How do you calculate the volume of a stockpile?
Match the pile to the nearest simple shape, measure it, and use that shape's formula. Tonnes are then volume × bulk density.
| Shape | Formula | Example |
|---|---|---|
| Cone | π × diameter² × height ÷ 12 | 10 m across, 3 m high: 78.5 m³ |
| Against a wall (half a cone) | π × width² × height ÷ 24 | 10 m along the wall, 3 m high: 39.3 m³ |
| Long ridge, rounded ends | ½ × width × height × (length − width) + π × width² × height ÷ 12 | 20 m long, 6 m wide, 2.5 m high: 128.6 m³ |
| Flat-topped | height ÷ 6 × (base area + top area + 4 × middle area) | Base 20 × 6 m, top 12 × 2 m, 3 m high: 200 m³ |
For the flat-topped pile, the middle area is the average length × the average width. For the long ridge, length is the full length of the pile, ends included.
How do I measure a pile by hand?
- The base. Walk a tape round the bottom of the pile. On a round pile, the distance round ÷ π gives the diameter, which is easier than trying to measure across it.
- The height. Stay on the ground. Use a laser rangefinder from a safe distance, or take an angle reading: height is your distance from the centre × the tangent of the angle, plus your eye height.
- Several rough shapes. Split a lumpy pile into simple shapes, work each one out, and add them up.
Do not climb a working stockpile. Loose material can give way underfoot, and the face can collapse.
How do I convert cubic metres to tonnes?
Multiply cubic metres by the material's bulk density in tonnes per cubic metre. 50 m³ of crushed rock at 1.60 t/m³ is 80 tonnes.
These are typical loose, stockpiled densities, the same ones the Stockpile app uses. Moisture can push them higher, especially in mulches. If the weight matters for a sale, use a weighbridge.
| Material | Typical t/m³ | Usual range |
|---|---|---|
| Crushed rock / road base | 1.60 | 1.45 to 1.85 |
| Crusher dust / screenings | 1.70 | 1.55 to 1.90 |
| River gravel (rounded) | 1.60 | 1.50 to 1.70 |
| Rail ballast | 1.55 | 1.45 to 1.65 |
| Recycled crushed concrete | 1.45 | 1.30 to 1.60 |
| Reclaimed asphalt (RAP) | 1.55 | 1.40 to 1.70 |
| Decorative pebble | 1.55 | 1.45 to 1.65 |
| Sand (dry) | 1.50 | 1.40 to 1.60 |
| Sand (damp / wet) | 1.80 | 1.70 to 2.00 |
| Topsoil (loose stockpile) | 1.30 | 1.20 to 1.40 |
| Fill dirt / subsoil | 1.60 | 1.50 to 1.75 |
| Clay (common) | 1.70 | 1.60 to 1.85 |
| Garden / landscape mix | 1.00 | 0.90 to 1.10 |
| Wood chip mulch | 0.30 | 0.20 to 0.40 |
| Bark mulch | 0.40 | 0.35 to 0.50 |
| Compost (screened) | 0.70 | 0.50 to 0.80 |
How accurate is a stockpile calculator?
It is only as good as the shape match and your measurements, so treat the answer as an estimate.
A neat cone from a conveyor can come out close. A pile pushed up by a loader, or one with hollows, a slumped side or a sloping floor, will not match any simple shape. Small errors matter too: the diameter is squared, so a pile measured a little too wide comes out noticeably too big.
When a shape will not do, measure the real surface instead. Stockpile measures a pile with your iPhone as you walk round it, and shows you what it did not see. For volumes that money or contracts depend on, use a licensed surveyor.