The short answer
One brass is 100 cubic feet, which is 2.83 cubic metres. One cubic metre is 35.31 cubic feet. To turn a volume into weight, multiply by the loose bulk density of the material: about 1.5 to 1.6 tonnes per cubic metre for 20 mm aggregate, so one brass of 20 mm weighs roughly 4.2 to 4.5 tonnes.
Stone is quoted by the brass in Maharashtra and Gujarat, by the cubic foot across much of the north, by the cubic metre in bills of quantities and by the tonne over a weighbridge. A buyer on a highway package can meet all four in one week. The conversions are simple once volume and weight are kept apart.
01Volume to volume
| Unit | Cubic feet | Cubic metres | Brass |
|---|---|---|---|
| 1 brass | 100 | 2.832 | 1 |
| 1 cubic metre | 35.31 | 1 | 0.353 |
| 1 cubic foot | 1 | 0.0283 | 0.01 |
| 100 cubic metres | 3,531 | 100 | 35.3 |
02Volume to weight
There is no fixed number of tonnes in a brass, because a brass is a volume and each material packs differently. The link is loose bulk density: the weight of stone that fills a cubic metre when tipped in without compaction.
| Material | Loose density, t/m3 | Tonnes per brass | Cubic feet per tonne |
|---|---|---|---|
| 40 mm aggregate | 1.45 to 1.55 | 4.1 to 4.4 | 23 to 24 |
| 20 mm aggregate | 1.50 to 1.60 | 4.2 to 4.5 | 22 to 24 |
| 10 mm aggregate | 1.45 to 1.55 | 4.1 to 4.4 | 23 to 24 |
| Crusher dust | 1.45 to 1.75 | 4.1 to 5.0 | 20 to 24 |
| GSB, loose | 1.70 to 1.85 | 4.8 to 5.2 | 19 to 21 |
| WMM, loose | 1.75 to 1.90 | 5.0 to 5.4 | 19 to 20 |
| Boulder, as loaded | 1.60 to 1.70 | 4.5 to 4.8 | 21 to 22 |
Typical values for crushed basalt and granite. Lighter rock such as sandstone runs lower, and dust varies most of all with moisture. Measure your own: fill a box of known volume, strike it level and weigh it.
03Loose is not compacted
The figures above are for stone in a truck or a stockpile. Once GSB or WMM is laid and rolled it is far denser, about 2.2 to 2.3 tonnes per cubic metre for GSB and 2.25 to 2.4 for WMM. A bill of quantities measures the compacted layer. A truck carries loose material. Mixing the two is the commonest error in ordering.
- BOQ quantity, compacted
- 500 m3
- Compacted density
- 2.25 t/m3
- Weight to order
- 1,125 t
- Loose volume at 1.78 t/m3
- 632 m3
- In brass
- 223 brass
- Loads at 18 t each
- 63
The same 500 cubic metres on the drawing is 632 cubic metres in tippers. An order placed as "500 cubic metres" without saying which will arrive a fifth short.
04Why tonnes settle arguments
- A truck body can be loaded level, heaped or short, and nobody measures it at the gate.
- Loose stone settles on the road. A load that left full arrives looking light.
- Damp fines bulk. Crusher dust and sand at a few per cent moisture take up noticeably more volume than the same material dry.
- A weighbridge gives one number, printed, that both sides can check against a second bridge.
Volume is fine for estimating. Payment is better made on weight. How a weighbridge slip is read and reconciled is in weighbridge slips, and what the trucks themselves hold is in tipper capacity.
05Checking a truck by its body
Where there is no bridge, measure the inside of the tipper body in metres: length times width times the height of the load. A body 5.5 m long, 2.3 m wide and loaded 1.0 m deep holds about 12.6 cubic metres, which is 4.5 brass, or a little under 20 tonnes of 20 mm at 1.55. It is a check, not a measurement. A heaped load carries more, and a load that has travelled 40 km will have settled.