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Gravel CalculatorDriveway Cost Guide

Depth Guide

Recommended depths by project type and stone size

Bag to m² Converter

How much area will your bags of gravel cover?

Tonnes to Bags

Convert between tonnes, bulk bags, and small bags

MOT Type 1 Calculator

MOT Type 1 quantity with compaction allowance

Gravel for Driveways

Calculator pre-set for 50mm driveway depth

Gravel for Garden Paths

Calculator pre-set for 30mm path depth

Gravel for Patios

Calculator pre-set for 40mm patio depth

Gravel for Decorative Areas

Calculator pre-set for decorative borders

How Much Gravel?

Formula, worked examples, and depth guide

Driveway Cost Guide

Full 2026 cost breakdown — DIY vs professional

Gravel vs Alternatives

Gravel vs resin, tarmac, block paving, concrete

Planning Permission

The 5m² rule, SuDS 2025 changes, dropped kerbs

Best Gravel Types

Angular vs rounded, sizes, colours, and prices

How to Lay Gravel

Step-by-step from excavation to finished surface

Stop Gravel Spreading

7 proven containment methods

Gravel on a Slope

Gradient limits and retention techniques

Maintenance Guide

Seasonal upkeep, weed control, and top-ups

Cat-Proof Gravel

Stone selection and deterrents that work

Gravel vs Bark Mulch

Cost, lifespan, and which suits your borders

Wheelchair Access

Gravel grids and accessible surface design

Shop Gravel at Stones4GardensVisualise Gravel in Your Space

How Much Gravel Do I Need?

Enter your measurements below to get exact tonnage, bag counts, and live pricing. Then scroll down for UK depth recommendations, worked examples, and coverage tables — everything you need to order the right amount first time.

What are you covering?

Dimensions

1mWIDTH1mLENGTH5cmDEPTH
m
m
cm
This covers approximately 1 m² at 50mm depth. At this depth, one tonne covers ~11.1 m².

How Deep Should Gravel Be? (By Project)

Depth is the single biggest variable in how much gravel you need. Going from 30mm to 50mm increases your order by 67%. Most retailer calculators only offer three depth categories — here are nine, with the reasoning behind each.

Project TypeRecommended DepthNotes
Driveway (decorative layer)50 mmOn top of 100–150mm compacted MOT Type 1 sub-base
Garden path (foot traffic)30–40 mmThinner layer is adequate — no vehicle load
Patio area40 mmStable enough for garden furniture on compacted base
Decorative border / mulch30–40 mm40mm for weed suppression; 30mm if membrane underneath
Driveway on slope60–70 mmExtra depth at bottom to compensate for downhill migration
Self-binding gravel path50 mm (compacted)Compacts from loose; needs MOT Type 3 sub-base and water rolling
French drain / soakawayFull trench depthFills around the pipe; typically 300–600mm deep trenches
Sub-base (MOT Type 1)100–150 mm (loose)Compacts to ~80–120mm; separate from decorative surface
Shed base125 mm sub-base + 50 mm surfaceTotal build-up 175mm loose before compaction

Important: These depths are for the decorative finish layer only. Driveways, patios, and shed bases also need a compacted sub-base underneath — see our sub-base calculator for those quantities separately.

Gravel Coverage Reference Table (at 50mm Depth)

How much area does a tonne or a bulk bag cover? It depends on the bulk density of the stone. This table shows the numbers at the standard 50mm driveway depth — for other depths, adjust the calculator above.

Stone TypeDensity (kg/m³)kg per m²20kg bags per m²m² per tonnem² per 800kg bag
Slate gravel (20mm)1,500753.813.310.7
Golden gravel1,600804.012.510.0
Pea gravel1,55077.53.912.910.3
Grey granite1,600804.012.510.0
Pebbles / cobbles1,800904.511.18.9
Self-binding gravel1,700854.311.89.4
MOT Type 12,0001005.010.08.0

Densities are approximate bulk (loose pour) values. Actual weight varies with moisture content, grading, and supplier packing. Our calculator uses these verified densities — if your supplier quotes differently, adjust the result proportionally.

How We Calculate — The Formula

Every gravel calculator uses the same three-step formula. We publish ours so you can verify the numbers and adjust for your situation — something most retailer calculators don't do.

1

Measure the area (m²)

Rectangle: Length × Width
Circle: π × radius²
Triangle: 0.5 × base × height

2

Calculate volume (m³)

Area (m²) × Depth (m) = Volume (m³)
Convert depth from mm to metres: divide by 1,000. So 50mm = 0.05m.

3

Convert to weight (kg or tonnes)

Volume (m³) × Bulk Density (kg/m³) = Weight (kg)
Weight (kg) ÷ 1,000 = Weight (tonnes)
Bulk density varies by stone type — slate ≈ 1,500 kg/m³, granite ≈ 1,600 kg/m³, pebbles ≈ 1,800 kg/m³.

Step 4: Add Waste Allowance

Multiply the weight by your waste factor (1.05 for 5%, 1.10 for 10%, 1.20 for 20%). This accounts for compaction, spillage, uneven ground, and settling. Most projects benefit from at least 5–10%. The calculator above lets you set this directly.

5 Worked Examples (UK Homes)

Abstract formulas are useful, but real numbers are better. Here are five common UK projects with every calculation step shown.

1

Single-car driveway

Dimensions: 5m × 3m at 50mm depth · Stone: Slate gravel 20mm (1,500 kg/m³)

  1. 1.Area = 5 × 3 = 15 m²
  2. 2.Depth = 50mm ÷ 1,000 = 0.05 m
  3. 3.Volume = 15 × 0.05 = 0.75 m³
  4. 4.Weight = 0.75 × 1,500 = 1,125 kg (1.13 tonnes)
  5. 5.With 10% waste = 1,238 kg (1.24 tonnes)

Order: 2 × 500kg bulk bags, or 62 × 20kg bags

2

Garden path to the shed

Dimensions: 8m × 0.9m at 30mm depth · Stone: Golden gravel 20mm (1,600 kg/m³)

  1. 1.Area = 8 × 0.9 = 7.2 m²
  2. 2.Depth = 30mm ÷ 1,000 = 0.03 m
  3. 3.Volume = 7.2 × 0.03 = 0.216 m³
  4. 4.Weight = 0.216 × 1,600 = 346 kg (0.35 tonnes)
  5. 5.With 5% waste = 363 kg (0.36 tonnes)

Order: 19 × 20kg bags

3

Circular patio area

Dimensions: 4m diameter at 40mm depth · Stone: Pea gravel 10mm (1,550 kg/m³)

  1. 1.Radius = 4 ÷ 2 = 2 m
  2. 2.Area = π × 2² = 12.57 m²
  3. 3.Depth = 40mm ÷ 1,000 = 0.04 m
  4. 4.Volume = 12.57 × 0.04 = 0.503 m³
  5. 5.Weight = 0.503 × 1,550 = 779 kg (0.78 tonnes)
  6. 6.With 10% waste = 857 kg (0.86 tonnes)

Order: 1 × 800kg bulk bag + 3 × 20kg bags

4

Large decorative border

Dimensions: 12m × 1.5m at 40mm depth · Stone: Polished pebbles (1,800 kg/m³)

  1. 1.Area = 12 × 1.5 = 18 m²
  2. 2.Depth = 40mm ÷ 1,000 = 0.04 m
  3. 3.Volume = 18 × 0.04 = 0.72 m³
  4. 4.Weight = 0.72 × 1,800 = 1,296 kg (1.30 tonnes)
  5. 5.With 5% waste = 1,361 kg (1.36 tonnes)

Order: 1 × 1,000kg bulk bag + 19 × 20kg bags

5

Two-car driveway (large)

Dimensions: 10m × 5m at 50mm depth · Stone: Slate gravel 20mm (1,500 kg/m³)

  1. 1.Area = 10 × 5 = 50 m²
  2. 2.Depth = 50mm ÷ 1,000 = 0.05 m
  3. 3.Volume = 50 × 0.05 = 2.5 m³
  4. 4.Weight = 2.5 × 1,500 = 3,750 kg (3.75 tonnes)
  5. 5.With 10% waste = 4,125 kg (4.13 tonnes)

Order: 4 × 1,000kg bulk bags + 7 × 20kg bags

Waste & Compaction — Why You Always Need More

The raw calculation gives you the theoretical minimum. In practice, you'll always use more. Here's why, and how much extra to add.

Compaction & Settlement

Gravel settles by 10–15% in the first few weeks as stones interlock and fill air gaps. Angular stone settles less than rounded; slate less than pebbles. Most of this happens under foot or vehicle traffic.

Spillage & Spreading

Some gravel inevitably spills beyond the target area during installation. Without edging, migration into grass and borders is continuous. Even with edging, plan for 2–3% loss.

Uneven Ground

Real ground is never perfectly flat. Low spots consume extra depth, and you won't know exactly where they are until you're laying. A 50mm target depth might average 55mm across an uneven area.

What to Add

5% — clean rectangle, flat ground, solid edging.
10% — most domestic projects (our default recommendation).
20% — irregular shapes, slopes, soft ground, or no edging.

Why Weight Varies by Stone Type (Bulk Density)

A cubic metre of slate gravel weighs about 1,500 kg. A cubic metre of pebbles weighs about 1,800 kg. Same volume, 300 kg difference. That's because different stones have different bulk densities — the weight per unit volume when loosely poured, including the air gaps between stones.

Factors that affect bulk density include the mineral composition of the stone, how tightly the particles pack (angular slate stacks loosely; rounded pebbles pack more densely), moisture content, and the grading (mix of particle sizes). A well-graded aggregate with a range of sizes packs more densely than single-size stone.

This is why the calculator above asks which stone type you're using — not just the area and depth. Getting the density wrong by 300 kg/m³ on a 50m² driveway at 50mm depth means ordering 750 kg too much or too little. Our calculator uses verified densities for 13 UK gravel types.

20kg Bags vs Bulk Bags vs Loose Delivery

How you buy affects both cost and convenience. Here's a practical comparison for UK homeowners.

20kg Bags (Small Quantities)

Most expensive per kg, but practical for small projects (under 200kg), top-ups, and areas with no vehicle access for bulk delivery. Typically £3–£6 per bag. You can carry them through a house or down steps — sometimes the only option for rear gardens.

Bulk Bags (800–1,000kg)

The sweet spot for most domestic projects. Delivered by crane lorry or on a pallet. Price per kg is typically 40–60% lower than 20kg bags. Note: bulk bag weights vary by supplier — an “850kg” bag from one supplier might be “800kg” from another. Always check the stated weight before comparing prices.

Tipped / Loose Loads (4+ Tonnes)

Cheapest per tonne, but requires a minimum order (usually 4–10 tonnes) and vehicle access to tip directly onto your site. An 18-tonne rigid lorry needs firm, level ground and adequate width. Best for large driveways and new-build landscaping.

Rounding tip: Always round up to the next full unit. If you need 1,150 kg, order 2 × 800kg bulk bags rather than trying to split formats. The surplus is your future top-up supply. The calculator above shows optimised buy plans that minimise waste and cost.

Common Mistakes When Ordering Gravel

  • Confusing area with volume. Area (m²) is length × width. Volume (m³) includes depth. You need volume to calculate weight. A 15m² area at 50mm is only 0.75 m³ — not 15 m³.
  • Ignoring settlement. Gravel compacts by 10–15% in the first weeks. What looks like perfect coverage on day one will look thin by month two. Always add a waste allowance.
  • Using decorative depth for a sub-base role. A 50mm decorative layer won't stabilise a driveway on its own. You need 100–150mm of compacted MOT Type 1 beneath it. Budget for both layers separately.
  • Assuming all bulk bags weigh the same. They don't. “Bulk bag” can mean 750kg, 800kg, 850kg, or 1,000kg depending on the supplier. Compare by price per kg, not per bag.
  • Using “ton” instead of “tonne”. In the UK, gravel is sold in metric tonnes (1,000 kg). An imperial ton is 1,016 kg. The difference is small but compounds on large orders. UK suppliers quote in metric tonnes.
  • Ordering the wrong format for access. A crane lorry delivering bulk bags needs overhead clearance and firm ground. If your driveway is down a narrow path or behind a gate, 20kg bags may be the only practical option.

Circles, Triangles & Odd Shapes

Not every garden is a perfect rectangle. Here's how to handle irregular areas — and the calculator above supports all three shapes natively.

Circles

π × radius²

Measure the diameter across the widest point and halve it for the radius. Common for tree rings, circular patios, and round flower beds.

Triangles

0.5 × base × height

Common for corner sections, tapered borders, and areas where two paths meet at an angle. Measure the longest straight edge and the perpendicular distance to the opposite point.

Irregular Shapes

Split into simple shapes

Break the area into rectangles, triangles, and circles. Calculate each separately using our multi-area mode and add the results together. When in doubt, overestimate.

Frequently Asked Questions

How do I calculate how much gravel I need for a rectangular area?
Multiply length (m) × width (m) to get the area in m². Then multiply the area by the depth in metres (e.g. 50mm = 0.05m) to get volume in m³. Finally, multiply volume by the bulk density of your chosen stone (typically 1,500–1,800 kg/m³) to get the weight in kg. Divide by 1,000 for tonnes.
How do I work out gravel for a circular patio or tree ring?
Use π × radius² to get the area. If your circle is 3m across, the radius is 1.5m, so the area is π × 1.5² = 7.07 m². Then multiply by depth and density as usual. Our calculator above handles circles automatically — just switch to the circle shape.
What depth of gravel do I need for a driveway in the UK?
50mm (5cm) of decorative gravel on top of a compacted 100–150mm sub-base (MOT Type 1). The 50mm figure is for the finish layer only — the sub-base is a separate calculation. Going thinner than 50mm exposes the membrane within weeks, especially under turning wheels.
Is 50mm gravel depth enough? When should it be deeper?
50mm is the standard for driveways and most paths. Go deeper (60–70mm) for sloped areas where gravel migrates downhill, soft ground, or areas with heavy vehicle traffic. For decorative borders, 30–40mm is adequate if a weed membrane is used underneath.
How many 20kg bags of gravel per square metre?
At 50mm depth with a typical density of 1,500 kg/m³: 0.05 × 1,500 = 75 kg per m², which is about 4 bags of 20kg. At 30mm depth it drops to about 2.3 bags. The exact number varies by stone type — denser stones like granite need more bags per m².
How many square metres does a bulk bag of gravel cover?
A standard 800kg bulk bag of 1,500 kg/m³ gravel covers approximately 10.7 m² at 50mm depth, or 17.8 m² at 30mm depth. At 1,800 kg/m³ (pebbles), the same 800kg covers about 8.9 m² at 50mm. Always check your supplier's bulk bag weight — some are 850kg or 1,000kg.
Why does the weight change for the same volume of gravel?
Because different stones have different bulk densities. A cubic metre of slate gravel weighs around 1,500 kg, while the same volume of granite weighs about 1,600 kg and pebbles weigh around 1,800 kg. Moisture content, grading, and how loosely the stone is packed also affect weight.
Should I add extra gravel for compaction and waste?
Yes. Adding 5–10% for a straightforward rectangular area is standard practice. For irregular shapes, sloped ground, or areas where gravel will spill during installation, 10–20% is more realistic. Our calculator lets you set 0%, 5%, 10%, or 20% waste allowance.
What is the difference between a tonne and a bulk bag?
A tonne is exactly 1,000 kg. A bulk bag (also called a dumpy bag or jumbo bag) varies by supplier — typically 800–1,000 kg. Never assume a bulk bag is a full tonne. When comparing prices, always check the bag weight and compare price per kg, not per bag.
Do I need MOT Type 1 before decorative gravel on a driveway?
Yes. A compacted sub-base of at least 100mm MOT Type 1 is essential for any area with vehicle traffic. Without it, gravel sinks into soft ground and develops ruts. For paths and decorative areas without traffic, you can skip the sub-base and lay directly on compacted earth with a membrane.
How much gravel do I need for a French drain trench?
Calculate the trench volume (length × width × depth in metres), then subtract the volume of any drainage pipe inside. For a 10m trench that is 300mm wide and 600mm deep with a 100mm pipe: trench volume = 10 × 0.3 × 0.6 = 1.8 m³, pipe volume ≈ 0.08 m³, gravel needed ≈ 1.72 m³. Our French drain calculator does this automatically.
Can I use the same depth for pea gravel and slate chippings?
Generally yes — the depth depends on the project type, not the stone. However, pea gravel's rounded shape means it settles more and shifts underfoot, so you may want 5–10mm extra depth to compensate. Slate's angular shape locks together and holds depth better.
How accurate is an online gravel calculator?
A good calculator gives an estimate within 5–10% for regular shapes on flat ground. Accuracy depends on measurement precision, the bulk density assumed, and ground conditions. We show our assumptions (density per stone type, waste %) so you can adjust for your situation. Always round up when ordering — returning surplus is easier than reordering a shortfall.
Can I convert feet and inches to work out tonnes?
Yes. Convert feet to metres (1 foot = 0.3048m) and inches to metres (1 inch = 0.0254m), then use the same formula: area (m²) × depth (m) × density (kg/m³) = weight (kg). Our calculator has a built-in imperial toggle that handles this conversion for you.
Do I need a weed membrane? Does it change how much gravel I buy?
A weed membrane doesn't change the amount of gravel — it sits flat beneath the stone and takes up negligible thickness. However, it dramatically reduces ongoing maintenance. For any decorative or path application, a heavy-duty woven membrane is strongly recommended.
What if my area is sloped or uneven?
Gravel naturally migrates downhill on slopes. Add 10–20% extra material to account for this, and use a deeper layer (60–70mm) at the bottom of the slope where gravel accumulates. Gravel grids can help hold stone in place on gradients up to about 1:10.
How much gravel for a path versus a driveway?
A path typically needs 30mm depth (foot traffic only), while a driveway needs 50mm (vehicle traffic). For a 10m × 1m path at 30mm you need about 0.45 tonnes of standard gravel. The same dimensions as a driveway at 50mm would need about 0.75 tonnes — roughly 65% more material.
Why is rockery stone not in standard calculators?
Rockery stone and boulders are placed individually rather than spread to a uniform depth, so a standard area × depth formula doesn't apply. Coverage depends on stone size, how closely they're packed, and the visual effect you want. For rockery projects, contact a supplier directly for advice.
How much does gravel cost per m² in the UK?
For the gravel alone at 50mm depth: £3–£5/m² for standard types (golden gravel, pea gravel), £5–£8/m² for premium types (granite, slate), and £8–£12/m² for luxury options (Polar Ice, marble chippings). These figures don't include sub-base, membrane, edging, or labour.
How do I calculate gravel for a triangular area?
Area = 0.5 × base × height. Then multiply by depth and density as for any other shape. For example, a triangle with a 4m base and 3m height: area = 0.5 × 4 × 3 = 6 m². At 50mm depth and 1,500 kg/m³: 6 × 0.05 × 1,500 = 450 kg (0.45 tonnes).
What is the cheapest way to buy gravel in the UK?
Buy in bulk. Tipped loads (loose delivery) are the cheapest per tonne but require minimum orders (usually 4+ tonnes) and space for the lorry. Bulk bags (800–1,000kg) are the next best value. 20kg bags are the most expensive per kg but useful for small areas and top-ups where delivery of bulk isn't practical.

Related Tools & Guides

Everything you need to plan your gravel project

Gravel Depth Guide

Interactive depth table for every project type

MOT Type 1 Calculator

MOT Type 1 quantities for driveways and patios

Bag Converter

Convert between bags, tonnes, and coverage area

Driveway Calculator

Pre-set for 50mm depth with driveway-specific advice

Best Gravel for Driveways

Types, sizes, and colour recommendations for UK driveways

How to Lay Gravel

Step-by-step from excavation to finished surface

About Our Methodology

This calculator and guide use verified bulk densities for 13 UK gravel types, sourced from supplier technical data sheets and cross-referenced against British Standards BS EN 1097-3 (bulk density of aggregates). Depth recommendations follow standard UK landscaping practice for domestic projects. Our waste allowances (5%, 10%, 20%) are based on typical domestic installation scenarios. This page was last reviewed in April 2026.

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