Why gravel is ordered in tons but measured in cubic yards
A quarry weighs your load on a scale and bills you by the ton. You, standing in a driveway with a tape measure, are working in feet and inches. Everything about a gravel order hinges on the bridge between those two worlds, and that bridge is bulk density — the weight of one loose cubic yard of the material as it comes off the conveyor.
The chain is short. Measure the plan area in square feet. Multiply by the depth in feet to get cubic feet. Divide by 27 to get cubic yards, because a cubic yard is 3 ft × 3 ft × 3 ft. Multiply by the material's density in pounds per cubic yard, then divide by 2,000 to get US short tons. Every step is exact except one: the density, which depends on the rock, its gradation, and how wet it is that morning.
That single uncertainty is why two suppliers can quote the same driveway and disagree: one working from 2,700 lb/yd³ and one from 2,900 lb/yd³ will differ by 2,900 ÷ 2,700 = 7% on the invoice, and both are right. Washed #57 stone — the rounded, open-graded material used for drainage beds and pipe bedding — carries a lot of void space and weighs less per yard than crusher run, which contains fines that pack into the gaps. Sand weighs differently wet than dry. If the number matters, ask the quarry for the density on the ticket rather than trusting a chart.
The formula, term by term
Start with area. For a rectangle it is length times width. For a circular pad it is π times the radius squared, which is why the calculator asks for a diameter and halves it for you — entering a radius where a diameter belongs quadruples the answer, and it is the single most common data-entry error on any round-area takeoff.
Next, depth. It is entered in inches because that is how depths are specified on plans and in conversation, but volume needs consistent units, so D is divided by 12. A 4 in layer is 0.3333 ft. Multiply area by that and you have cubic feet.
Then the two constants. 27 converts cubic feet to cubic yards. 2,000 converts pounds to US short tons — not 2,204.6, which is a metric tonne, and not 2,240, which is a long ton still used in some marine and steel contexts. Ordering in the wrong ton costs you about 10%.
Finally the compaction allowance c. Gravel arrives loose and ends up rolled. A layer placed at 4 in loose and compacted to 3½ in has lost volume you paid for, so ordering slightly more than the geometric volume is normal practice. The allowance is not a physical constant — it is a purchasing decision, and 10% is a common working figure for a driveway that will be plate-compacted or rolled. Set it to zero when you are filling a fixed void such as a trench or a form, where the geometry is the geometry.
Worked example: a 40 ft × 12 ft driveway at 4 in of #57 stone
You are topping a residential drive 40 ft long and 12 ft wide with 4 in of washed #57 crushed stone at 2,700 lb/yd³, ordering 10% extra for compaction, at a delivered price of $40 per ton on a 20-ton tri-axle.
- Area. 40 ft × 12 ft = 480 ft².
- Depth in feet. 4 in ÷ 12 = 0.33333 ft.
- Volume in place. 480 × 0.33333 = 160.0 ft³.
- Add the allowance. 160.0 × 1.10 = 176.0 ft³.
- Cubic yards. 176.0 ÷ 27 = 6.519 yd³.
- Weight. 6.519 × 2,700 = 17,600 lb.
- Tons. 17,600 ÷ 2,000 = 8.80 tons.
- Truckloads. 8.80 ÷ 20 = 0.44, so one load, part-filled.
- Cost. 8.80 × $40 = $352.00.
Check it a second way. A cubic yard of 2,700 lb/yd³ stone weighs 1.35 tons, and one cubic yard spread 4 in deep covers 27 ÷ 0.33333 = 81 ft². So 480 ft² needs 480 ÷ 81 = 5.926 yd³ before allowance, 6.519 yd³ after — the same figure, reached from the other direction. Getting the same answer twice by different routes is the cheapest insurance there is on a takeoff.
How to read the result and how deep to actually go
The tonnage is only as good as the depth you fed it, so spend your attention there. For a new gravel driveway on a prepared subgrade, the usual build is a 4 in compacted layer of dense-graded base such as crusher run, followed by a 2–3 in wearing course of angular stone. Topping up an existing drive that has held its shape typically takes 2 in. A walkway or decorative bed is generally 2–3 in of stone over fabric. Pipe bedding and drainage trenches are set by the pipe manufacturer or the plan detail, commonly 4–6 in under the pipe.
Look hard at the truckload count. Freight is a large share of a small gravel order, and the marginal cost of the last few tons is often near zero if the truck is coming anyway. If the calculator says 2.1 loads, either trim the depth slightly or accept three-quarters of a wasted trip — but decide deliberately, because a 5% short order means a second delivery charge for a couple of tons.
Finally, sanity-check the weight against the truck. As a working rule a tri-axle dump hauls around 20 tons and a tandem around 12, though the legal payload depends on your state's axle-weight limits; if your answer is 45 tons you are buying three trucks, and the driveway you are dumping on needs to survive them. For a materially different check on the same site, the trench excavation volume calculator handles bedding stone inside a trench, and the concrete slab calculator covers the slab that may sit on top of this base.
Coverage per cubic yard and per ton at common depths
| Depth | ft² per yd³ | ft² per ton | yd³ per 100 ft² | Tons per 100 ft² |
|---|---|---|---|---|
| 1 in | 324 | 240 | 0.309 | 0.417 |
| 2 in | 162 | 120 | 0.617 | 0.833 |
| 3 in | 108 | 80 | 0.926 | 1.250 |
| 4 in | 81 | 60 | 1.235 | 1.667 |
| 6 in | 54 | 40 | 1.852 | 2.500 |
| 8 in | 40.5 | 30 | 2.469 | 3.333 |
| 12 in | 27 | 20 | 3.704 | 5.000 |
Tons columns assume 2,700 lb/yd³ (1.35 ton/yd³). For crusher run at 2,800 lb/yd³ multiply the ton figures by 2,800/2,700 = 1.037; no compaction allowance is included.
Which material, and what the size numbers mean
The number on a stone product — #57, #8, #4 — is a gradation designation from ASTM D448 (and the identical AASHTO M 43 table), which specifies the percentage of each product that must pass a given sieve. It is not a diameter. #57 is the workhorse: nominally 1 in down to about ¼ in, with the fines washed out, so it drains freely and does not compact into a solid mass. That makes it right for drainage beds, pipe bedding, and the top course of a drive, and wrong as a structural base on its own.
Crusher run (also sold as ABC, dense-graded aggregate, Class 5 or ¾-minus depending on region) is not an ASTM D448 product at all — it is the crusher's whole output including the dust. The fines fill the voids between the stones, so it compacts to a hard, load-bearing layer, and it weighs more per cubic yard because there is less air in it. Use it for base under a drive, a shed pad, or pavers.
Screenings or stone dust is the fine fraction alone, used for setting beds and as a levelling course. River rock is rounded and will not lock together, so it stays loose forever; it is a landscape product, not a structural one, and it weighs less per yard because rounded particles pack poorly. If you are building a paver patio rather than a gravel surface, the paver base calculator sizes the base and bedding layers together.
Mistakes that blow a gravel order
- Entering a radius where a diameter belongs. The area is proportional to the square, so this quadruples the order.
- Mixing up tons and tonnes. A metric tonne is 2,204.6 lb and a US short ton is 2,000 lb — a 10% difference on every line of the invoice.
- Assuming one density fits everything. Washed open-graded stone and dense-graded crusher run differ by roughly 100 lb per cubic yard, and wet sand differs from dry sand by more.
- Forgetting that the depth is the compacted depth. If you specify 4 in finished and order the geometric volume with no allowance, you finish short.
- Buying the wrong product for the job. Open-graded #57 will never compact into a base, and crusher run will never drain like a French drain.
- Ignoring the subgrade. Stone placed on soft, wet clay migrates into it. Geotextile fabric between subgrade and stone is cheap compared with re-doing the drive.
- Rounding the truckload the wrong way. Ordering 0.5 tons short to save money usually buys a second delivery fee larger than the material saved.
What this calculator does not model
It assumes a flat, uniform layer over a level plan area. It does not handle a crowned or superelevated cross-section, a sloped drive where the true surface area exceeds the plan area, wedge sections where the depth varies from one end to the other, or the extra material lost into a soft subgrade. For a sloped surface, use the true along-slope length rather than the horizontal projection. For an area that varies in depth, split it into strips of constant depth and add the results.
It also assumes the density figure describes the material as delivered — loose. Densities quoted as compacted or in-place values will overstate the tonnage you need to buy.
Where this sits among the other takeoff tools
Bulk material takeoff is the same arithmetic wearing different clothes across the whole site. The volume of a trench, the volume of a paver base, the tonnage of an asphalt mat and the cubic yards in a slab all reduce to area × thickness with a unit conversion on the end; what changes is the density and the waste convention.
Use this calculator whenever the material is sold by weight and the job is described by area. Switch to the asphalt tonnage calculator when the material is hot mix, because asphalt is specified by compacted mat thickness and carries a much higher unit weight. Switch to the cut and fill earthwork calculator when you are moving native soil between stations rather than importing stone, because that problem needs swell and shrinkage factors instead of a simple density. And for garden materials sold by the yard rather than the ton, the mulch cubic yards calculator and topsoil tonnage calculator use the same geometry with lighter densities.
Density values used in this tool are nominal loose bulk densities of the kind quarries publish for ordering purposes. The laboratory procedure behind any measured figure is ASTM C29/C29M, which determines bulk density and voids in aggregate; if a specification calls for a verified unit weight, that is the test that produces it.