chain
Lengthexact by definition
A chain is exactly 66 feet, 22 yards, or 20.1168 metres. It is the unit the American landscape is laid out in: ten square chains make an acre exactly, eighty chains make a mile, and the Public Land Survey System's section corners were set by dragging one.
Watch out: A cricket pitch is one chain long, which is the easiest way to picture it. Engineers' chains of 100 ft also existed and appear in older railway and highway stationing, so a chainage figure from an old drawing needs its chain identified.
| 1 | 20.1168 |
Edmund Gunter designed it around 1620 to reconcile two incompatible systems. At 66 ft it is a whole number of the traditional units and, because it holds 100 links, it also decimalises cleanly. That single compromise is why an acre is 43,560 ft² rather than something round.
One chain in every length unit
| 1.24466e+36 | Planck length (lP) | |
| 2.01168e+16 | femtometer (fm) | |
| 20,116,800,000,000 | picometer (pm) | |
| 380,152,000,000 | bohr radius (a0) | |
| 201,168,000,000 | angstrom (Å) | |
| 20,116,800,000 | nanometer (nm) | |
| 20,116,800 | micrometer (μm) | |
| 792,000 | thou (thou) | |
| 57,024 | point (pt) | |
| 20,116.8 | millimeter (mm) | |
| 4,752 | pica (pc) | |
| 2,011.68 | centimeter (cm) | |
| 792 | inch (in) | |
| 201.168 | decimeter (dm) | |
| 198 | hand (hh) | |
| 100 | link (li) | |
| 66 | foot (ft) | |
| 65.9999 | US survey foot (ftUS) | |
| 22 | yard (yd) | |
| 20.1168 | meter (m) | |
| 11 | fathom (ftm) | |
| 4 | rod (rd) | |
| 1 | chain (ch)this unit | |
| 0.108622 | cable length (cb) | |
| 0.1 | furlong (fur) | |
| 0.0201168 | kilometer (km) | |
| 0.0125 | mile (mi) | |
| 0.0108622 | nautical mile (nmi) | |
| 0.00416667 | league (lea) | |
| 0.0000201168 | megameter (Mm) | |
| 0.00000315756 | Earth radius (REarth) | |
| 6.71024e-08 | light-second (ls) | |
| 5.23331e-08 | lunar distance (LD) | |
| 2.89159e-08 | solar radius (Rsun) | |
| 1.11837e-09 | light-minute (lmin) | |
| 1.34473e-10 | astronomical unit (AU) | |
| 2.12635e-15 | light-year (ly) | |
| 6.51941e-16 | parsec (pc) | |
| 6.51941e-19 | kiloparsec (kpc) | |
| 6.51941e-22 | megaparsec (Mpc) | |
| 6.51941e-25 | gigaparsec (Gpc) |