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Gravel depth is the quiet variable behind every estimate. Half an inch too much over a driveway is tons of extra stone; an inch too little in a bed and the fabric shows through within a season. Here is the depth to use for each kind of project, why it differs, and how stone size changes the answer.
Gravel depth chart by project
| Project | Depth | Stone | Why |
|---|---|---|---|
| Decorative bed (over fabric) | 2″ | Pea gravel, 3/4″ chips | Just enough to hide fabric; deeper wastes money and buries plants |
| Decorative bed (no fabric) | 3″ | Same | Extra inch compensates for stone sinking into soil |
| Beds with 1–3″ river rock | 3–4″ | River rock | Must be 1.5–2× the largest stone |
| Garden path (foot traffic) | 3″ | Pea gravel or 3/8″ crushed | Comfortable to walk on, stays put with edging |
| Hard-surface path | 3″ base + 1″ top | Crusher run + stone dust | Compacts into a firm, wheelchair-friendly surface |
| Gravel patio | 2–3″ base + 2″ top | Crusher run + pea gravel | Base stops furniture sinking; thin top stays walkable |
| Shed / hot tub / AC pad | 4–6″ | #57 clean stone | Drains, stays level under load |
| Driveway (new, firm soil) | 4″ base + 2–3″ top | Crusher run + 3/4″ | Minimum that will carry cars without rutting |
| Driveway (clay / heavy use) | 8–12″ in 3 layers | #3 + crusher run + 3/4″ | Spreads load over weak subgrade |
| Driveway top-up | 2″ | 3/4″ crushed | Replaces what has migrated or sunk |
| Under a concrete slab | 4–6″ | #57 or crusher run | Capillary break and uniform support (check local code) |
| French drain | Full trench, 2″ over pipe | Washed 3/4″–1 1/2″ | Maximises water storage; no fines to clog |
| Behind a retaining wall | 12″ wide zone | #57 washed | Drainage – depth here is horizontal |
| Play area | 9–12″ | Pea gravel | Fall-protection depth per playground guidance |
Pick a project depth from the chart, enter your area and see exactly how many tons it comes to.
Rule 1: depth follows stone size
A layer should be at least 1.5 to 2 times the largest stone, otherwise stones sit in a single layer with gaps that show the ground beneath. Pea gravel (3/8″) is fine at 2″; 3/4″ stone needs 2–3″; 1–3″ river rock needs 3–4″; 3–5″ rock needs 5–6″. Larger decorative cobbles are placed as a single layer rather than poured to a depth.
Rule 2: structural layers are measured compacted
When a spec says a 6″ base, it means 6″ after compaction. Dense-graded stone such as crusher run loses 15–20% of its volume under a plate compactor, so you spread about 7–7.5″ loose to end up with 6″. Our calculators have a compaction allowance for exactly this. Clean stone (#57) barely compacts – 5–10% is plenty.
Rule 3: thin for looks, thick for loads
Depth is doing two different jobs. In a decorative bed it only has to hide the soil, so more depth buys nothing but a bigger bill and plants that struggle to push through. Under a driveway or slab, depth spreads the load across weak soil – which is why the right answer depends on your subgrade: 4″ is enough on well-drained sandy gravel, while heavy clay that goes soft when wet may need 8–12″ to stop rutting.
What goes wrong when gravel is too shallow
- Landscape fabric or soil shows through within weeks as stone shifts.
- Weeds root through the thin layer.
- Driveways rut and develop potholes because the load reaches the soil.
- Pads for sheds and hot tubs settle unevenly.
What goes wrong when gravel is too deep
- Pea gravel over 3–4″ becomes exhausting to walk on and furniture legs sink.
- Decorative beds smother shallow-rooted plants and bury edging.
- Loose top layers on driveways push into drifts under tires; keep the top layer at 2–3″ over a compacted base.
- Cost – every extra inch over 500 sq ft is about 2 tons of stone.
How to measure depth on site
Drive a few stakes around the area and mark the finished height with a string line, then measure down to the ground at several points – the average is your depth. On uneven ground the average is almost always deeper than you guessed, which is another reason to order a small margin. For driveways, set the string with a slight crown (about 1/4″ per foot from the centre) so water runs off.
Frequently asked questions
How deep should gravel be for a driveway?
A new driveway needs 8–12 inches total in layers – a 4–6″ compacted crusher-run base with a 2–3″ top layer of 3/4″ stone, plus a sub-base on soft clay. An existing driveway only needs a 2″ top-up.
How deep should gravel be for a walkway?
3 inches of pea gravel or small crushed stone, with edging. For a firm, accessible path use 3″ of compacted crusher run topped with 1″ of stone dust.
How deep should decorative gravel be?
2 inches over landscape fabric for pea gravel and 3/4″ chips; 3 inches if you skip the fabric or use larger 1–3″ rock.
How deep should gravel be under a shed?
4–6 inches of compacted #57 (3/4″ clean) stone, extending 12″ beyond the shed on each side so roof runoff drains into stone rather than soil.
How deep should gravel be under a concrete slab?
Most residential codes call for 4 inches of compacted granular base; 6″ is common on clay. Always check your local building code and the slab designer’s spec.
