Gravel Calculator

How much gravel do I need? The arithmetic behind the number

Every gravel order comes down to one calculation: area multiplied by depth, converted into cubic yards, then converted again into tons because that is how most quarries sell. Measure the length and the width in feet, turn the depth from inches into feet by dividing by twelve, multiply the three together for cubic feet, then divide by 27 because a cubic yard holds 27 cubic feet. Multiply the yardage by the density of the stone and divide by 2,000 to get US short tons.

Worked example: a 30 ft by 12 ft driveway

A typical single-car drive is 30 ft long and 12 ft wide, so the area is 360 square feet. Spreading 3 in of crushed stone means 360 x 0.25 ft = 90 cubic feet, which is 90 / 27 = 3.33 cubic yards. At 2,800 lb per cubic yard that load weighs 9,333 lb, or 4.67 tons. Ask the yard for 3.7 cubic yards or 5.1 tons and the extra ten percent covers the settling. For comparison, that same 3.33 yards would take 180 bags of the 0.5 cubic foot size sold at hardware stores, which is why loose delivery wins on anything but a repair patch.

Building the same drive from scratch

A brand new driveway is not one 3 in layer, it is roughly 8 in of stone in three courses. Over the same 360 square feet that is 360 x 0.667 ft = 240 cubic feet, or 8.9 cubic yards, about 12.4 tons. Ordering only the top course for a new build is the most common mistake this calculator prevents: run it once per layer and add the results.

The three-layer driveway system

Contractors in the US build gravel drives in graded lifts, each doing a different job.

Base course: #2 or crusher run, about 4 in

Large angular stone, roughly golf-ball sized, laid straight on compacted subgrade over a geotextile fabric. It carries the load and lets water move. For the example drive that is 4.4 cubic yards, about 6.2 tons.

Middle course: #57, about 2 in

Clean, roughly one-inch angular stone that locks into the voids of the base. 2.2 cubic yards, or about 3.1 tons for the example. In the UK the closest equivalents are MOT Type 1 for the base and 20 mm clean for the middle.

Top course: crushed stone with fines, 2 to 3 in

Small crushed stone with dust in it, so it binds and holds a smooth surface. This is the only layer that gets replaced periodically, typically every three to five years on a used drive. Decorative pea gravel and river rock belong here only on paths and patios, never on a drive that gets turning traffic, because rounded stone will not lock together.

Why the compaction margin matters

Loose stone dropped from a truck occupies more space than the same stone raked flat and rolled with a plate compactor. The difference is typically 5 to 10 percent for angular material, and a little less for rounded gravel. Because you cannot order 0.4 of a load a second time without paying a second delivery fee, always round the padded number up to the next practical quantity your supplier sells. Being half a ton over is a wheelbarrow of spare stone; being half a ton short is another minimum-charge trip.

What this calculator does not cover

Densities here are averages for dry material: crushed stone at 2,800 lb per cubic yard, pea gravel 2,600, river rock 2,700 and decomposed granite 3,000. Wet stone can weigh 10 to 15 percent more, which changes a weight-priced delivery but not the volume you need. The maths also assumes a rectangle of even depth. For an L-shaped drive, split it into rectangles and run each one; for a circle, use pi times the radius squared as the area; for a ditch or French drain, use the trench length times its width. Sloped ground, ruts and soft spots all swallow extra stone, so measure the deepest point rather than the average if the surface is uneven.