Gravel and Aggregate Quantity Calculator: Tonnes per M2 by Depth and Material Type

Quick Answer: Most decorative and construction aggregates have a bulk density of approximately 1.5–1.8 tonnes per cubic metre. A 50 mm depth of gravel covers approximately 12 m² per tonne; 100 mm depth covers approximately 6 m² per tonne. MOT Type 1 sub-base at 100 mm depth covers approximately 5 m² per tonne due to higher density. Add 5–10% for compaction loss on sub-base layers; standard waste allowance for decorative gravel is 5%.

Summary

Aggregate quantities form the silent half of most groundworks calculations. Order too little and you get a part-finished job and an emergency tipper run; order too much and the customer pays for material left rotting on the verge for weeks. The maths is unforgiving — a 50 m² driveway at 50 mm decorative gravel needs roughly 4 tonnes; getting that right within 10% saves £40–£80 per overordered tonne and a delayed start.

The starting point is bulk density: gravel, MOT Type 1, screened topsoil and sand all have specific densities, and the figure shifts whether the material is in supplier "loose tipped" or compacted in place. Typical UK decorative gravels (10 mm, 20 mm round) have loose density 1.5 t/m³; angular crushed stone is 1.6–1.7 t/m³; MOT Type 1 sub-base (well-graded crushed limestone or granite) is 1.8 t/m³ loose, 2.0+ t/m³ compacted. Apply the right density for the material and the calculation works out almost exactly.

For owners and homeowners, the relevant figures are how many tonnes for a path or driveway, what's the cost, and what depth to specify. This article gives the working figures and the reasoning behind them so the right amount can be ordered first time.

Key Facts

• Bulk density (loose, decorative gravel) — 1.5 tonnes per m³ (10 mm, 20 mm round/angular).
• Bulk density (MOT Type 1, loose) — 1.8 tonnes per m³.
• Bulk density (MOT Type 1, compacted) — 2.0+ tonnes per m³.
• Bulk density (screened topsoil) — 1.0–1.4 tonnes per m³ depending on moisture.
• Bulk density (sharp/concrete sand) — 1.5 tonnes per m³.
• Bulk density (building/soft sand) — 1.4 tonnes per m³.
• Bulk density (ballast — sand and gravel mix) — 1.7 tonnes per m³.
• Bulk density (rounded river gravel, washed) — 1.5 tonnes per m³.
• Bulk density (limestone chippings) — 1.6 tonnes per m³.
• Bulk density (granite chippings) — 1.7 tonnes per m³.
• Compaction loss — typical 8–15% volume reduction when MOT Type 1 is compacted; allow 10% extra material for sub-base.
• Waste allowance — 5% for decorative gravel; 10% for sub-base on uneven or sloping sites.
• Bulk bag — typically 800–900 kg (NOT 1 tonne); often called "1-tonne bag" but underweight.
• Loose tip delivery — 1, 5, 10, 20-tonne loads typical; 20-tonne lorry minimum on rural delivery.
• Highway road specification — Type 1 must conform to Highways Specification SHW Series 800 / Clause 803.
• DIY / driveway gravel — typically 6 mm or 10 mm pea gravel, 20 mm cotswold, or 14 mm Plum slate.
• Sub-base depth (drives) — typical 100–150 mm of MOT Type 1 + 30–50 mm decorative top.
• Path sub-base depth — typical 75–100 mm of MOT Type 1 + 30–50 mm decorative top.

Quick Reference Table

Detailed Guidance

Calculation method

Standard formula:

Tonnes = Area (m²) × Depth (m) × Bulk Density (t/m³)

Worked example: 60 m² driveway, 100 mm sub-base + 40 mm decorative.

Sub-base:

• 60 m² × 0.100 m × 1.8 t/m³ = 10.8 m³ × 1.8 = 10.8 tonnes loose
• With 10% compaction: 10.8 × 1.10 = 11.9 tonnes ordered
• Round to delivery: 12 tonnes

Decorative top:

• 60 m² × 0.040 m × 1.5 t/m³ = 2.4 m³ × 1.5 = 3.6 tonnes loose
• With 5% waste: 3.6 × 1.05 = 3.78 tonnes
• Round to delivery: 4 tonnes (or 5 × 800 kg bulk bags = 4 tonnes equivalent)

Total: 12 t MOT Type 1 + 4 t decorative = 16 tonnes.

Bulk density variations

Different aggregates have different bulk densities:

• Loose density — material as delivered, in a heap, with air spaces.
• Compacted density — after compaction with a vibrating roller or whacker plate; air spaces reduced.
• In-situ density — settled but not compacted (typical of decorative gravel a year after laying).

For ordering, use loose density and add a compaction allowance (8–15% extra) for sub-base layers that will be compacted. Decorative top layers are not compacted, so loose density is the order figure.

Material selection — driveways

MOT Type 1 — the standard sub-base. Crushed limestone or granite, well-graded particles 0–63 mm. Compacts to load-bearing level. Use 100 mm minimum for vehicle traffic, 150 mm for soft soils.

MOT Type 3 — open-graded; used where drainage is critical (SuDS-compliant driveways).

Decorative top layer:

• 10 mm pea gravel — economical, sweeping required regularly to keep moss and weeds clear.
• 20 mm angular crushed stone — better for vehicle drives; less migration.
• 14–20 mm slate chippings — premium look; durable, low maintenance.
• 20 mm Cotswold gravel — pale buff; popular but premium price.

Material selection — paths

Limestone fines (decomposed limestone, "Crushed and run") — bonds when wetted; firm path surface; no membrane needed.

Self-binding gravel — graded mix; bonds with rolling; rural-feel paths.

Loose decorative gravel — needs edging to retain; aesthetic but requires regular topping.

Sub-base depth selection

Compaction and laying technique

For sub-base:

• Lay in 50 mm layers (lifts).
• Compact each lift with a vibrating plate (whacker plate for paths; tracked roller for driveways).
• Final compacted thickness as per design (e.g. 100 mm laid in 2 × 50 mm lifts).
• Wet lightly between lifts to assist compaction.

For decorative top:

• Spread with rake to even thickness.
• No compaction needed for loose decorative gravel.
• Edging restraint essential to prevent migration.

Edging and restraint

Loose gravel migrates without edging. Options:

• Treated timber edging (£8–£15/m).
• Concrete kerb (£12–£25/m).
• Steel edging (£18–£35/m).
• Recycled plastic edging (£10–£18/m).
• Block paving or brick course (£20–£50/m).

For driveways, kerb or block paving edge is standard. For paths, timber or steel is sufficient.

Membranes — geotextile and weed barriers

Beneath sub-base:

• Geotextile (Terram, Bidim) — 100 g/m² for paths, 150 g/m² for driveways. Separates sub-base from soft soil; prevents pumping of fines.

Between sub-base and decorative top:

• Weed-suppressant membrane — needle-punched non-woven 100–150 g/m².
• Allows water through; blocks weed germination.

Both contribute to sub-base longevity and reduce the depth of decorative gravel needed (without membrane, gravel migrates into sub-base over years).

Material costs (2026 reference)

Typical UK delivered prices (vary by region):

• MOT Type 1 — £20–£40 per tonne loose tipped; £55–£85 per bulk bag.
• Sharp sand — £25–£45 per tonne loose; £50–£70 per bulk bag.
• 10 mm pea gravel — £40–£70 per tonne; £55–£85 per bulk bag.
• 20 mm Cotswold — £75–£140 per tonne; £85–£120 per bulk bag.
• Slate chippings — £80–£150 per tonne.
• Granite chippings — £45–£80 per tonne.

Delivery typically £40–£80 minimum charge for small loads; free over 10 tonnes within typical local radius.

Permeable paving and SuDS

Where front gardens exceed 5 m² of impermeable surface, planning permission or permeable paving solutions are required (Town and Country Planning (General Permitted Development) Order 2008 amendments).

SuDS-compliant driveway construction:

• 100 mm MOT Type 3 (open-graded) sub-base.
• 50 mm sharp sand laying course.
• Permeable block paving or open-jointed pavers.
• Decorative gravel allowable if within a contained, well-draining structure.

For traditional construction with non-permeable surfacing (concrete, asphalt), a soakaway or rainwater management plan is required.

Worked example — small front driveway

Job: 30 m² front driveway, replacing existing tarmac.

Sub-base preparation:

• Excavate 200 mm deep (allow for sub-base + decorative top + lift).
• Geotextile membrane over compacted soil (100 g/m² × 30 m² = 30 m²).
• 100 mm MOT Type 1: 30 × 0.10 × 1.8 = 5.4 tonnes loose; with 10% compaction = 5.94 t; round to 6 tonnes.
• Compact with whacker plate in 50 mm lifts.
• 40 mm decorative gravel (20 mm Cotswold): 30 × 0.04 × 1.5 = 1.8 tonnes; with 5% waste = 1.89 t; round to 2 tonnes.

Total: 6 t MOT 1 + 2 t Cotswold + 30 m² geotextile + edging.

Consumer-facing question — "how do I work out gravel for my path?"

For a typical garden path 10 m long × 1 m wide × 50 mm decorative gravel:

• Area: 10 m²
• Volume: 10 × 0.05 = 0.5 m³
• Density: 1.5 t/m³ (typical decorative)
• Tonnes: 0.5 × 1.5 = 0.75 t
• Plus 5% waste: 0.79 t
• Round up: 1 tonne (or 1 × 800 kg bulk bag + a top-up)

For sub-base under the path (75 mm MOT Type 1):

• 10 × 0.075 × 1.8 = 1.35 t loose
• With 10% compaction: 1.49 t
• Round to: 1.5 tonnes

Total: 1 t decorative + 1.5 t sub-base + 10 m² of geotextile membrane.

Frequently Asked Questions

How much gravel do I need for 1 square metre at 50 mm deep?

Approximately 75 kg or 0.075 tonnes for typical decorative gravel (1.5 t/m³). At 100 mm depth, 150 kg.

What's the difference between a "tonne" and a "bulk bag"?

A bulk bag (FIBC, "tonne bag") in the UK aggregates trade is typically 800–900 kg, NOT 1,000 kg. Loose tipped delivery is sold by weight on the load.

Does MOT Type 1 need to be compacted?

Yes — for any load-bearing application. Without compaction, MOT Type 1 settles unevenly and tracks as vehicles drive over it.

Can I use building sand instead of sharp sand under paving?

No — building sand is too fine and doesn't drain. Use sharp sand (30 mm depth) as the laying course beneath block paving or natural stone.

What gravel is best for a driveway?

20 mm angular crushed stone or slate. Avoid 10 mm pea gravel for driveways — it migrates and sinks into the sub-base.

Do I need a membrane?

Yes — geotextile separation membrane between soil and sub-base prevents pumping. Weed membrane between sub-base and decorative top reduces weed growth and slows gravel migration.

How much waste should I allow?

5% for decorative gravel on a defined area; 10% for sub-base on an uneven or sloping site; 15% if cutting around features (kerb stones, drains).

Regulations & Standards

• Building Regulations 2010 — Approved Document H (drainage and waste disposal); SuDS requirements for new driveways.

• Town and Country Planning (General Permitted Development) Order 2008 — front garden permitted development for permeable surfaces.

• Highway Construction Specification — SHW Series 800 / Clause 803 — MOT Type 1 specification.

• BS EN 13242 — Aggregates for unbound and hydraulically bound materials.

• BS EN 13285 — Specification for unbound mixtures.

• Highway Authorities and Utilities Committee (HAUC) Specification — for highway approach work.

• Highways England SHW Series 800 — material specification for sub-base materials.

• BSI — BS EN 13242 Aggregates — material standard.

• Mineral Products Association — UK aggregates trade body.

• SuDS Manual (CIRIA C753) — sustainable drainage systems guidance.

• concrete volume calculator — companion calculator for foundations and slabs.

• concrete mix ratios — appropriate mix selection.

• concrete driveway pricing — alternative driveway construction.

• artificial grass pricing — sub-base requirements — uses comparable sub-base specifications.