Gravel Calculator UK: How Much Do I Need?

This gravel calculator works out the volume of gravel you need for a UK garden, driveway, or path. You enter the length and width of the area in feet or metres, plus the depth you want, and it returns the volume in cubic yards and cubic feet. The result tells you exactly how much gravel to order, so you don’t end up with too little (and a half-finished job) or too much (and a pile you have to store).

Formula

The calculator uses the basic volume formula for a rectangular box:

Volume (ft³) = Length (ft) × Width (ft) × Depth (in) ÷ 12

Then converts cubic feet to cubic yards, since gravel in the UK is usually sold by the tonne or by the cubic yard:

Volume (yd³) = Volume (ft³) ÷ 27

Or in one step: yd³ = (L × W × D) / 324 because 27 × 12 = 324.

Variables:

• L – length of the area, in feet (or metres, if you convert first)
• W – width of the area, in feet
• D – depth of gravel, in inches

If you measure in metres, multiply the result in cubic yards by 0.7646 to get cubic metres, or just use the cubic feet result and divide by 35.315.

Worked Example

Using the default values from the calculator – a 40 ft × 25 ft area at 3 inches deep:

1. Convert depth to feet: 3 in ÷ 12 = 0.25 ft
2. Calculate volume in cubic feet: 40 × 25 × 0.25 = 250 ft³
3. Convert to cubic yards: 250 ÷ 27 = 9.26 yd³

The calculator shows 9.26 yd³ (rounded to two decimal places) and 250 ft³. That matches the formula exactly.

How to Measure Your Area

Most UK gardens aren’t perfect rectangles, so you’ll need to break the area into shapes and add them up.

• Rectangles and squares: length × width.
• Triangles: (base × height) ÷ 2.
• Circles: Ï€ × radius².
• Irregular shapes: split into rectangles, roughly trace the outline, or use an online map tool to plot the area.

Measure in feet and inches or metres consistently. If you mix units, you’ll get a wrong answer. A 10 m × 5 m area is not the same as 10 ft × 5 ft – convert everything to one unit first.

Choosing the Right Depth

The depth you need depends on what the gravel is for:

• Paths and walkways: 2–3 inches (50–75 mm)
• Driveways (regular car traffic): 4–6 inches (100–150 mm) – often laid in two layers
• Decorative borders and beds: 1–2 inches (25–50 mm)
• Under sheds or as a base: 4 inches (100 mm) or more

Going thinner than 2 inches means weeds will push through and the gravel will shift. Going thicker than 6 inches is usually wasteful unless you’re building a heavy-duty base. For driveways, you also need a sub-base of hardcore or MOT Type 1, which this calculator does not include – that’s a separate layer.

Common Mistakes and How to Avoid Them

The most frequent errors when calculating gravel are:

• Mixing units: entering length in metres but depth in inches. Convert everything to the same unit first.
• Forgetting to convert depth: depth in inches must be divided by 12 to get feet.
• Ordering by volume instead of weight: gravel is sold by the tonne in the UK. One cubic yard of gravel weighs about 1.4–1.7 tonnes depending on the type and moisture. Multiply your cubic yards by 1.5 for a typical estimate, but check with your supplier.
• Rounding too early: if you round 9.26 to 9, you’ll be short. Always round up to the next whole bag or tonne.
• Ignoring the sub-base: for driveways, the gravel depth is just the top layer; the hardcore beneath is extra.

How Much Does Gravel Weigh?

Gravel density varies. A cubic yard of loose gravel typically weighs between 2,800 and 3,400 pounds (1.4–1.7 tons). In metric, that’s about 1.4–1.7 tonnes per cubic metre. The exact weight depends on the stone type – limestone is heavier than slate, and wet gravel weighs more than dry.

When you order, suppliers in the UK usually quote per tonne. To convert your cubic yards to tonnes, multiply by the density. For example, 9.26 yd³ × 1.5 = 13.9 tonnes. Always ask your supplier for their specific density, as it varies.

Bags vs. Bulk Delivery

For small areas, you can buy gravel in bags (usually 25 kg or 50 kg). A 25 kg bag covers roughly 0.4 m² at 50 mm depth. For larger areas, bulk delivery in tonnes is more economical.

To work out how many bags you need:

1. Calculate the volume in cubic metres (or cubic feet).
2. Divide by the volume of one bag (a 25 kg bag of gravel is about 0.015 m³).
3. Round up to the nearest whole bag.

For a 40 ft × 25 ft area at 3 inches, you’d need about 9.26 yd³ = 7.08 m³. That’s about 472 bags of 25 kg – clearly a bulk delivery is the sensible option.

Frequently Asked Questions

How many tonnes of gravel do I need for a driveway?

First, calculate the volume in cubic yards using the calculator. Then multiply by the density – typically 1.5 tonnes per cubic yard. For a 40 ft × 25 ft driveway at 4 inches deep, that’s 12.35 yd³ × 1.5 = 18.5 tonnes. Add 10% for compaction and settling.

What depth of gravel do I need to stop weeds?

You need at least 2–3 inches (50–75 mm) of gravel to suppress weeds effectively. Lay a weed membrane underneath first – that does more than the depth. If you use less than 2 inches, weeds will find their way through.

Can I use this calculator for pea shingle or decorative stones?

Yes, the volume calculation is the same for any type of loose aggregate. The only difference is the weight per cubic yard, which varies by stone type. For pea shingle, use a density of about 1.4 tonnes per cubic yard.

How do I convert cubic yards to tonnes?

Multiply the cubic yards by the density in tonnes per cubic yard. A typical value is 1.5, but it can range from 1.3 to 1.7. Check with your supplier for the exact density of the gravel you’re buying.

Should I order extra gravel?

Yes, order about 10% more than the calculated volume. Gravel compacts and settles, and you’ll lose some to uneven ground. It’s better to have a small surplus than to run out mid-job.

What if my area is not a rectangle?

Break it into rectangles, triangles, and circles, calculate each separately, and add them together. Or use an online map tool to draw the area and get the square footage. Then enter the total length and width that gives the same area.

Related

• Lawn Edging Calculator: Pieces and Stakes
• Paver Base Calculator: Gravel Base and Bedding Sand
• Topsoil Calculator: Cubic Yards and Tons

in l | Lawn length | ft | 40 | 0 | 100000
in w | Lawn width | ft | 25 | 0 | 100000
in d | Depth | in | 3 | 0 | 120
out yd | Volume | yd³ | l * w * d / 324 | 2
out ft3 | Volume | ft³ | l * w * d / 12 | 1