Gravel Calculator

Gravel Calculator: How Much Gravel Do I Need?

Gravel looks simple until you have to order it: it is sold by the ton and the cubic yard, but the space it has to fill is measured in feet and inches. If you are asking how much gravel do I need, the answer rests on three things — the area, the compacted depth, and the density of the stone. This page does that maths for you in imperial or metric units, shows every formula it uses, and helps you compare bags with a bulk load before you spend anything.

Quick answer

At 1.4 tons per cubic yard, a 10 × 20 ft driveway at 4 inches deep needs 2.47 cubic yards, about 3.5 tons, before any extra allowance. The table below uses the same density and no extra, so you can check every row against the formulas further down. Most people then add about 10% for settling, uneven ground and spillage — the calculator below adds that allowance for you.

Area	Depth	Cubic yards	Weight at 1.4 tons per yd³
100 sq ft	3 inches	0.93 yd³	about 1.3 tons
200 sq ft (a 10 × 20 ft driveway)	4 inches	2.47 yd³	about 3.5 tons
300 sq ft	4 inches	3.70 yd³	about 5.2 tons
500 sq ft	4 inches	6.17 yd³	about 8.6 tons

Check: one cubic yard covers about 81 sq ft at 4 inches deep, so 200 sq ft ÷ 81 is about 2.47 cubic yards.

The formulas

Everything on this page rests on one idea: gravel fills a volume, so volume = area × depth. For a rectangle the area is length × width. For a circle the area is π × radius², where the radius is half the diameter. The depth has to be in the same unit as the sides, so square feet × (depth in inches ÷ 12) gives cubic feet. An odd-shaped area is not a problem: split it into rectangles and circles, work out each piece and add the areas together.

From there the conversions are fixed. Cubic yards = cubic feet ÷ 27, because one cubic yard is 3 ft × 3 ft × 3 ft. Cubic metres = cubic feet × 0.0283 — in metric mode the same maths runs directly in metres, so area in m² × depth in metres gives m³. Weight = cubic yards (with extra) × density, and bags = cubic feet (with extra) ÷ bag size, always rounded up, because you cannot buy part of a bag. The extra allowance is applied last, on top of the exact volume.

Weight is the one figure that can only ever be an estimate. Volume is plain geometry, exact for the measurements you give. Weight depends on density, and density changes with the stone itself — dense granite weighs more than lighter limestone — with particle size and how tightly the pieces pack, and with moisture: wet gravel weighs more than dry gravel while filling the same space. That is why density defaults to 1.4 tons per cubic yard, can be changed across the usual 1.3–1.6 range, and why a supplier’s weighbridge ticket is the figure you pay on.

Worked example

Take a driveway that measures 10 ft by 20 ft, to be covered 4 inches deep, at the default density of 1.4 tons per cubic yard:

• Step 1 — area: 10 ft × 20 ft = 200 sq ft.
• Step 2 — volume in cubic feet: 200 sq ft × 4 in = 200 × (4 ÷ 12) = 66.7 cu ft.
• Step 3 — cubic yards: 66.7 ÷ 27 = 2.47 yd³.
• Step 4 — weight: 2.47 × 1.4 = 3.46 tons, about 3.5 tons.
• Step 5 — with the default 10% extra: 2.47 × 1.10 = 2.72 yd³, and 3.46 × 1.10 = 3.80 tons — so order about 2.7 yd³ / 3.8 tons.

Those are exactly the numbers the calculator gives for the same inputs, so you can check any result on this page by hand in a minute or two.

How deep should gravel be?

The right depth depends on what the gravel has to do. As a guide, by project:

• New driveway — 4–6 inches in total, laid in layers: a coarse base layer spread and compacted first, then a finer top layer. A single thin layer tipped straight onto soil will mix into the ground, rut and vanish.
• Driveway top-up — 2–3 inches over existing gravel that is still sound and compacted. You are restoring the surface, not rebuilding the base.
• Paths and patios — 2–3 inches over a compacted base. Deeper loose gravel on a path feels unstable underfoot and migrates onto lawns and floors.
• French drains — fill the trench: the trench is filled with gravel around the pipe, so allow for the whole trench volume. A typical trench 12 inches wide × 18 inches deep holds about 1.5 cu ft of gravel per linear foot, less the space the pipe itself takes up.
• Shed bases — 3–4 inches of gravel or crushed stone, levelled and compacted, gives a firm, free-draining platform that keeps timber off wet ground.

One point matters in every case: these depths are the compacted depth. Loose gravel settles under its own weight, traffic and rain, so spread it a little thicker than the finished depth you want, or keep the 10% extra allowance and top up low spots once the layer has settled.

Types of gravel

• Crushed stone — angular pieces that lock together when compacted. This is the working material for driveways and bases, because the edges grip instead of rolling.
• Pea gravel — small, rounded stones. Easy to spread and kind underfoot, so it suits paths, play areas and drainage. The same rounded shape shifts under tyres, which makes it a poor driveway surface.
• River rock — larger rounded stones, chosen for looks. Decorative in beds, borders and around water, but it does not compact into a firm, walkable surface.
• Crusher run / MOT Type 1 — a graded base material that includes smaller particles and fines, so it compacts hard and flat. MOT Type 1 is the UK term for this kind of graded sub-base material; use it under a driveway or base, not as a decorative finish.

Ordering language changes by country. In the US, gravel is ordered in tons and cubic yards, and small bags are commonly 0.5 cu ft. In the UK, orders are in tonnes, loose or in bulk bags of about 850 kg; in Australia, in tonnes and cubic metres. The calculator’s metric mode uses tonnes and m³ and counts 20 kg bags by weight.

Bags vs bulk

Bags suit small patches — under about half a ton, say a worn spot by a gate or a small repair. They are clean to carry in a car, easy to store, and there is no minimum order and no heap to deal with. Beyond that sort of quantity, bulk by the truckload is far cheaper per ton, because you are not paying for bagging, plastic and handling on every bag, and one delivery can cover a whole driveway in a single trip.

Before ordering bulk, think about delivery as carefully as quantity. There may be a delivery charge or a minimum load, and the truck needs somewhere it can tip: check access width, low branches and cables, and soft ground it could sink into. Tip as close to the project as you safely can — gravel is heavy, and every extra barrow run is work you have given yourself. If a truck cannot reach, bags or bulk bags placed where you need them may be the practical answer.

Gravel guides

Prefer to work it out on paper first, or want the reasoning behind the numbers? These two guides walk through the maths step by step:

• Pea Gravel Calculator: How Much Do You Need? — Depths, tons and bags for pea gravel paths, patios and play areas.
• Gravel Driveway Calculator: How Much Gravel for a Driveway? — Two-layer driveway maths — base and top — with tons for common driveway sizes.

Frequently asked questions