Gravel Calculator

What this sheet does that the ranking gravel calculators do not

Not one of the seven pages that rank for gravel calculator cites a source for the density it converts yards into tons with, the only number in the calculation that is not arithmetic. Everything below was missing from all seven:

• A density with its source printed next to it. Type your supplier’s number in and theirs wins, on the takeoff too.
• Materials we could not source have no default at all, not a number we made up.
• Compacted to loose, with a labelled federal ratio instead of an arbitrary “add 10 percent.”
• Up to four areas of three shapes, added together, priced two ways and costed against a truck capacity you control.
• Short tons and metric tonnes side by side, about 10 percent apart.
• A dimensioned plan and section, plus a takeoff you can export as CSV or print.

How to calculate gravel, stone or rock

1. Get the area in square feet. Length times width for a rectangle, pi times the diameter squared divided by four for a circle, base times height divided by two for a triangle.
2. Convert the depth to feet. Inches divided by 12: 4 inches is 0.3333 ft.
3. Multiply and divide by 27. Area times depth is cubic feet; 27 cubic feet make a cubic yard.
4. Convert to tons with a density you can defend. Cubic yards times pounds per cubic yard, divided by 2,000.

Area           A  =  L x W        rectangle
                  =  pi x D^2 / 4  circle
                  =  B x H / 2     triangle
In-place vol   Vp =  sum( A x Depth )        (feet)
Loose volume   Vl =  Vp x R                  (R = compacted-to-loose ratio)
Cubic yards    Y  =  Vl / 27
Order          Yo =  ceil( Y / 0.5 ) x 0.5
Weight         W  =  Y x density(lb per cu yd)
Short tons     T  =  W / 2000
Metric tonnes  t  =  W / 2204.62
Loads          N  =  ceil( Yo / truck capacity )

One cubic yard covers 81 square feet at 4 inches, pure geometry whatever the material is. But one short ton of dry 1/4-2 in gravel is about 0.7 cubic yards, and that moves by a third if the material or weather changes.

Density: the number every other calculator hides

Aggregate weight changes with the rock it was crushed from, the gradation, and how wet or compacted it is. The table below is what Caterpillar publishes in its earthwork volumes reference tables: loose weight, and the bank weight of the same material undisturbed in the ground. The last column is not Caterpillar’s, it is the FHWA Exhibit 5.1 A ratio applied to a compacted depth, blank wherever that table has no row.

The last three rows are yard charts from Marenakos Rock Center and North Bay Materials, describing material as delivered, damp. Pea gravel, road base, decomposed granite, asphalt millings and riprap have no density at all: we could not open a document that publishes one, so the sheet asks for yours instead.

Compacted or loose: the conversion that changes the order

A base course is specified compacted, and sold loose off a conveyor: order the compacted number and you will be short. With the toggle on, the sheet multiplies your volume by one published ratio: embankment weight over loose weight of the same material. For gravel that is 1.31 — 3,570 over 2,730 lb per cubic yard, the FHWA dry row, average gradation — so the order is 31 percent larger than the layer. It is a volume ratio from the dry rows, whatever moisture state you weigh at. A figure typed in the compaction allowance field wins and prints as yours. Switch the toggle off when you measured a loose pile or a truck box already.

Read this before trusting the number. The ratio comes from Exhibit 5.1 A of the FHWA Federal Lands Highway Project Development and Design Manual: dry gravel weighs 2,700 to 2,770 lb per loose cubic yard and 3,150 to 4,130 lb per cubic yard of finished embankment, and dividing the second by the first gives the loose yards one compacted yard takes. The manual says those values “may be used for estimating purposes prior to obtaining the project specific information from the Geotechnical Unit” and footnotes the factors as subject to ±33 % variation. Read embankment as a highway fill compacted to specification, not a plate-compacted 4 in base: your supplier, spec or soils report governs.

Crushed stone is the exception, and it is deliberate. Caterpillar's 4,500 lb/yd3 bank figure describes solid rock in the quarry face before it is blasted, not a compacted base course, and the FHWA table's compacted rows are soils, not rock: neither is used for ordering here. Put your quarry’s bulking figure in the compaction allowance field if the spec is a compacted depth. The section drawing shows the compacted depth solid and the loose depth dashed above it.

Tons, tonnes and cubic yards

A short ton is 2,000 pounds, the US unit your local quarry means when it says “ton”. A metric tonne is 1,000 kilograms, which is 2,205 pounds: about 10 percent heavier. A cubic yard is not a weight, it is 27 cubic feet of space. This sheet prints all three so a quote in one unit can be checked against another.

Those are loose, finished depths. Compacted, apply the ratio: 100 sq ft of compacted 4 inch base needs 1.62 cu yd loose, not 1.23.

Worked example: a 100 ft driveway at 4 inches

1. Area: 100 ft x 10 ft = 1,000 sq ft.
2. Depth: 4 in / 12 = 0.3333 ft, the compacted layer.
3. In-place volume: 1,000 x 0.3333 / 27 = 12.35 cu yd.
4. Loose volume: 12.35 x 1.31 = 16.17 cu yd.
5. Order, rounded up to the half yard: 16.5 cu yd.
6. Weight at 2,850 lb/cu yd: 23.51 short tons.
7. Loads at 10 cu yd: 2.
8. At $42/ton: $987.53; at $58/cu yd: $957.

Add a 14 ft fire-pit circle at 3 inches — 154 sq ft, 1.87 more loose cubic yards — and it joins the same order.

Price per ton, truck loads and the takeoff

Quarries sell by the ton; landscape yards sell by the yard. Enter both and the sheet prices the order twice and names the cheaper one: on the driveway example, $42 per ton and $58 per cubic yard are only $30.53 apart on a 16.5 yard load. Delivery is usually a flat charge per load; a nearby yard can beat a cheaper quarry on the haul alone.

Loads are counted against a capacity you set, 10 cubic yards by default — ask what the truck is rated to carry legally, not what the box holds. Export CSV writes every line with a header carrying the sheet number, unit system and page URL; Print gives a one-page estimate with the drawings attached.

Frequently asked

How do I calculate how much rock I will need?

Multiply the area by the depth, both in feet, and divide by 27. A 100 by 10 ft driveway at 4 inches is 1,000 sq ft x 0.3333 ft = 12.35 cu yd in place. If that is the compacted layer, multiply by the 1.31 FHWA ratio: 16.17 cu yd loose, 16.5 rounded up to the half yard, about 23.51 short tons.

How many cubic yards is 1 ton of gravel?

0.7 cubic yards for dry 1/4-2 in gravel, 0.59 for the same gravel wet, and 0.74 for crushed stone. There is no single conversion: it is 2,000 divided by the pounds per cubic yard of the material in front of you, which is exactly why this sheet shows the density it used and lets you replace it.

Is 3 cubic yards 3 tons?

No. Three cubic yards of dry gravel weighs 3 x 2,850 = 8,550 lb, which is 4.28 short tons. Yards and tons only match for a material weighing 2,000 lb per cubic yard, and almost no aggregate does: mulch is lighter, every gravel is heavier.

Limits of this sheet

C-101 calculates volume, weight, loads and material cost for a layer of aggregate. It does not design a base course, check bearing capacity, or size a gradation. Every density is a published figure for a material like yours, not a measurement of the pile you are buying; the truck capacity (10 cu yd) and the 0.5 cu yd rounding are this sheet’s assumptions, both editable. Crushed stone and the supplier blends have no row in the FHWA table, and its topsoil and loam rows describe a highway embankment, not a garden bed: for all of them a compacted depth is ordered as measured until you type an allowance. Quantities are for planning and ordering, not engineering.