Gravel Calculator

What Is Gravel?

Gravel, in the construction sense, is loose rock fragments coarser than sand: either naturally rounded stone dug from pits and river deposits, or angular fragments produced by crushing quarried rock. Which one you buy changes how the surface behaves underfoot and under tires. How it is packaged and weighed changes what you have to order, and that second half is what this page calculates.

Rounded Gravel, Crushed Stone and Size Numbers

Rounded gravel — pea gravel, river rock, pit run — has smooth faces that roll past each other. It drains freely and is comfortable to walk on, and for exactly the same reason it will not lock together under load, which is why it migrates out of driveways and off slopes. Crushed stone is fractured on every face, so the particles wedge against one another and hold a compacted surface. A crushed product with fines in the mix (often sold as crusher run, quarry process or road base) binds hardest of all; a washed product with the fines screened out drains hardest.

Sizes are not left to the yard's imagination. Coarse aggregate gradations are standardized as numbered sizes under AASHTO M43-05, the same specification published by ASTM as D448, and a Federal Highway Administration study of open-graded backfills notes that it tested "12 of the 19 AASHTO M43 gradations" because of their common use in geotechnical work. A number such as No. 57 or No. 8 therefore describes a defined band of sieve sizes rather than a merchant's adjective, which is what makes it worth quoting when you call for a price.

None of this changes the arithmetic on this page. A cubic yard of washed river rock and a cubic yard of crusher run occupy the identical cubic yard, so the volume math is the same for every product in the yard. Where the choice does show up is in the weight of that yard, and in how much of it disappears into the ground the first time a truck drives over it.

How Gravel Is Sold: Yards, Tons and Bags

Four units collide in a single purchase — the area is in feet, the depth is chosen in inches, the delivery is quoted in cubic yards or tons, and the small stuff comes in bags. That collision is where gravel orders go wrong.

• By the cubic yard. One cubic yard is 27 cubic feet, a cube three feet on a side, and 0.7645549 cubic meters in NIST's conversion tables. This is the unit a landscape supply yard expects to hear.
• By the ton. A US short ton is 2,000 pounds, listed by NIST as 907.1847 kilograms. Quarries and larger aggregate suppliers weigh loads over a scale and bill this way, which is why a volume figure alone will not settle a quarry invoice.
• By the bag, usually 0.5 cubic feet for decorative stone. It takes 54 of them to make a cubic yard, so bags stop making sense somewhere below half a yard.
• By the scoop or the bucket at some yards. Neither is a unit of measure — ask how many cubic yards the loader bucket actually holds before comparing that price with anything else.

The calculator answers in every unit an order needs at once. It leads with cubic yards because that is what a delivery is booked in, prints cubic feet and cubic meters underneath for anyone whose supplier quotes differently, and gives the weight as a span so a per-ton conversation can start from a real number.

Building the compacted structural layer under a drive rather than spreading a loose decorative course? Dense-graded base material is figured on its own terms in the Road Base Calculator.

How Do You Calculate Gravel?

Multiply the area by the depth, add an allowance for what compaction and the soil below will swallow, then divide into cubic yards. The step most easily missed is the unit change in the middle of it: the area is measured in feet and the depth is typed in inches, so one of the two has to be converted before they are multiplied together.

The Gravel Formula, Written Out

This is what the code runs, in order:

ft3 = length × width × (depth ÷ 12) × (1 + waste ÷ 100)
yd3 = ft3 ÷ 27
m3  = ft3 × 0.028316846592

tonsLo = yd3 × 1.4
tonsHi = yd3 × 1.7

metric entry converts before anything else:
  length, width × 3.280839895      meters → feet
  depth ÷ 2.54                     centimeters → inches

cost = yd3 × price                 priceUnit = per cubic yard
cost = yd3 × 1.55 × price          priceUnit = per ton

Every conversion constant in there is exact or official. A foot is 0.3048 meters by definition, so 1 ÷ 0.3048 gives the 3.280839895 used on metric entry; an inch is exactly 2.54 centimeters; and NIST's Guide to the SI lists the cubic foot as 2.831685 × 10⁻² cubic meters, which is the 0.028316846592 in the third line.

The 324 square feet quoted at the top of this page falls straight out of the same arithmetic and is worth carrying in your head. A cubic yard is 27 cubic feet; spread it one inch — a twelfth of a foot — deep and it has to stretch over 27 ÷ (1/12) = 324 square feet. Halve the depth and it covers twice as much; double the depth and it covers half.

Step by Step

• Set the units control first. Every choice on this form is a two-button segmented control rather than a dropdown, and this one arrives on Feet (depth in inches). There is no mixed mode, so an area measured in feet needs its depth typed in inches.
• Measure the area at its widest points and enter length and width. A drive running 60 ft from the road and 12 ft wide is 60 by 12 even where the entrance flares.
• Type the depth of the layer you are spreading, not the depth of the excavation. If you are digging out 8 inches and putting 6 inches of stone back, the number the calculator wants is 6.
• Choose the compaction allowance. 5% suits a firm, prepared, already-compacted base; 10% suits soft ground, fresh excavation and uneven grade. There is no zero option, so the panel never shows the bare geometric volume.
• Leave the price box at 0 unless you have a real quote, and set Price Quoted to match the way it was given to you — per cubic yard or per ton. The two are not interchangeable and the difference is large.
• Press Calculate. The three measurement boxes arrive empty, so nothing runs on load and nothing recalculates as you type; the panel updates only when the button is pressed. Reset clears it back to the empty state.

Leave any measurement blank, zero, negative or non-numeric and the panel shows the amber notice instead of a result: "Enter length, width, and depth greater than zero". Anything above zero is accepted, though. The boxes carry no minimum or maximum and the form is submitted without browser validation, so a quarter-inch depth returns 0.16 cubic yards on a 200 sq ft area and a 240-inch depth returns 155.56 cubic yards on the same area. Nothing warns you that the second one is a swimming pool.

Worked Example: A 20 × 10 ft Path at 4 Inches

Units on feet, length 20, width 10, depth 4, allowance 5%, price left at 0. Press Calculate and the panel reads:

• 2.59 cubic yards
• = 70.0 ft³ = 1.98 m³
• Weight: about 3.6–4.4 tons (1.4–1.7 t/yd³)
• Includes 5% compaction/waste allowance

Follow it through. 20 × 10 = 200 square feet; 4 inches is a third of a foot, so the geometric volume is 66.667 cubic feet; the 5% allowance lifts that to 70.0; and 70.0 ÷ 27 = 2.5926 cubic yards, displayed as 2.59. The tonnage line multiplies the unrounded 2.5926 by 1.4 and by 1.7 to reach 3.63 and 4.41, printed to one decimal. Start again from the 2.59 on screen and the low figure comes out at 3.626 instead — close enough here, not always.

Now put a quote in. With Price Quoted on per cubic yard and 45 in the price box, a fifth line appears: "Estimated cost: $117 (at $45/yd³)". Move the control to per ton and leave 45 where it is, and the same path reads "Estimated cost: $181 (at $45/ton, 1.55 t/yd³ typical)". Type 30 instead and it reads "Estimated cost: $121 (at $30/ton, 1.55 t/yd³ typical)". The volume never moved — only the unit the price was attached to.

Entering Meters and Centimeters

Choosing meters converts before it calculates: lengths are multiplied by 3.280839895 to reach feet, the depth is divided by 2.54 to reach inches, and the volume math then runs on the converted figures. The cubic-yard headline and the tonnage stay imperial, because those are the units the material is sold in wherever this calculator is likely to be used.

A 6 × 3 m path at 10 cm deep with a 5% allowance returns "2.47 cubic yards", "= 66.7 ft³ = 1.89 m³" and "Weight: about 3.5–4.2 tons (1.4–1.7 t/yd³)". A 10 × 4 m parking area at 5 cm returns "2.75 cubic yards" and "= 74.2 ft³ = 2.10 m³". A 15 × 6 m yard at 15 cm with the 10% allowance returns "19.42 cubic yards" and "= 524.4 ft³ = 14.85 m³".

Read that cubic-meter figure carefully, because it is not the hole you measured. The first path is 6 × 3 × 0.10 = 1.80 m³ of space, and the panel says 1.89 — the allowance is inside the metric number too. Same story on the others: 2.00 m³ of space displays as 2.10, and 13.50 m³ displays as 14.85 once the 10% is added. Every volume the calculator prints is an ordering quantity, never a geometric one.

Gravel Coverage Chart

Three tables, all generated by running this calculator rather than copied from a supplier's flyer. The first is the reference worth memorizing; the second finds your job without typing anything; the third shows what the depth field alone does to a delivery.

What One Cubic Yard Covers

The middle column is pure geometry — 324 ÷ depth. The third is what one ordered yard actually reaches once the 5% allowance has taken its cut, and the last two are the calculator's answer for a 100 sq ft area at that depth.

The gap between the second and third columns is the whole argument for having an allowance at all. A supplier who says one yard covers 81 square feet at 4 inches is quoting the geometry correctly and still leaving you short of a compacted surface. Switch the allowance to 10% and that ordered yard shrinks further, to 73.6 sq ft at 4 inches and 98.2 sq ft at 3.

The coverage column halves as the depth doubles, which is enough to check a coverage figure you have been handed without doing any arithmetic. If a yard tells you a single cubic yard will do a 200 sq ft patio at 3 inches, it will not — it does 108 square feet of it, and once you have added the allowance the calculator asks for 1.94 yards to finish the job.

Gravel by Area at 4 Inches

Every row is what the panel returns at 4 inches deep with the 5% allowance, and the last column is the cost line at a worked $45 per cubic yard — your own supplier's number goes in the price box.

Area is what drives the answer, not the shape it comes in. A 12 × 10 ft shed pad at 4 inches and a 40 × 1 ft trench with the depth set to 12 both return "1.56 cubic yards" and "= 42.0 ft³", because both describe 40 cubic feet of space before the allowance is applied. An area that lands between two rows is bracketed by them; one outside the 50 to 1,000 sq ft the table spans has to be scaled instead, since the quantity tracks the area exactly — a 30 sq ft bed at 4 inches returns "0.39 cubic yards", and a 2,000 sq ft drive returns "25.93 cubic yards", double the 1,000 sq ft row.

The Same 200 sq ft at Every Depth

Depth scales the order in a straight line, which is easy to say and easy to underestimate when the tape measure has not moved. One 20 × 10 ft area, six decisions, all at the 5% allowance:

Moving a 200 sq ft path from a 2-inch dressing to a 4-inch course doubles the delivery, 1.30 yards to 2.59, without a single measurement changing. Depth carries the order in direct proportion — half the depth, half the stone — so it is worth settling with the guidance in the next section before a delivery is booked.

How to Read Your Result

The panel gives one headline figure and three or four supporting lines. Each answers a different question, and they are asked by different people — the yard wants the first, the truck scale wants the third, and your budget wants the last.

• "2.59 cubic yards" — the headline and the bulk order figure, rounded to two decimals. Round it up yourself when you call; nobody delivers hundredths.
• "= 70.0 ft³ = 1.98 m³" — the same quantity in cubic feet and cubic meters, for bagged products and for suppliers who quote metric.
• "Weight: about 3.6–4.4 tons (1.4–1.7 t/yd³)" — the span your load could weigh, in US short tons of 2,000 lb.
• "Includes 5% compaction/waste allowance" — a reminder of which allowance produced everything above it.
• "Estimated cost: $117 (at $45/yd³)" — present only when the price box holds a number above 0, and built from your quote alone.

Why the Weight Is a Range

Turn the two ends of the band into a density and you can see what it is claiming. 1.4 tons per cubic yard works out at 103.7 pounds per cubic foot; 1.7 tons per cubic yard is 125.9; and the 1.55 midpoint used for per-ton pricing sits at 114.8. Where your material lands inside that band depends on the rock it was made from, how much fine material is mixed through it, and how wet the pile is when it is loaded.

Nobody has to guess at this. ASTM C29/C29M is the standard test for the bulk density — the trade still calls it unit weight — of aggregate in a loose or compacted condition, and the standard itself says the result "may be used for determining mass/volume relationships for conversions in purchase agreements". Your supplier can quote the measured figure for the exact product in their pile, which replaces the band with a single number. That is worth asking for on a large order, where the band itself is nearly four tons wide: a 1,000 sq ft drive at 4 inches reads "Weight: about 18.1–22.0 tons (1.4–1.7 t/yd³)".

Two caveats in that standard are worth carrying with you. It cautions that "the relationship between degree of compaction of aggregates in a hauling unit or stockpile and that achieved in this test method is unknown", and it determines density on a dry basis while real aggregate carries moisture. Rain adds no stone at all, but it certainly adds tons — which is why a load bought by weight off a soaked stockpile covers less ground than the same tonnage bought dry.

How Deep Should Gravel Be?

For anything a vehicle drives on, the Federal Highway Administration's unpaved-roads handbook gives a floor: "Wearing course materials should be at least 4 in. (100 mm) thick, but preferably at least 6 in. (150 mm) thick to ensure a good crown and to facilitate maintenance activities." That is guidance for a public road carrying real traffic, and it is the most defensible number available for a driveway.

• Walkways and garden paths: 2–3 inches of small angular stone over a compacted, weed-suppressed subgrade. Rounded pea gravel at this depth is comfortable but will not stay in a defined edge without an edging strip.
• Driveway top course: 4 inches at minimum, per the FHWA figure above, with 6 preferred where the surface has to be graded and re-crowned over its life.
• Driveway base under that top course: 4–6 inches of larger, dense-graded crushed stone on prepared subgrade. Run the two layers through this calculator separately, because they are usually different products at different prices.
• Drainage — french drains, foundation beds, dry wells: 6 inches or more of washed, uniformly graded stone, precisely because the fines that help a driveway bind are the fines that stop water moving.
• Shed pads and paver bases: 4 inches of compacted base, screeded flat rather than crowned.

The same handbook is worth reading on what happens after the stone is spread. It asks for compaction "with a smooth drum or a rubber-tired roller until refusal density (that is, density checks with a nuclear gauge or similar device after each roller pass reveal no further increases) is achieved rather than just aiming for a percentage of a laboratory determined density" — which is the plainest possible statement that the loose yard you buy is not the yard you end up with.

It also sets the shape: "A target crown of 5 percent (± 1%) assures that the road surface will shed rain. A crown of less than 4 percent can lead to water ponding on the road, which is dangerous for road users and will create soft spots, which will quickly turn into potholes." A drive built dead flat is a drive that will need this calculator again sooner than one built to shed water.

Choosing Between 5% and 10%

The allowance is not padding for clumsiness. Aggregate loses volume when it is rolled, and on soft or freshly disturbed ground a measurable share of the bottom of the layer works down into the subgrade and never comes back. Pick 5% over a firm, prepared, previously compacted base; pick 10% over soft ground, fresh excavation, or a grade that still has hollows in it.

On small jobs the choice barely registers. A 12 × 10 ft shed pad at 4 inches returns "1.56 cubic yards" at 5% and "1.63 cubic yards" at 10% — the same delivery either way. On a 1,000 sq ft drive at 6 inches the two settings return 19.44 and 20.37 cubic yards, and at $45 per cubic yard the cost line moves from "Estimated cost: $875 (at $45/yd³)" to "Estimated cost: $917 (at $45/yd³)".

When the two settings straddle a whole yard, take the larger. Ordering short means a second delivery, and a second delivery fee on a half-yard shortfall costs more than the extra material would have. Landscape fabric under the layer is there to keep stone from working down into soft soil, but it does nothing about the compaction half of the loss, so laying it is not a reason to drop from 10% to 5%.

Pricing by the Cubic Yard or by the Ton

One multiplication settles this, and getting it backwards moves the cost line by a factor of 1.55 in one direction or the other. The calculator converts a per-ton price at 1.55 tons per cubic yard, so a per-yard quote and a per-ton quote are the same money when the yard price is 1.55 times the ton price. At $45 a cubic yard, the matching ton price is $29.03.

Watch it on a 600 sq ft area at 4 inches, which needs 7.78 cubic yards. Enter 45 with Price Quoted set to per cubic yard and the panel reads "Estimated cost: $350 (at $45/yd³)". Set it to per ton and enter 29, and the panel reads "Estimated cost: $350 (at $29/ton, 1.55 t/yd³ typical)" — the same job, the same money. Leave the control on per ton and the number at 45, however, and it reads "Estimated cost: $543 (at $45/ton, 1.55 t/yd³ typical)".

That last figure is not a bug; it is what $45 a ton genuinely costs when a yard weighs about a ton and a half. The control has to match the way your quote was worded, and if a supplier gives you both numbers, the one to trust is the one attached to how they will actually bill you.

Two things sit outside the cost line entirely. Delivery is not in it — no haul fee, no fuel surcharge, no fuel-adjusted mileage — and neither is the minimum load many suppliers apply before they will send a truck at all. Below about a cubic yard, ask what delivery costs before assuming bulk beats a store run; that is the size where a haul fee can outweigh the material under it.

Limits: When This Calculator Does Not Apply

The arithmetic is exact. What it is exact about is a rectangle of loose stone at one uniform depth, and gravel jobs are rarely quite that tidy.

• Rectangles only — no circle, triangle or curve mode. For a round fire-pit surround, work the circle's area out first and enter it as the length with a width of 1: a 10 ft circle is 78.54 sq ft, which at 3 inches returns 0.76 cubic yards. Enter it as a 10 × 10 square instead and you get 0.97 yards, because the square holds about 27% more than the circle inside it.
• One depth and one allowance per run. A 60 × 12 ft drive built as a 6-inch base at 10% plus a 3-inch top course at 5% is 14.67 plus 7.00 cubic yards — 21.67 in total, against the 22.00 a single 9-inch run at 10% would report. Two runs is also how you price two different products.
• It models a flat slab. A drive built to the FHWA's 5% crown carries extra material along its centerline, and if that crown is formed out of the surfacing rather than shaped into the subgrade below, the extra is a triangular prism the rectangle never contained: on a 12 ft wide, 60 ft drive it comes to 108 cubic feet, or 4.00 cubic yards.
• The allowance cannot be switched off. Five percent is the floor, so the panel never reports the plain geometric volume — including the cubic-meter line, which carries the allowance along with everything else.
• The tonnage is displayed to a tenth of a ton, so small differences vanish. A 100 sq ft area at 3 inches reads "Weight: about 1.4–1.7 tons (1.4–1.7 t/yd³)" at either allowance setting, although the volumes behind those lines are 0.97 and 1.02 cubic yards.
• The headline rounds to two decimals, which can flatter a near-miss. Spread over 77 sq ft at 4 inches the panel reports "1.00 cubic yards" beside "= 26.9 ft³", although a full cubic yard is 27.0 — the cubic-foot line is the one telling the truth.
• Excavation is not costed and not measured. Digging out 8 inches to lay 6 leaves you with spoil to remove, and this calculator neither sizes that nor prices it.
• The price field is forgiving in ways worth knowing. "$45" is read as 45, and so is "-45" — the minus sign is stripped rather than rejected. A malformed entry such as "45.5.5" is read as zero and the cost line simply disappears without comment.
• No fabric, no edging, no compaction equipment, no labor. The result is material volume and material cost, nothing else.
• It is not a substitute for a compaction test. The 5% and 10% figures are conventional allowances, not measured shrink factors for your specific stone on your specific subgrade.

Since every figure on this page is derived from the area, getting that first number right matters more than anything downstream of it. Irregular outlines and the unit conversions that come with them are handled in the Square Footage Calculator.

Two of these are worth acting on before anything is ordered: measure the area properly, and decide the depth on the traffic it will carry rather than on the budget. The rest are small, and they mostly push the same way — a real job needs slightly more than its rectangle suggests, and the panel is already leaning in that direction by 5% or 10%.