Grade and size are two different things
A single supplier may sell crushed limestone, pea gravel, river rock and MOT Type 1 sub-base, all under the loose word “gravel”. Grades such as Type 1 or Type 4 come from a specification and describe how a material is made and what it is used for. Sizes such as “10 mm” or “20 mm” describe only how big the particles are. Both matter when you choose a stone.
Understanding the two together is what tells you whether a bag is a decorative surface or a structural layer that will be buried under something else.
How gravel is sized
Size means nominal particle size in millimetres. Aggregate is graded by passing it over a series of screens or sieves, so a 20 mm gravel is the material that mostly passes a 20 mm screen but not a smaller one. Because real particles vary, a grade is a range rather than one exact size.
Sizing matters for two reasons. The stone has to be small enough to spread and bed down neatly, but large enough to drain and lock together under load. A layer that is thinner than the stone itself will not cover evenly, and larger aggregate generally needs more depth to interlock.
Common gravel sizes and where they are used
| Size | Typical use | Notes |
|---|---|---|
| 4–10 mm | Decorative beds, between paving joints, small paths | Fine, neat finish |
| 10–14 mm | Paths and decorative borders | Common all-round size |
| 14–20 mm | Driveway surfaces, general landscaping | Good balance of looks and grip |
| 20–40 mm | Larger beds, drainage, rough ground | More open, fewer stones per area |
| MOT Type 1 / 2 / 4 | Sub-base and fill layers | Structural, not decorative surfaces |
There is no single standard size. The right grade depends on the surface you want, the volume of water it must drain and the load it has to carry.
Sub-base gravel: Type 1, Type 2 and Type 4
UK MOT sub-base grades describe the compacted layer that carries a surface. Type 1 is well graded and contains enough fine material to compact into a firm, dense base — the default beneath driveways, patios and paths. Type 2 has a more open, coarser grading with fewer fines: it drains more freely but does not compact as firmly, so it suits areas where water movement matters more than a hard finish. Type 4 is a coarser capping or fill material used lower in the build-up; it is cheap bulk fill but not a firm finish on its own.
What gravel is best for each job
| Job | Typical choice |
|---|---|
| Driveway surface | 14–20 mm crushed stone |
| Garden path or play area | Pea gravel or smooth 10 mm |
| Decorative bed | 10–20 mm decorative gravel or pebbles |
| Base under paving or a driveway | MOT Type 1 |
Choose the stone that suits the load, the drainage and the look you want. A driveway needs a stone that grips and drains; a play area should be smooth and rounded; a decorative bed is judged on appearance.
Cheapest types of gravel
Cost follows processing. Crushed stone, crushed concrete and other recycled aggregates are usually the cheapest, because they are produced in bulk from local rock or reclaimed material. Decorative stones — polished pebbles, coloured gravels and imported stone — cost the most because of sorting, washing and transport.
For a base layer a cheap crushed sub-base is usually the right choice. For a visible surface the cheapest stone is not always the best value, because appearance and durability matter more than the price per bag.
Gravel types FAQ
Quick answers on grades, sizes and choosing a material.
What is type 4 gravel?
Type 4 (MOT Type 4) is a coarse, well-graded granular fill used as a capping or lower sub-base layer in the UK. It is cheaper bulk fill, but it does not compact to a firm finish, so it is normally covered by a Type 1 base and then a surface layer.
What is the standard size of gravel?
There is no single standard size. Common graded sizes are 4–10 mm, 10–14 mm, 14–20 mm and 20–40 mm. Roughly 10 mm and 14–20 mm are the most common for paths and driveways, while 20–40 mm suits larger coverage and drainage.
What gravel is best?
It depends on the job. Crushed stone around 14–20 mm is best for driveway surfaces, pea gravel for paths, play areas and decorative beds, and MOT Type 1 for the compacted base layer under pavers, patios and driveways.
What is type 1 gravel used for?
MOT Type 1 is a sub-base material. It is laid as the compacted base layer under driveways, patios, paths and shed bases, spread in layers and compacted before the finishing surface goes on top.
What's the difference between type 1 and type 2 gravel?
Type 1 is well graded and holds more fine material, so it compacts into a firm, dense, interlocking sub-base. Type 2 has a more open, coarser grading with fewer fines, so it drains more freely but does not compact as firmly. Use Type 2 where drainage matters more than a hard finish.
How do you size gravel?
Gravel is sized by its nominal particle size in millimetres, sorted by passing the material over screens or sieves. A 20 mm gravel mostly passes a 20 mm screen. The grade you choose depends on the surface you want and the load it has to carry.
What size gravel should I use?
Use about 10 mm for paths and small decorative areas, 14–20 mm for driveway surfaces, 20–40 mm for larger beds and drainage, and MOT Type 1 for any compacted base layer.
What is the cheapest type of gravel?
Crushed stone, crushed concrete and other recycled aggregates are usually the cheapest, because they need less processing than decorative stone. Polished pebbles and specialty decorative gravels cost the most.
Grades and ranges vary by supplier and region. Confirm the exact material, size and specification with your supplier before ordering.