Gravel is the workhorse of outdoor projects — driveways, paths, patio bases, and drainage all start with it. The catch is that it is sold two different ways, by the cubic yard and by the ton, which is where most estimates go wrong. The math itself is the same volume calculation you would use for any aggregate, plus one conversion to tons. This guide covers the formula, how deep to go and which stone to use for each job, and the order math once you factor in waste and compaction.
The formula (plus the tons step)
Gravel volume is length x width x depth, in feet, converted to cubic yards — then one extra step to tons:
- Measure length and width in feet, and convert depth from inches to feet (inches ÷ 12).
- Multiply the three for cubic feet.
- Divide by 27 for cubic yards.
- Multiply by the density, about 1.4 tons per cubic yard, to get tons (the range is 1.4–1.7 depending on the stone).
There is a useful shortcut if you already know your area in square feet: (square feet x depth in inches) ÷ 324 = cubic yards. Either way, a 30 ft x 12 ft driveway at 4 inches comes to 30 x 12 x 0.33 = about 120 cubic feet → 4.44 cubic yards → roughly 6.2 tons.
Step by step
- Measure length and width in feet, and choose a depth for the job.
- Convert to cubic yards with ÷ 27, or use the ÷ 324 area shortcut.
- Convert to tons (x 1.4) if your supplier sells by weight.
- Add about 10% for waste and compaction before you order.
How deep should it go?
Depth is set by the load the gravel will carry:
- Paths, walkways, decorative beds: 2–3 inches.
- Driveways (light vehicles): 4 inches; 6 inches for heavy use or soft ground.
- Patio and paver bases: 4–6 inches, compacted — the same base you would put under a concrete slab.
- Drainage and French drains: 2–4 inches to fill the trench.
Whatever the depth, excavate 1–2 inches deeper than the finished surface. Gravel compacts as it settles and gets driven on, and if you do not account for that the surface ends up low.
Cubic yards, tons, and coverage
Gravel weighs about 1.4 tons per cubic yard, ranging from 1.4 to 1.7 depending on stone size, type, and moisture. Convert yards to tons by multiplying by 1.4, and tons back to yards by dividing by 1.4. How far a load goes depends entirely on depth:
- 1 ton covers about 100 sq ft at 2 inches, or about 60 sq ft at 4 inches.
- 1 cubic yard covers about 160 sq ft at 2 inches, or about 80 sq ft at 4 inches.
Which gravel for which job
Not all gravel is interchangeable — using the wrong type leads to drainage problems or an unstable surface:
- Crusher run / road base (#411): crushed stone mixed with fine "fines" that lock together when compacted. This is the base layer for driveways, patios, and under pavers.
- #57 stone (about 3/4 inch): angular and free-draining; it does not pack tight, which makes it the surface layer of driveways and the fill for French drains.
- Pea gravel (about 3/8 inch, smooth and rounded): ideal for paths, patios, and decorative beds — but it shifts under tires, so it is a poor sole driveway surface.
- Larger #2 / #3 stone: a deep sub-base for soft or wet ground.
A typical gravel driveway is a compactable base topped with a drainable surface — crusher run packed down, #57 on top.
Odd shapes: circles, triangles, and L-shapes
The same decomposition works for any footprint: split an L-shape into rectangles and add the volumes; a circle is π x radius² x depth; a triangle is ½ x base x height x depth.
Add for waste and compaction
Order about 10% extra. Some gravel is lost transferring it from the truck, some shifts, and compaction pulls the surface down — which is also why you over-excavate by 1–2 inches. For the 30 x 12 driveway: 6.2 tons + 10% ≈ 6.8, so you would order about 7 tons.
A full worked example
A 30 ft x 12 ft gravel driveway at 4 inches:
- Volume: 30 x 12 x 0.33 = ~120 cu ft → 4.44 cubic yards
- Weight: 4.44 x 1.4 ≈ 6.2 tons
- With 10%: order about 7 tons (≈ 5 cubic yards) — a crusher-run base topped with #57.
Common mistakes to avoid
- Forgetting the tons conversion when the supplier prices by weight.
- Not over-excavating for compaction, leaving a sunken surface.
- Using smooth pea gravel as a driveway surface.
- Skipping the 10% margin for waste and settling.
- Spreading too thin to stretch a load — it scatters and exposes the base.
Measure in feet, convert to cubic yards, add the tons step if you are buying by weight, and finish with a 10% cushion. Match the depth and the stone to the job, and your load will go exactly as far as it should.