Hardscape · Guide
Paver Base Depth: How Much Gravel and Sand Goes Under a Patio
A paver patio lasts as long as its base. Here is how deep each layer should be, why, and how to turn those depths into tons of gravel and a pile of soil to get rid of.
When a paver patio fails, it fails from underneath. Pavers sink in the middle, tip at the edges, or heave after a hard winter, and in every case the cause is below the surface. The pavers themselves almost never break.
So the most important decisions on a paving job are about material nobody will see: how deep the base is, what it is made of, and how well it is compacted.
The layers, from the top down
Pavers. Concrete pavers for patios and paths are usually 2⅜ inches (60 mm) thick. Driveway pavers are 3⅛ inches (80 mm).
Bedding sand. One inch of coarse sand, screeded flat. Its only job is to give the pavers a smooth bed to settle into. It is not there to fix an uneven base.
Gravel base. The structural layer. Compacted crushed stone that spreads the load and lets water drain away.
Geotextile fabric. Optional on sandy soil, strongly advised on clay. It stops the base stone from being pressed down into soft soil and the soil from pumping up into the stone.
Subsoil. Whatever is there once the topsoil has been removed. It needs to be firm, and compacted if it has been disturbed.
How deep should the base be?
The right depth depends on what will go over the paving, what the soil is like, and how hard the ground freezes.
| Use | Well-drained soil, mild climate | Clay soil or hard frost |
|---|---|---|
| Garden path, foot traffic | 4 in (10 cm) | 6 in (15 cm) |
| Patio | 4 to 6 in (10 to 15 cm) | 6 to 8 in (15 to 20 cm) |
| Driveway, cars | 8 in (20 cm) | 10 to 12 in (25 to 30 cm) |
These are typical figures from paver makers’ installation guides. If your pavers came with a guide, follow it. And if you are unsure which column you are in, use the deeper one. Extra base costs a little more gravel and digging. Too little cannot be fixed without lifting the whole patio.
Clay needs more base because it holds water, and wet clay is soft. Frost needs more base because water in the ground expands when it freezes and lifts whatever is above it. A thick, free-draining base keeps water away from the underside of the paving.
What to use for the base
Ask for one of these, depending on what your local yard calls it:
- Crusher run
- Road base or dense graded aggregate
- ¾ inch minus (crushed stone from three quarters of an inch down to dust)
- Paver base
They are all the same idea: angular crushed stone in a range of sizes, including fine particles. The mix of sizes is what lets it lock together into something close to solid when compacted.
Do not use rounded gravel such as pea gravel or river rock. Round stones roll against each other and never lock. Do not use sand alone, which shifts and washes out.
What to use for the bedding layer
Coarse, sharp sand, sold as concrete sand or bedding sand. The grains are angular and of mixed sizes, so they hold their place.
Avoid fine mason sand or play sand, which is too soft and stays mobile. Opinions differ on stone dust, also called screenings. Some installers like it, but it holds water and can stay soft, and most paver makers specify concrete sand.
Keep the bedding layer to 1 inch. A thicker bed does not make a stronger patio. It makes a softer one.
How deep to dig
Add the layers together:
For a patio with a 6 inch base: 6 + 1 + 2⅜ = 9⅜ inches below the finished surface. If the finished patio should sit level with the lawn, that is how far down you dig. If it should sit an inch proud of the lawn, dig an inch less.
Dig the hole wider than the patio as well, by about 6 inches on every side. The edge restraint needs compacted base under it, or the outer row of pavers will tip outward.
And build in a slope. A patio should fall away from the house by about an eighth to a quarter of an inch per foot, which is a 1 to 2% grade. Set that slope in the subsoil, so that every layer above it is an even thickness.
Working out the quantities
Take a patio 16 feet by 12 feet on clay, with a 6 inch base.
Base gravel. The base covers the patio plus 6 inches all around, so 17 feet by 13 feet.
- Area: 17 × 13 = 221 sq ft
- Compacted volume: 221 × 6 ÷ 12 = 110.5 cu ft
- Loose volume to order, with 15% for compaction: 127 cu ft, or 4.7 cu yd
- Weight at 1.4 tons per yard: about 6.6 tons
Bedding sand. Under the pavers only.
- Area: 16 × 12 = 192 sq ft
- Volume: 192 × 1 ÷ 12 = 16 cu ft
- With 10% allowance: 17.6 cu ft, or 0.65 cu yd
- Weight at 1.35 tons per yard: about 0.9 tons
The paver patio calculator does all of this, along with the paver count and the edging.
The part everyone forgets: the spoil
Every cubic foot of base and sand that goes in replaces a cubic foot of soil that has to come out. And soil takes up more room once it has been dug, because digging loosens it. This is called bulking, and for ordinary garden soil it adds about 25 to 30%.
For the same patio:
- Hole: 221 sq ft × 9⅜ in ÷ 12 = 173 cu ft, or 6.4 cu yd in the ground
- After bulking by 25%: about 8 cubic yards of loose soil
Eight cubic yards is a pile the size of a small car, and it weighs eight to ten tons. Decide where it is going before you start digging. Some can fill low spots in the garden or build up a bed. The rest needs a dumpster rated for soil, or a hauler. It is often the single largest hidden cost of a patio.
Compaction: the step that makes the base work
Uncompacted base is just a pile of gravel. Compacted, the same material carries a car.
- Rent a plate compactor. A hand tamper is fine for a small path. For a patio, the machine is worth every dollar.
- Compact the subsoil first. One or two passes over the bottom of the hole.
- Add the base in layers. No more than about 3 to 4 inches of loose stone at a time. A plate compactor cannot reach deeper than that, and a thick layer stays loose at the bottom.
- Dampen it. Slightly moist stone compacts far better than dry. A light spray from a hose is enough.
- Make several passes in different directions, until the plate bounces on the surface instead of sinking in.
A 6 inch base therefore goes in as two layers, each compacted before the next is added. The 15% compaction allowance in the calculator is what this process takes out of the loose volume.
Common mistakes
- Laying on sand over soil, with no base. It looks fine for a season. Then it settles unevenly and weeds come up through every joint.
- Leaving topsoil underneath. Topsoil is full of organic matter that rots and shrinks. Dig down to firm subsoil.
- Compacting the full depth in one go. The top is hard and the bottom is loose. Always compact in layers.
- Using the bedding sand to correct levels. If the base has a dip, fill the dip with base and compact it. Thick sand settles.
- Stopping the base at the edge of the pavers. The edging then sits on soil and the border fails first.
- No slope. Water stands on the surface, soaks into the joints, and freezes.
Get the base right and the visible part of the job, laying the pavers, is the easy and satisfying afternoon at the end.
Written and checked by Bertha
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