A barrel is one of several units of volume applied in various contexts; there are dry barrels, fluid barrels (such as the UK beer barrel and US beer barrel), oil barrels and so on. For historical reasons the volumes of some barrel units are roughly double the volumes of others; volumes in common usage range from about 100 to 200 litres (22 to 44 imp gal; 26 to 53 US gal). In many connections the term "drum" is used almost interchangeably with "barrel".
| Definition | Relation to SI units |
|---|---|
≡ 36 gal (imp) |
| US legal cup | pipe | drop (imperial) | pony | imperial minim | fluid scruple | petaliter | hectoliter |
|---|---|---|---|---|---|---|---|
| 1 | 0.0005032 | 2,432.6839108 | 10.8204873 | 4,054.4731847 | 202.7236592 | 2.4 × 10-16 | 0.0024 |
| 1,987.3411866 | 1 | 4,834,572.929895 | 21 504 | 8,057,621.5498223 | 402,881.0774932 | 4.76961884784 × 10-13 | 4.7696188 |
| 0.0004111 | 2.0684350293206 × 10-7 | 1 | 0.0044480 | 1.6666667 | 0.0833333 | 9.86564670138 × 10-20 | 9.86564670138 × 10-7 |
| 0.0924173 | 4.6502976190476 × 10-5 | 224.8220299 | 1 | 374.7033831 | 18.7351692 | 2.2180147171875 × 10-17 | 0.0002218 |
| 0.0002466 | 1.2410610175928 × 10-7 | 0.6000000 | 0.0026688 | 1 | 0.0500000 | 5.91938802083 × 10-20 | 5.91938802083 × 10-7 |
| 0.0049328 | 2.482122035173 × 10-6 | 12.0000000 | 0.0533756 | 20.0000000 | 1 | 1.18387760416 × 10-18 | 1.18387760416 × 10-5 |
| 4.1666666666667 × 1015 | 2 096 603 590 144 | 1.0136182961631 × 1019 | 4.5085363602457 × 1016 | 1.6893638269379 × 1019 | 8.4468191347325 × 1017 | 1 | 10 000 000 000 000 |
| 416.6666667 | 0.2096604 | 1,013,618.2961631 | 4,508.5363602 | 1,689,363.8269379 | 84,468.1913473 | 1.0 × 10-13 | 1 |
| Symbol | Definition |
|---|---|
| ≡ | exactly equal |
| ≈ | approximately equal to |
| = | equal to |
| digits | indicates that digits repeat infinitely (e.g. 8.294 369 corresponds to 8.294 369 369 369 369 …) |
| 1 imperial barrels | = 0.16365924 cubic meters |
| 2 imperial barrels | = 0.32731848 cubic meters |
| 3 imperial barrels | = 0.49097772 cubic meters |
| 4 imperial barrels | = 0.65463696 cubic meters |
| 5 imperial barrels | = 0.8182962 cubic meters |