How to Calculate Gravel for a Driveway in 5 Simple Steps

Gravel for a driveway in one line

Gravel for a driveway is area times depth, converted to cubic yards, plus waste. A 20 ft by 12 ft driveway at 4 in deep holds 80 cubic feet of gravel; with 10% waste that is 88 cubic feet, or 3.26 cubic yards, or 4.56 tons. The rest of this guide is about getting those three inputs honest: the driveway size, the depth, and the waste allowance.

Step 1: Measure the driveway

Measure the length and the width in feet, edge to edge, at the widest points. The worked example is 20 ft long and 12 ft wide — a normal single driveway. Walk the tape down the middle, not along a curved edge, and if the driveway flares at the street, measure the flare as a second rectangle and add it later. A driveway that is 20 ft by 12 ft has an area of 240 square feet, and that one number is the foundation of everything that follows.

Step 2: Measure the depth, honestly

Depth is the input people guess worst, and it moves the answer more than any other input. Push a tape or a rod into the existing gravel in several places — middle, edges, wheel tracks — and average the readings. The worked example uses 4 in, a normal driveway depth. A path can manage 2 in, but a driveway that carries cars wants 4 in, and one that carries heavy vehicles wants 6 in. If the readings vary, use the average, not the deepest spot: the average is what the volume actually is.

Step 3: Work out the cubic feet

Multiply length by width by depth, with the depth in feet: 20 times 12 times 4 divided by 12, since there are 12 inches in a foot. That is 80 cubic feet. The division by 12 is the step people forget — multiplying 20 by 12 by 4 without it gives 960, which is twelve times too much, and that mistake has ordered many a second lorry load. Write the sum down: length times width times depth in inches, divided by 12, equals cubic feet.

Step 4: Convert to cubic yards, then add waste

Suppliers sell by the cubic yard, and there are 27 cubic feet in a cubic yard. Divide 80 by 27 and the bare order is 2.96 yards. Then add waste: 10% for spreading, settling and uneven ground takes 80 cubic feet to 88, and 88 divided by 27 is 3.26 yards. Waste is not padding — gravel settles into the sub-base, corners never spread evenly, and the last corner of a driveway without a waste allowance always comes up thin.

Step 5: Order by the yard or the ton

Order 3.26 cubic yards, or 4.56 tons at the usual 1.4 tons per cubic yard for crushed stone. If your supplier sells by the ton, confirm the tons-per-yard rate for your stone first: pea gravel weighs less per yard than crushed stone, and the same yards can mean different tons. Round the delivery up to the supplier’s nearest half yard — 3.5 yards here — which leaves a small pile for topping up the thin spots after the first rain. Keep that pile: it is the patch material for the wheel tracks.

Gravel in numbers

Suppose the driveway is 20 ft by 12 ft at 4 in deep, with 10% waste, at 1.4 tons per cubic yard. Area: 20 × 12 = 240 sq ft. Volume: 240 × 4 ÷ 12 = 80 cu ft. With waste: 80 × 1.10 = 88 cu ft. Cubic yards: 88 ÷ 27 = 3.26. Tons: 3.26 × 1.4 = 4.56. Order: 3.5 yards delivered, or 4.56 tons quoted.

Common mistakes

The most common mistake is forgetting to divide the depth by 12: inches and feet mixed in one sum give an answer twelve times too big. The second is measuring the depth at the deepest spot instead of averaging several readings, which over-orders. The third is skipping the waste allowance, which under-orders by exactly the amount the driveway settles. The fourth is ordering by tons using another stone’s density — the yards are the same, but the tons are not. The fifth is measuring the outside of the edging instead of the gravel area itself, which adds a border of gravel nobody spreads.

Worked example, start to finish

A driveway, 20 ft by 12 ft, 4 in deep, 10% waste, crushed stone at 1.4 tons a yard. Area: 240 sq ft. Volume: 80 cu ft. With waste: 88 cu ft. Yards: 3.26. Tons: 4.56. Result: order 3.5 yards delivered, spread 4 in deep, and keep the leftover pile for the wheel tracks after the first rain. If the same driveway were 6 in deep, the volume would be 120 cu ft and the order 4.89 yards, or 6.84 tons — depth alone would add more than half as much gravel again, which is why step two, measuring the depth honestly, matters most.

What changes the answer most

The depth changes the answer most: every extra inch adds a quarter of the volume again at 4 in, since depth multiplies the whole area. The driveway size is second: length and width move the area, but only across a delivery rounding does the lorry load change. The waste allowance is third: 10% is small beside depth, but it is the difference between a finished driveway and a thin last corner. The stone density is fourth, and it changes only the tons, never the yards. If the budget is tight, cut the depth on a path before cutting it on a driveway — never cut the waste allowance.

Frequently asked questions