The gravel volume formula
Length times width times depth — three numbers, one multiplication, and two unit conversions where nearly every estimating error hides. Here is the formula with every trap flagged.
Contents
The volume formula
Volume (ft³) = Length (ft) × Width (ft) × Depth (ft)
- Length
- Longest side of the area (feet)
- Width
- Shorter side of the area (feet)
- Depth
- Gravel layer thickness — convert inches ÷ 12 first (feet)
Every dimension must be in the same unit before multiplying. The formula itself never changes — for circles, triangles and irregular shapes, only the area part changes (see the measurement guide).
This one line sizes every rectangular gravel job from a planter strip to a haul road. Everything that follows — yards, tons, cost — is unit conversion applied to its output. For non-rectangular sites, compute the area with the shape formulas in the measurement guide and multiply by depth exactly the same way.
The unit trap: inches are not feet
A 12 ft × 3 ft garden path with 3 inches of gravel.
- 1
Convert depth to feet
3 in ÷ 12 = 0.25 ft
- 2
Apply the formula
12 × 3 × 0.25 = 9 ft³
- 3
Sanity check
9 ft³ × 105 lb/ft³ = 945 lb ≈ half a ton — plausible for a small path
Result: 9 cubic feet. The sanity check — does the implied weight sound like this job? — catches unit errors before the supplier does.
Converting to cubic yards
Cubic yards = Cubic feet ÷ 27
- 27
- Cubic feet in one cubic yard (3 × 3 × 3) (ft³/yd³)
Divide by 27, not 9 (that's a square yard) and not 3 (a linear yard). Suppliers, truck capacities and most bulk prices all speak in cubic yards.
A 12 × 18 ft seating area with 3 inches of gravel — how many cubic yards?
- 1
Volume in cubic feet
12 × 18 × (3 ÷ 12) = 54 ft³
- 2
Divide by 27
54 ÷ 27 = 2.0 yd³
Result: 2 cubic yards — a small single-axle dump load. Most full-size dump trucks carry 10–14 yd³, pickup beds about 1 yd³ of gravel by weight limit.
From cubic yards to tons
Tons = Cubic yards × Density factor (t/yd³)
- 1.42
- Common gravel, loose (2,800 lb/yd³) (t/yd³)
- 1.30
- Pea gravel (2,600 lb/yd³) (t/yd³)
- 1.35
- #57 stone, loose (2,700 lb/yd³) (t/yd³)
- 1.69
- Crusher run, loose (3,375 lb/yd³) (t/yd³)
Density is where gravel type finally enters the math. Factors for every material are in the density chart and weight chart.
The same 12 × 18 ft seating area, ordered in tons of common gravel with a 10% allowance.
- 1
Volume
12 × 18 × 0.25 = 54 ft³ = 2.0 yd³
- 2
Convert to tons
2.0 × 1.42 = 2.84 tons
- 3
Add 10% allowance
2.84 × 1.10 = 3.12 tons
- 4
Round to the ordering increment
3.12 → 3.5 tons (half-ton increments)
Result: Order 3.5 tons. Four short steps take you from a tape measure to a phone order — and each one is checkable.
If a quote arrives in the other unit, the conversion runs both ways: tons ÷ 1.42 = loose cubic yards. The weight chart covers every direction of this conversion, and the coverage guide translates the result into square feet on the ground.
The metric shortcut
Tonnes = L (m) × W (m) × D (m) × Density (t/m³)
- D
- Depth in meters — 75 mm = 0.075 m (m)
- Density
- 1.68 for common gravel, 1.54 pea, 2.00 crusher run loose (t/m³)
No 12, no 27, no 2,000. One multiplication chain from tape measure to order weight.
Formula questions
Let the calculator run the chain
Volume, yards, tons and bags from your dimensions — with the right density for every gravel type built in.
Go deeper
Sources & references
- [1]ASTM C29/C29M: Bulk Density (Unit Weight) and Voids in Aggregate — ASTM International, 2017
- [2]The Aggregates Handbook, 2nd ed. — National Stone, Sand & Gravel Association, 2013