Driveway Gravel Calculator: Yards, Tons, Cost

Quick answer: the driveway gravel formula

A driveway gravel calculator does three things in sequence. It turns your area and depth into a volume, converts that volume into weight using the material's density, then divides by bag size if you are buying in bags. A driveway usually needs that calculation run twice, once for the sub-base and once for the surface layer.

The divisor of 324 comes from combining two conversions: depth in inches is divided by 12 to get feet, and cubic feet are divided by 27 to get cubic yards. 12 × 27 = 324, so the whole calculation collapses into a single step.

For driveway material, GravelScope uses a planning density of 2,700 lb per cubic yard. That is the figure behind the calculator's general, crushed stone and river rock presets, and it matches the crushed stone row in the site's density reference, so the worked examples below and the live tool will give you the same answers. It is a planning assumption rather than a product specification: actual bulk density varies with the source rock, the grading and the moisture content, so a supplier's published density should take precedence. Substituting that figure into the calculator's custom density field is the single most useful refinement for a large order.

Two reciprocal figures follow from that density, and getting comfortable with them makes almost every driveway question easier. One cubic yard weighs about 1.35 short tons. And one short ton occupies about 0.74 cubic yards, because 2,000 ÷ 2,700 = 0.74.

This page answers the quantity question only: how much material. For how deep each layer should be, see the gravel depth guide; for which stone to specify, see types of gravel; for what the job will cost, see the gravel cost guide.

Why a driveway is not a path

A driveway has to carry vehicle loads, shed water and resist the material being pushed aside by tyres. That changes the material and the build-up, not just the area.

Most driveways are built as two distinct layers. A sub-base of larger angular crushed stone, commonly MOT Type 1 in the UK, spreads the load and forms a firm platform. A surface layer of smaller stone, often 14–20 mm angular crushed gravel, sits on top and provides the finished, walkable and drivable surface. The two layers use different materials, different depths and often different densities, so they should be calculated separately and then added together.

This is the single biggest difference from a garden path, where one layer of decorative stone is usually enough. Treating a driveway as one thick layer of one material usually over-orders the expensive surface stone and under-orders the cheap sub-base, which is the worst of both outcomes.

Rounded stone such as pea gravel is a poor driveway surface. Smooth, single-size particles roll over one another rather than interlocking, so they migrate under tyre loads and will not hold a firm edge. Angular crushed stone is the usual choice, because the irregular faces lock together when compacted.

Every figure here is a bulk density: the weight of the stones plus the air between them, in the loose state in which material leaves the truck or the bag. It is not particle density, which describes the solid rock alone and is far higher. Bulk density is the correct basis for ordering material, and particle density should never be used for it.

Step-by-step: how to calculate driveway gravel

An error early in the sequence is multiplied by everything that follows. Depth is the usual culprit: a half-inch mistake on a long driveway changes the volume meaningfully, and an under-specified sub-base will not compact to a firm platform no matter how much surface stone goes on top.

Driveway gravel by depth

The table below shows the quantity needed per 100 square feet of driveway at each common layer depth, using the 2,700 lb/yd³ planning density. Use it to sanity-check each layer's figure before you add them together.

Notice how quickly depth multiplies. Going from a 2 in surface to a 4 in sub-base roughly doubles the material, and a 6 in sub-base triples the 2 in figure. That is why specifying a thicker base than the job needs is expensive, and why specifying a thinner one than the job needs is a false economy.

Two-layer driveways: sub-base plus surface

For a typical car driveway, the material is bought in two lots:

Calculate each layer over the same area, at its own depth, and then add the two results. Do not average them into one thick single layer, because the two layers use different products and are usually priced and delivered separately.

Compaction is the reason the sub-base figure needs care. Loose stone reduces in volume when it is compacted, so some guides quote a reduced compacted depth against a larger loose order depth. GravelScope's figures are loose, as-delivered quantities, which is the right basis for buying: you pay for the material as delivered, not for how much it settles afterwards. If your supplier quotes a compacted depth, ask them to convert it to an order volume before you compare against these numbers.

Coverage: how much area does a ton of driveway gravel cover?

This is the question that reverses the calculation. Instead of asking what a given area needs, ask how far a fixed quantity will spread.

At 2,700 lb per cubic yard, one short ton of driveway gravel is 2,000 ÷ 2,700 = 0.74 cubic yards, which is about 20 cubic feet. Divide that volume by the depth to get an area.

The relationship is linear, which makes it easy to reason about: doubling the depth halves the area. At 2 inches — a typical surface-layer depth — a single ton covers about 120 square feet, a strip roughly 10 feet wide and 12 feet long. That is why a modest driveway consumes several tons in the surface layer alone, before the sub-base is counted at all.

If you are working in metric, the same ton covers about 11.1 square metres at 2 inches. Note carefully that a US short ton is 2,000 lb while a metric tonne is 1,000 kg, or about 2,205 lb. A tonne is about 10% heavier, so it covers proportionally more area. Mixing the two units is a common and expensive error.

Worked examples

Three realistic scenarios, each calculated with the driveway density of 2,700 lb per cubic yard.

Example 1 — A single-car driveway, 10 ft × 20 ft, one 4 in layer

Area = 10 × 20 = 200 sq ft. Volume = 200 × 4 ÷ 324 = 2.47 cubic yards. Weight = 2.47 × 2,700 ÷ 2,000 = 3.33 short tons, which is about 6,667 lb. In 50 lb bags that is 6,667 ÷ 50 = 133.3, rounded up to 134 bags — a clear sign this project should be bought in bulk.

Example 2 — A double driveway, 20 ft × 20 ft, with a sub-base and a surface

Area = 20 × 20 = 400 sq ft. Sub-base volume = 400 × 4 ÷ 324 = 4.94 cubic yards. Surface volume = 400 × 2 ÷ 324 = 2.47 cubic yards. Total = 7.41 cubic yards. Sub-base weight = 4.94 × 2,700 ÷ 2,000 = 6.67 short tons. Surface weight = 2.47 × 2,700 ÷ 2,000 = 3.33 short tons, for a total of 10.00 short tons.

The two layers here are different products bought separately, so keep the orders distinct: about 4.94 yd³ of Type 1 sub-base and about 2.47 yd³ of 20 mm surface gravel. Adding a 10% allowance to each would take the order to roughly 5.43 yd³ and 2.72 yd³.

Example 3 — A rural driveway, 12 ft × 100 ft, with a 10% allowance

Area = 12 × 100 = 1,200 sq ft. Sub-base at 4 in = 1,200 × 4 ÷ 324 = 14.81 cubic yards. Surface at 2 in = 1,200 × 2 ÷ 324 = 7.41 cubic yards. With a 10% allowance: 16.30 yd³ of sub-base and 8.15 yd³ of surface. Sub-base weight = 16.30 × 2,700 ÷ 2,000 = 22.00 short tons. Surface weight = 8.15 × 2,700 ÷ 2,000 = 11.00 short tons.

At this size the job is firmly a delivery-scale job: roughly 33 short tons of material in total, which is several truckloads. On a long rural driveway the 10% allowance is well justified, because edges settle and a long run is hard to top up evenly later.

All three examples can be reproduced in the GravelScope gravel calculator by selecting the material preset, entering the dimensions and depth, and setting the allowance to 0 or 10%. The calculator applies the same density and the same rounding, so the outputs should agree.

Bag size and bag counts

Bagged gravel is sold by weight, and the bag weight is different from the bag volume. A 50 lb bag of crushed gravel at 2,700 lb/yd³ holds about 0.50 cubic feet. A 40 lb bag holds about 0.40 cubic feet.

Always round the bag count up. If the arithmetic gives 133.3 bags you need 134, because a supplier cannot sell you a third of a bag. The rounding is slight, but it is easy to arrive one or two bags short and have to make a second trip.

For a driveway, bags are usually the wrong unit entirely: even the smallest example above needs 134 of them. Use bag counts to understand the scale of the job and to fill small gaps at the edges, and buy the bulk of the material loose by the ton or the cubic yard.

Estimating driveway gravel cost

Cost is deliberately kept out of the quantity calculation, because the price of a driveway is driven by factors a volume calculation cannot see: the material, the haul distance, whether the truck can reach the site, and how much preparation the ground needs.

The material cost follows directly from the tonnage you just calculated, but the other three lines can rival or exceed it. The gravel cost guide works through each component, and the calculator's optional price field will multiply your tonnage by a price per ton if you want a first-pass material figure.

Choosing a driveway gravel type

Quantity and material choice are separate decisions, and this page deliberately keeps them separate. The table below is a summary only; the full comparison of sub-base grades, sizes and what each is used for lives in the types of gravel guide.

Two points matter here. Angular material is the correct family for a driveway: rounded gravel will not interlock or hold an edge under tyres. And the sub-base and the surface are normally different products, so specify each layer separately rather than ordering one material for the whole build-up.

Ordering and allowances

Once you have a layer-by-layer tonnage, the last decision is how much extra to order. An allowance is not an automatic percentage; it is a response to specific risks in your site.

Reasons a driveway order might justify an allowance include uneven or soft ground that will take extra material to level, edges that will settle and need topping up, a long delivery distance where a second trip is expensive, and a surface that will be refreshed in future. Reasons it might not include a flat, firm, well-measured site with a supplier who will deliver a short second load cheaply.

The extra gravel allowance guide works through the trade-off in detail, and the calculator's allowance field applies the percentage for you. For a driveway, a 10% allowance on each layer is a common planning starting point, applied per layer rather than to the combined total, so that a shortfall in the cheap sub-base does not silently reduce the order of the expensive surface.

Mistakes that change the answer

• Calculating one layer when the job needs two. A driveway that carries cars normally needs a sub-base plus a surface, calculated separately. Collapsing them into one depth of one material mis-budgets both.
• Confusing a compacted depth with a loose order depth. These figures are loose, as-delivered quantities. A depth quoted as compacted needs converting back to an order volume before you compare.
• Using rounded gravel as a driveway surface. Pea gravel and river rock migrate under tyres and will not hold an edge, however much you order.
• Mixing short tons and metric tonnes. A tonne is about 10% heavier than a short ton, which is a real error on a multi-tonne driveway order.
• Forgetting the area is the driven surface, not the plot. Measure the finished driveway footprint, including any turning area, not the whole frontage.
• Treating a rounded grade figure as exact. Density varies by product; a supplier's stated density always beats a general planning figure.

Use the GravelScope driveway gravel calculator

The GravelScope gravel calculator supports both unit systems, three shape modes, material presets, a custom density field, a waste allowance, bag counts and an optional price per ton. To size a driveway, calculate the sub-base and the surface as two separate passes and add the results.

Enter the driveway length and width, choose the material preset that matches the layer, set the depth for that layer, and read the cubic yards, tons and bag count. Then repeat for the second layer with its own material and depth. The result note records the density used, so you can substitute a supplier's figure when you have one.

Sources and further reading

The density and conversion logic in this guide is explained rather than invented, and the figures can be checked against the references below. Where a source states a range, the range is reported as published.

• Mass, Weight, Density or Specific Gravity of Bulk Materials — bulk density reference for over 300 dry materials, whose "Stone, crushed" entry (100 lb/ft³) is the origin of the 2,700 lb/yd³ planning figure used here. It is cited as a general reference for loose bulk aggregate density, not as a product specification.
• Gravel — background on how gravel is defined and graded, including the distinction between natural gravel and manufactured crushed stone, and a widely cited order-of-magnitude figure of roughly 1,800 kg per cubic metre for loose gravel.
• NIST Office of Weights and Measures — Unit Conversion — the authoritative approach to unit conversion and rounding, and the source for using exact conversion factors rather than approximations.
• USGS National Minerals Information Center — Crushed Stone Statistics and Information — government statistics on crushed stone and construction sand and gravel supply in the United States, and context for how aggregate is classified and used.

Two limitations are worth stating plainly. First, no single density figure is correct for every driveway product, because the stone's origin and grading vary; the 2,700 lb/yd³ used here is a planning figure, and a supplier's stated density always overrides it. Second, these calculations describe material quantity, not structural design. Load-bearing capacity, drainage, sub-base specification and edge restraint decisions need an assessment that a volume calculation cannot provide.

Driveway gravel calculator FAQ