Road Base Calculator
Road base, gravel and bedding sand by area and finished depth — with compaction allowed for, so you order enough.
Your result
Enter your area and finished depth above to see how much to order.
This is the mistake that leaves people short. Granular material is sold loose and placed compacted. A 100 mm finished depth needs noticeably more than 100 mm of material delivered, because rolling it drives the air out.
Why compaction changes the order
Work out the finished volume the obvious way — area × compacted depth — and you get what will be there when the job is done. That is not what you buy.
Loose material contains air. Rolling it closes those voids, so the pile shrinks as it is compacted. Road base typically loses around 20–25% of its loose volume; cleaner, rounder materials like gravel and sand lose less, usually around 10%.
Loose volume = compacted volume × compaction factor
So 20 m² at 100 mm finished is 2 m³ in place, but about 2.5 m³ of road base delivered. Order 2 m³ and you finish roughly 20 mm shallow across the whole area, which on a driveway base is the difference between a surface that lasts and one that moves.
Why the result is in tonnes as well
Quarries and landscape suppliers almost always sell by weight, not volume. Road base runs about 2.1 tonnes per loose cubic metre, gravel and sand nearer 1.6. The tonnage figure is the one you will actually be quoted on, so it is shown alongside.
These figures are typical, not universal
Compaction and density both depend on the specific material, its moisture content, and how thoroughly it is rolled. A vibrating plate on a garden path does not achieve what a roller does on a driveway.
Your supplier knows their own material and can give you real figures for it. Treat the defaults here as a starting point for ordering, and ask when the quantity matters.
Typical depths
General examples, not a specification — the right depth depends on the ground underneath and what will drive on it:
- 50–75 mm — garden paths, bedding under pavers.
- 100 mm — common base under a domestic concrete slab or path.
- 100–150 mm — driveways taking cars.
- 150 mm and up — heavier vehicles, or soft and reactive ground.
Deep base on soft ground is not a substitute for dealing with the soft ground. If the subgrade moves, the base moves with it.
Frequently asked questions
Should I lay it in layers?
Yes, for anything over about 100 mm. Compacting a deep layer in one go leaves the bottom loose, because the compaction energy does not reach it. Lay and roll in layers of roughly 75–100 mm. The total quantity is unchanged — this calculator gives the whole lot.
Does this include the concrete on top?
No, base material only. For the concrete use the concrete calculator, or the driveway calculator if that is what you are building.
Do I enter the loose depth or the finished depth?
The finished, compacted depth — the one you want when the job is done. The calculator works backwards from that to the loose volume you need to order. Entering the loose depth would double-count the compaction.
My supplier quotes in tonnes. Which number do I give them?
The "approximate weight" figure. It is the tonnage of the loose volume, including your extra allowance if you set one. Confirm their density, though — it varies by quarry and by material.