result by hand. Here’s what happens behind the button.
1. Area
Rectangles use length × width. Circles use π × radius squared. Triangles use half of the base × height.
2. Volume
Area × depth gives the volume of gravel. A 12 m² area at 50 mm deep (0.05 m) needs 0.6 m³.
3. Weight
Volume × density gives the weight. Loose gravel is usually around 1.5 to 1.7 tonnes per m³, so 0.6 m³ weighs roughly 0.96 tonnes.
4. Extra allowance
Gravel settles once it’s laid, and a little always goes missing at the edges. We add 10% by default. Raise it for uneven ground or lower it for a tidy, flat bed.
5. Bulk bags
Total weight ÷ bag weight, rounded up to a whole bag. Bulk bags of stones usually hold 800 kg to 1 tonne, but always check your supplier’s exact figure.
6. Cost
Add a price per tonne, a price per bag or both, and you’ll get a rough total in whatever currency you use.
A worked example
Say you want a path 10 m long and 1.2 m wide at 40 mm deep, using 20 mm gravel. The area is 12 m². At 0.04 m deep that’s 0.48 m³. At 1.6 tonnes per m³ that’s 0.768 tonnes, and with 10% extra you need about 0.84 tonnes. That’s one 850 kg bulk bag, or 34 bags of 25 kg.
Why it’s an estimate
Density changes with the type of stone, how wet it is and how tightly it’s packed. Treat the answer as a solid starting point, and confirm the bulk density and bag weight with your supplier before you order.
How deep should gravel be?
The right depth depends on what the gravel is for. On a driveway, gravel is only the top layer, and a compacted sub base usually goes underneath. To work that out separately, pick MOT Type 1 in the stone list.
Garden paths
30 to 40 mm. Enough to hide the base and feel firm underfoot.
Borders and planters
25 to 40 mm. A thinner layer looks good, and a weed membrane underneath does the heavy lifting.
Driveways
50 mm is the usual depth for the top layer. Angular 20 mm stone knits together better than rounded pea gravel.
Heavy use and drainage
75 to 100 mm. Suits regular heavy vehicles or drainage runs, with the right sub base below.
How much does a tonne of gravel cover?
These figures assume gravel at 1.6 tonnes per m³, before any extra allowance. Lighter stone such as slate covers more area per tonne, and heavier stone covers less.
25 mm deep
About 25 m² per tonne.
30 mm deep
About 20.8 m² per tonne.
40 mm deep
About 15.6 m² per tonne.
50 mm deep
About 12.5 m² per tonne.
75 mm deep
About 8.3 m² per tonne.
100 mm deep
About 6.3 m² per tonne.
Gravel types and typical weights
Different stones weigh different amounts, so the calculator uses a typical loose density for each one. These are common trade figures. Your supplier’s own numbers may differ a little.
Pea gravel, 10 mm
About 1.6 tonnes per m³. Small, rounded and comfortable underfoot, so it’s popular for paths and play areas.
Decorative gravel, 20 mm
About 1.6 tonnes per m³. The all round choice for driveways, borders and larger gardens.
Cotswold stone chippings
About 1.5 tonnes per m³. Warm, honey coloured limestone that suits period homes and country gardens.
Slate chippings
About 1.4 tonnes per m³. Flat pieces that are lighter, so a tonne covers more ground.
MOT Type 1 sub base
About 1.9 tonnes per m³. A dense, crushed base layer that goes under a gravel driveway or path.
Your own stone
Got a density figure from your supplier? Choose the custom option and type it in for a more exact result.
Cotswold stone chippings: how much do you need?
Quick way to work it out
Choose Cotswold stone chippings in the stone list, then enter your area and depth. At 50 mm deep, one tonne covers roughly 13 m², a little more than heavier stones such as granite. For a small front path, that often means just a single bulk bag.
Order from one batch
Cotswold stone is a natural limestone, so colour and density can vary from batch to batch. Ask your supplier for the exact bulk density, and order everything in one go so the colour stays even across the whole area.
Bulk bags of stones: what to know before you order
Typical sizes
Bulk bags of stones commonly hold 800 kg to 1 tonne. Small bags of 20 kg or 25 kg suit tight access and little jobs. Pick your bag size in the calculator.
How many bags
We divide the total weight by the bag weight and round up to a whole bag. One 850 kg bag of 20 mm gravel covers about 10 m² at 50 mm deep.
Delivery and handling
A full bulk bag is very heavy. Check where the lorry can drop it and how you’ll move the stone. For big jobs, a loose delivery can work out cheaper if you have space to tip it.
Using this gravel calculator with Gravel Master and other suppliers
An independent estimate
Gravel Master is a UK supplier of decorative aggregates, and many other suppliers and builders’ merchants offer their own gravel calculators. This tool is independent and isn’t connected to any supplier. It’s a quick way to get a realistic figure before you start comparing prices.
Compare before you buy
Run your measurements here first, then check the tonnes and bags against each supplier’s own numbers. Small differences are normal, because every supplier uses its own stone density and bag weight.
Tips for ordering gravel
Measure twice
Small errors add up fast. Measure the widest and narrowest parts of an uneven area and use the average.
Order a little extra
A second delivery costs more than an extra half bag, and a new batch can look slightly different.
Check the bag weight
Bulk bags aren’t all the same size. Confirm the weight before you pick a bag size in the calculator.
Prepare the base
Lay a weed membrane and a firm base first. Gravel on bare soil sinks and mixes with the earth.
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Frequently asked questions
How do I calculate how much gravel I need?
Multiply the area by the depth to get the volume, then multiply by the density of your gravel to get the weight. Add about 10% extra for settling and waste. The calculator above does all of that for you and turns the result into tonnes and bulk bags.
How many tonnes of gravel do I need for a driveway?
It depends on the size. As a guide, a single parking space of 15 m² (5 m by 3 m) at 50 mm deep needs about 1.3 tonnes of 20 mm gravel including 10% extra. Enter your own measurements for an exact figure.
How many bulk bags of stones do I need?
Divide the tonnes you need by the weight of one bag and round up. An 850 kg bag of 20 mm gravel covers roughly 10 m² at 50 mm deep, so a 30 m² area at that depth needs around three bags, or four once you add a 10% allowance.
How much does a tonne of gravel cover?
For gravel at 1.6 tonnes per m³, one tonne covers about 12.5 m² at 50 mm deep, 15.6 m² at 40 mm and 25 m² at 25 mm.
How much is a tonne of gravel in cubic metres?
At 1.6 tonnes per m³, one tonne is about 0.63 m³. Lighter stone such as slate takes up more space per tonne, and heavier stone takes up less.
How much extra gravel should I order?
Ten percent is a good starting point. Go higher if the ground is uneven or if you’re topping up an old surface, and lower if the bed is flat and neat.
What’s the difference between a tonne and a ton?
A metric tonne is 1,000 kg. A US ton is about 907 kg. The calculator shows both, so you can compare quotes in either unit.
How much Cotswold stone do I need?
Pick Cotswold stone chippings in the stone list and enter your area and depth. At 50 mm deep, one tonne covers about 13 m².
Is this the same as the Gravel Master calculator?
No. This gravel calculator is independent and isn’t connected to Gravel Master or any other supplier. Suppliers use their own densities and bag weights, so their figures can differ a little from ours.
Is my data saved anywhere?
No. Everything is calculated inside your browser. Nothing is uploaded, stored or shared.