Gravel Calculator UK: How Much Do You Need?

This gravel calculator works out the volume of gravel you need for a UK garden, driveway, or path in cubic metres and tonnes. You enter the length and width in feet or metres, the depth you want, and it returns the volume in cubic yards and cubic feet, which you can then convert to tonnes using the typical density of gravel. The calculator below uses the standard formula for volume and shows you the result instantly.

Formula

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

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

Since there are 27 cubic feet in a cubic yard, the volume in cubic yards is:

Volume (cubic yards) = Length (ft) × Width (ft) × Depth (in) ÷ 324

Where:

• Length – the longer side of the area in feet (ft).
• Width – the shorter side in feet (ft).
• Depth – how deep you want the gravel layer in inches (in).

The factor 324 comes from 27 (cubic feet per cubic yard) multiplied by 12 (inches per foot). If you measure in metres, the equivalent is: Volume (m³) = Length (m) × Width (m) × Depth (m). One cubic metre equals 1.308 cubic yards.

Worked Example

Using the default values from the calculator – a length of 40 ft, width of 25 ft, and depth of 3 inches:

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 (rounded to 2 decimal places)

The calculator shows 9.26 yd³ and 250.0 ft³, matching the manual calculation.

When to Use the Gravel Calculator

Use this calculator for any project that involves laying a gravel bed over a rectangular area. Common UK applications include:

• Garden paths and walkways
• Driveways and parking areas
• Base layer for sheds, greenhouses, or patios
• Drainage trenches or French drains
• Play areas or decorative borders

The calculator works for any type of loose aggregate – pea gravel, crushed stone, shingle, or slate chippings – because it only calculates volume. To convert volume to weight, you need the density of the specific material, which varies from about 1.4 to 1.7 tonnes per cubic metre for most gravels. A typical value is 1.6 t/m³, but always check with your supplier.

How to Choose the Right Depth

The depth you need depends on the purpose of the gravel:

• 2–3 cm (about 1 inch) – decorative mulch over soil or weed membrane; enough to cover the surface.
• 5 cm (2 inches) – standard for paths and patios that get light foot traffic.
• 7.5–10 cm (3–4 inches) – recommended for driveways where vehicles will park or drive; this depth prevents ruts and spreading.
• 15 cm (6 inches) or more – for heavy-duty bases under block paving or as a sub-base for large vehicles.

If you are laying gravel over a weed membrane, the depth is measured from the top of the membrane, not from the soil below. For driveways, you should also consider a geotextile membrane and possibly a hardcore sub-base underneath the gravel to prevent sinking.

Common Mistakes and How to Avoid Them

People often make these errors when calculating gravel needs:

• Mixing units – entering length in metres but depth in inches. Always convert everything to the same unit before calculating.
• Forgetting to convert depth – depth is usually given in inches or centimetres, but the formula needs it in the same unit as length and width. Our calculator does this for you.
• Rounding too early – if you round the volume to a whole number before converting to tonnes, you can end up ordering too little or too much. Keep at least two decimal places until the final step.
• Not accounting for compaction – some gravels (especially crushed stone) compact down by 10–20% when rolled. If you are laying a driveway, order 10–15% extra to compensate.
• Ignoring the shape – the calculator assumes a perfect rectangle. For irregular areas, break them into rectangles, calculate each, and sum the results.

Converting Volume to Tonnes

Gravel is usually sold by weight in the UK (per tonne) or by volume (per cubic metre). To convert cubic yards to tonnes, use the density of your specific gravel. The formula is:

Weight (tonnes) = Volume (m³) × Density (t/m³)

Since 1 cubic yard = 0.7646 cubic metres, you can convert the calculator’s output to tonnes as follows:

1. Take the volume in cubic yards (e.g., 9.26 yd³).
2. Convert to cubic metres: 9.26 × 0.7646 = 7.08 m³.
3. Multiply by the density (e.g., 1.6 t/m³): 7.08 × 1.6 = 11.33 tonnes.

So for the default example, you would need about 11.3 tonnes of gravel with a density of 1.6 t/m³. Always confirm the density with your supplier – it can vary from 1.4 for light pea gravel to 1.7 for crushed granite.

Ordering and Delivery Considerations

Once you have your volume or weight, you need to decide how to buy it. In the UK, gravel is available in:

• Bulk bags (approx. 0.5–1 m³) – most economical for large projects; delivered on a pallet.
• Small bags (20–25 kg) – convenient for small areas or top-ups; you’ll need many for a driveway.
• Loose tipped – for very large quantities, delivered by a tipper lorry; requires access for the vehicle.

If you buy in bulk bags, remember that a 1 m³ bag of gravel weighs about 1.5–1.7 tonnes, so check your vehicle’s load capacity if you collect it yourself. For delivery, make sure the driver can access the drop-off point – gravel is heavy, and bags are not moved far from the lorry.

Always order a little extra (5–10%) to cover spillage, compaction, and uneven ground. It’s cheaper to have a bag left over than to run out halfway through the job.

Frequently Asked Questions

How many tonnes of gravel do I need for a 100 m² driveway at 5 cm depth?

First, calculate the volume: 100 m² × 0.05 m = 5 m³. Then multiply by the density (e.g., 1.6 t/m³): 5 × 1.6 = 8 tonnes. So you would need about 8 tonnes of gravel for a 100 m² driveway at 5 cm depth.

What depth of gravel do I need to stop weeds?

For decorative gravel over a weed membrane, 3–5 cm (1–2 inches) is usually enough to block light and prevent weed growth. If you don’t use a membrane, you’ll need at least 7–10 cm to discourage weeds, but they will still find their way through eventually.

Can I use the calculator for circular areas?

No, this calculator is for rectangular areas only. For a circle, use the formula π × (radius)² × depth. For example, a circular path with a 2 m radius and 5 cm depth: 3.14 × 4 × 0.05 = 0.63 m³.

How do I measure an irregular-shaped garden?

Break the area into rectangles, triangles, or circles. Calculate each separately, then add the volumes together. For triangles, the area is ½ × base × height. For circles, use π × radius².

What is the difference between gravel and shingle?

In the UK, the terms are often used interchangeably, but technically gravel refers to small stones (2–64 mm) that are naturally rounded or crushed, while shingle specifically means rounded, water-worn stones, often from the beach. For most projects, the difference is cosmetic – the calculator works for both.

Should I lay a membrane under gravel?

Yes, a weed membrane (geotextile) is strongly recommended. It prevents weeds from growing through the gravel, stops the gravel from sinking into the soil, and improves drainage. It costs little and saves hours of weeding later.

Related

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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