A gravel driveway is not one layer of stone but two: a coarse base that carries the weight of your cars, and a finer top layer that gives the finished surface. That is why the maths for a driveway is two quick calculations rather than one — you work out each layer on its own, then add the two together. Get the depths right and the rest is simple area-times-depth arithmetic.
This guide walks through both layers step by step, with a full worked example and a table of totals for common driveway sizes. If you would rather skip the arithmetic, the free Gravel Calculator does it for you: enter the length, width and depth of one layer at a time and it returns cubic yards and tons.
The two layers of a gravel driveway
Each layer does a different job, and they use different stone. Getting the split right matters more than the exact total: too thin a base and the drive ruts and sinks under tyres; too thin a top and the coarse base stone pokes through the surface within months.
- Base layer: 4–6 in of coarse crushed stone. This is the strength of the driveway. Angular crushed stone locks together under weight, spreads the load of tyres and stops the surface sinking into the soil. Use the thicker end of the range on soft or clay ground.
- Top layer: 2–3 in of finer gravel. This is the finish you see and drive on. Smaller stone gives a smoother, neater surface and is easier to rake back into place when it spreads. It is also the layer that wears and migrates, so expect to top it up over the years.
A brand-new driveway therefore totals 6–8 in of stone across the two layers. Refreshing an existing driveway is much simpler: if the base is still sound, you only need a 2 in top-up of the top layer — the calculation most homeowners actually need.
Worked example: a 12 × 50 ft driveway
Take a typical single driveway, 12 ft wide and 50 ft long, built new with a 5 in base and a 2.5 in top layer — the middle of both ranges. Both layers use the same formula: area × depth in feet gives cubic feet, divide by 27 for cubic yards, then multiply by about 1.4 to get tons. The sums go like this:
- Area: 12 × 50 = 600 sq ft.
- Base at 5 in: 600 sq ft × (5 ÷ 12) ft = 250 cu ft. Divide by 27 for cubic yards: 9.26 yd³. At gravel’s usual density of about 1.4 tons per cubic yard, that is roughly 13 tons.
- Top at 2.5 in: 600 sq ft × (2.5 ÷ 12) ft = 125 cu ft = 4.63 yd³, which comes to roughly 6.5 tons.
- Total: 13 + 6.5 = about 19.5 tons of gravel across both layers.
Order 20 tons to cover compaction and spillage — stone settles as it is driven over, and a load that comes up half a ton short costs far more in a second delivery than the extra stone does. If you want to check the cubic-yard step on its own, the Cubic Yard Calculator does that single conversion.
How much gravel for common driveway sizes
The worked example works out to about 0.0325 tons of gravel per square foot of driveway, both layers included. Multiply any driveway’s area by that rate and you have a solid estimate. Here are the totals for the sizes that come up most often, at the same depths as the example — a 5 in base plus a 2.5 in top:
| Driveway size | Total gravel (both layers) |
|---|---|
| 12 × 20 ft | About 7.8 tons |
| 12 × 30 ft | About 11.7 tons |
| 12 × 50 ft | About 19.5 tons |
| 16 × 40 ft | About 20.8 tons |
| 20 × 50 ft | About 32.5 tons |
For any other size — an L-shaped drive, a parking area, a long rural track — run the two layers through the Gravel Calculator separately and add the results. The calculator also lets you change the depth, so you can price a thicker base for soft ground in seconds.
Before you order
- Measure the driveway properly: length × width in feet, section by section if it widens or narrows. Guessing the area is where most orders go wrong.
- Dig a small test hole at the edge to check what is already there. If the existing base is sound, you may only need the top layer at all.
- Order the two layers as separate loads where you can. Base stone goes down first and is compacted, then the top layer — mixing them undoes the point of having layers.
- On soft or wet ground, budget for a thicker base or a geotextile membrane under it. Both are far cheaper than re-doing a sunken drive.
- Ask for delivery in bulk once you pass a few tons. Bagged gravel costs several times more per ton and leaves you with a pile of packaging.
Finally, run your own measurements through the Gravel Calculator before you phone the supplier. Arriving with your cubic yards and tons already worked out makes the conversation quicker and the quotes easier to compare.
Frequently asked questions
How much gravel do I need for a 12×50 driveway?
About 19.5 tons in total, split across the two layers: roughly 13 tons of coarse base stone at 5 in deep and 6.5 tons of finer top gravel at 2.5 in deep. Order 20 tons to cover compaction and spillage.
How deep should a gravel driveway be?
A new gravel driveway should total 6–8 in of stone: a 4–6 in coarse base layer for strength, topped with 2–3 in of finer gravel as the driving surface.
Can I just add gravel on top of an old driveway?
Yes — that is the usual way to refresh one. If the base is still firm and level, a 2 in top-up of the top layer restores the surface without rebuilding the whole drive.
How often does a gravel driveway need topping up?
Expect to add a thin layer every 1–3 years, depending on use. Steep drives and drives used by heavy vehicles lose and move their top stone faster than flat, lightly used ones.
Estimates only — soft ground may need a thicker base or a membrane; when in doubt, ask your stone supplier.