Gravel Calculator: How Much Gravel Do I Need?

You need to know three measurements: length, width, and depth. Multiply these together to get volume in cubic metres, then multiply by 1.6 to convert to tonnes of gravel. For most driveways and paths, you’ll need between 40-60mm depth of gravel.

That’s the quick answer. But buying the wrong amount costs you time and money. Order too little and you’ll pay delivery twice. Order too much and you’re left with a pile of expensive stone you don’t need.

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Gravel Measurements

Gravel gets sold two ways in the UK: by volume (cubic metres) or by weight (tonnes). Most suppliers prefer tonnes because it’s more accurate.

A cubic metre of gravel weighs roughly 1.6 tonnes. This varies slightly depending on the stone type. Dense aggregates like granite weigh more than lighter limestone.

Why You Can’t Just Measure in Metres

Your brain naturally thinks in flat measurements. You measure your driveway and think “that’s 20 square metres.”

But gravel has depth. You’re filling a three-dimensional space. That 20 square metre driveway at 50mm depth needs 1 cubic metre of gravel, which equals 1.6 tonnes.

The Basic Gravel Calculator Formula

Here’s the formula that works for any rectangular or square area:

Length (m) × Width (m) × Depth (m) × 1.6 = Tonnes needed

Let’s break this down properly.

Step One: Measure Your Area

Get a tape measure. Measure in metres for easier calculations.

For a rectangular driveway:

• Length: 10 metres
• Width: 3 metres
• Planned depth: 50mm (0.05 metres)

Always convert millimetres to metres by dividing by 1000. So 50mm becomes 0.05m.

Step Two: Calculate Volume

10m × 3m × 0.05m = 1.5 cubic metres

Step Three: Convert to Tonnes

1.5 cubic metres × 1.6 = 2.4 tonnes

You’d order 2.5 tonnes from your supplier. Always round up slightly. Running short halfway through a project is frustrating.

How Much Depth Do You Actually Need

Depth makes the biggest difference to your final quantity and your project’s success.

Driveway Gravel Depth

You need 50-60mm minimum for a functional driveway. Any less and you’ll see the membrane or ground underneath. Vehicles will create ruts and distribute the gravel unevenly.

For heavy vehicles or commercial use, go to 75-100mm depth.

Garden Path Depth

40-50mm works perfectly for pedestrian paths. You’re not dealing with vehicle weight, so you can use less material.

Decorative Garden Areas

30-40mm covers beds and borders adequately. This provides good coverage and weed suppression without excessive cost.

Project Type	Minimum Depth	Recommended Depth	Heavy Use Depth
Driveway	50mm	60mm	75-100mm
Garden path	40mm	50mm	60mm
Decorative borders	30mm	40mm	50mm
Parking area	60mm	75mm	100mm

Calculating Gravel for Different Shapes

Not everything is rectangular. Here’s how to handle other shapes.

Circular Areas

For a circular driveway or patio:

3.14 × Radius² × Depth × 1.6 = Tonnes

If you have a circular area with a 3-metre radius and 50mm depth:

• 3.14 × (3 × 3) × 0.05 × 1.6 = 2.26 tonnes

Order 2.5 tonnes.

Irregular Shapes

Break complex shapes into rectangles and triangles. Calculate each section separately, then add them together.

For triangular sections: (Base × Height ÷ 2) × Depth × 1.6 = Tonnes

Curved Paths

Measure the length along the curve. Use the average width. Treat it like a rectangle with those dimensions.

Choosing the Right Gravel Size

Size affects both coverage and quantity needed. Larger stones have bigger gaps between them.

Common UK Gravel Sizes

10mm gravel (pea gravel): Compact surface, smooth underfoot, good for paths. Covers about 100kg per square metre at 50mm depth.

20mm gravel: Most popular all-rounder. Works for driveways and paths. Standard coverage is 80kg per square metre at 50mm depth.

40mm gravel: Larger decorative stone. Less stable for driveways but dramatic in borders. Needs more depth for proper coverage.

The larger the stone, the more gaps between pieces. You might need 10-15% more material with 40mm stones compared to 20mm for the same coverage.

Gravel Types and Their Uses

Cotswold gravel: Honey-coloured limestone. Popular for traditional looks. Good drainage.

Slate chippings: Blue-grey, angular pieces. Contemporary appearance. Doesn’t migrate as easily as rounded gravel.

Flint gravel: Rounded beach-style stones. Natural appearance. Can be difficult to walk on when deep.

Granite chippings: Hard-wearing, angular. Excellent for driveways. Available in multiple colours.

Each type has the same basic calculation method, but their density varies slightly. The standard 1.6 multiplier works for most aggregates sold in the UK, according to the Mineral Products Association, the trade body for UK aggregate suppliers.

The Ground Preparation Factor

Your calculations assume a level base. Real ground isn’t level.

Adding Extra for Uneven Surfaces

If your ground has dips, hollows, or slopes, add 10-20% extra material to your calculated amount.

For a seriously uneven area, consider these options:

• Level the ground first with a base layer of MOT Type 1
• Increase your gravel order by 25%
• Accept that some areas will be deeper than others

The Compaction Reality

Gravel settles. Over the first few weeks, your 50mm depth might compact to 45mm.

This matters for driveways. Vehicles compress the stones. Add an extra 10-15% to your order for areas with vehicle traffic.

Practical Example: A Complete Driveway

Let’s work through a real project.

You have a driveway that’s:

• 12 metres long
• 2.8 metres wide
• Needs 60mm gravel depth
• Has a slight slope (uneven ground)

The Calculation

Base calculation: 12m × 2.8m × 0.06m = 2.016 cubic metres

Convert to tonnes: 2.016 × 1.6 = 3.23 tonnes

Add 15% for uneven ground: 3.23 × 1.15 = 3.71 tonnes

Add 10% for compaction under vehicles: 3.71 × 1.10 = 4.08 tonnes

Order: 4.5 tonnes

This gives you a small buffer. Much better than running short.

Common Gravel Calculator Mistakes

Mistake One: Forgetting Depth Conversion

You measure depth in millimetres but length in metres. You must convert everything to the same unit.

50mm depth is 0.05m, not 5m or 0.5m.

This mistake can make you order 100 times too much or too little.

Mistake Two: Ignoring Edging

If you’re installing edging or borders, these reduce your actual gravel area. A 100mm edging border all around a 10m × 3m area reduces the gravel space to 9.8m × 2.8m.

Small difference, but it matters when you’re trying to order precisely.

Mistake Three: Not Accounting for Existing Ground Cover

Removing turf or old gravel affects your measurements. If you’re removing 30mm of old material and replacing it with 50mm of new, you only need material for the additional 20mm plus whatever’s needed to bring the level up.

Measure from the prepared base level, not from the original ground level.

Mistake Four: Assuming Flat Coverage

Gravel naturally forms small peaks and valleys. A perfectly flat 50mm is theoretical. In reality, coverage varies from 40-60mm across the surface.

This is why the 10% buffer is important.

Ordering Your Gravel

Bulk Bags vs Loose Loads

Bulk bags (also called jumbo bags or tonne bags) typically hold 850kg of gravel. They’re convenient for small projects and easier to store if you’re working gradually.

Loose loads come tipped from a lorry. Cheaper per tonne for large projects. You need space for delivery and must use the gravel quickly.

For our 4.5-tonne driveway example, you’d need either:

• 6 bulk bags (6 × 850kg = 5.1 tonnes)
• One loose load delivery of 4.5-5 tonnes

Delivery Considerations

Large lorries need access. Measure your driveway width, gate width, and overhead clearance.

Standard delivery lorries need:

• 3 metres width clearance
• 4 metres height clearance
• Firm ground to support 20+ tonnes

If access is difficult, bulk bags delivered on a smaller vehicle might be your only option, even if it costs more.

Gravel Coverage Table for Quick Reference

This table assumes 1.6 tonnes per cubic metre and standard 20mm gravel.

Area (m²)	30mm depth	40mm depth	50mm depth	60mm depth	75mm depth
5	0.24t	0.32t	0.40t	0.48t	0.60t
10	0.48t	0.64t	0.80t	0.96t	1.20t
15	0.72t	0.96t	1.20t	1.44t	1.80t
20	0.96t	1.28t	1.60t	1.92t	2.40t
25	1.20t	1.60t	2.00t	2.40t	3.00t
30	1.44t	1.92t	2.40t	2.88t	3.60t
40	1.92t	2.56t	3.20t	3.84t	4.80t
50	2.40t	3.20t	4.00t	4.80t	6.00t

Use this for quick estimates. Then add your buffer for ground conditions.

Cost Planning

Gravel prices vary significantly by region and stone type.

Budget gravel (crushed concrete or basic limestone): £40-£60 per tonne delivered

Standard decorative gravel (Cotswold, basic granite): £60-£90 per tonne

Premium gravel (specialty colours, slate): £90-£150 per tonne

For a typical 10 square metre driveway at 50mm depth, you need about 0.8 tonnes. With mid-range gravel at £75 per tonne, that’s £60 for materials.

Delivery charges range from £30-£80 depending on distance. Some suppliers offer free delivery over 5-10 tonnes.

Always request a quote including delivery. The cheapest price per tonne sometimes becomes expensive once delivery is added.

When to Hire a Professional

Complex driveways with curves, slopes, and drainage requirements need expertise.

Consider professional installation if:

• Your area exceeds 50 square metres
• You have significant drainage issues
• The slope is steeper than 1:12
• You need proper base preparation with MOT Type 1
• You’re uncertain about calculations

Professionals bring experience with ground preparation, edging installation, and proper compaction. They also have trade accounts with suppliers, sometimes offering better prices than retail.

The Royal Institution of Chartered Surveyors provides guidance on finding qualified contractors for groundworks and landscaping projects.

Environmental Considerations

Gravel is a permeable surface. Water drains through it, reducing runoff and helping prevent flooding.

This makes gravel driveways eligible for exemption from certain planning permissions under UK permitted development rules, unlike solid concrete or tarmac which may require drainage solutions.

Sustainable Gravel Choices

Recycled aggregates use construction waste instead of newly quarried stone. They’re cheaper and reduce environmental impact.

Local stone reduces transport emissions and often suits your regional aesthetic better.

The BRE Group provides environmental ratings for construction materials including aggregates, helping you make informed choices about sustainability.

Maintenance and Top-Up Calculations

Gravel migrates. Stones get kicked out, sink into soil, or distribute unevenly.

Expect to add a top-up layer every 2-4 years for driveways, less often for paths.

A maintenance top-up typically needs 20-30mm depth across the whole area. For a 20 square metre driveway:

20m² × 0.025m × 1.6 = 0.8 tonnes every 2-3 years

Budget for this ongoing cost when choosing gravel over solid surfaces.

Preventing Gravel Loss

Install proper edging. Metal, wooden, or plastic edging keeps stones contained.

Use a geotextile membrane underneath. This prevents gravel sinking into soil and reduces the amount that migrates away.

These additions reduce long-term maintenance needs and make your initial gravel order last longer.

Summary

Calculating gravel needs isn’t complicated once you understand the formula. Measure length, width, and depth in metres. Multiply them together for volume in cubic metres. Multiply by 1.6 to convert to tonnes.

Remember these key points:

Add 10-20% extra for uneven ground. Add another 10% for driveway compaction. Use minimum 50mm depth for driveways, 40mm for paths, and 30mm for decorative areas.

Choose stone size based on use. Smaller stones compact better for driveways. Larger stones work for visual impact in borders.

Account for delivery access and costs when planning your order. Sometimes multiple bulk bags are more practical than a loose load.

Round your final calculation up to the nearest half-tonne. Running short halfway through spreading costs more in time and extra delivery charges than ordering slightly too much initially.

Frequently Asked Questions

How much does a tonne of gravel cover?

One tonne of 20mm gravel covers approximately 10-12 square metres at 50mm depth. Coverage varies with stone size, larger stones cover less area because gaps between them are bigger.

Should I order gravel by volume or weight?

Weight (tonnes) is more accurate and preferred by UK suppliers. Gravel volume changes based on how tightly it’s packed, but weight remains constant. Always convert your volume calculations to tonnes for ordering.

Can I install gravel directly on soil?

You can, but it’s not recommended for driveways. The gravel will sink into the soil unevenly. Use a geotextile membrane and consider a MOT Type 1 base layer for load-bearing areas. Paths and decorative areas can go directly on firm, weed-free soil.

What’s the difference between gravel and shingle?

These terms are often used interchangeably in the UK. Technically, shingle refers to smooth, rounded stones typically 4-64mm, often found on beaches. Gravel is a broader term covering both rounded and angular stones. For buying purposes, they’re essentially the same thing.

How long does gravel last?

Gravel itself lasts indefinitely, it’s just stone. However, it migrates, sinks, and gets distributed unevenly over time. Most driveways need topping up every 2-4 years. Paths last longer, often 5-7 years before needing significant top-up. Proper edging and base preparation extend the lifespan significantly.