Earth Equatorial Radius
| Value | 6,378,137 m |
| Status | Exact by definition — no uncertainty |
| Source | WGS 84 defining parameter |
| Categories | Astronomical |
| Planck length | 3.9462442e+41 lP |
| femtometer | 6.3781370e+21 fm |
| picometer | 6.3781370e+18 pm |
| bohr radius | 1.2052932e+17 a0 |
| angstrom | 6.3781370e+16 Å |
| nanometer | 6.3781370e+15 nm |
| micrometer | 6,378,137,000,000 μm |
| thou | 251,107,760,000 thou |
| point | 18,079,758,000 pt |
| millimeter | 6,378,137,000 mm |
| pica | 1,506,646,500 pc |
| centimeter | 637,813,700 cm |
| inch | 251,107,760 in |
| decimeter | 63,781,370 dm |
| hand | 62,776,939 hh |
| link | 31,705,525 li |
| foot | 20,925,646 ft |
| US survey foot | 20,925,604 ftUS |
| yard | 6,975,215.4 yd |
| meter | 6,378,137 m |
| fathom | 3,487,607.7 ftm |
| rod | 1,268,221 rd |
| chain | 317,055.25 ch |
| cable length | 34,439.185 cb |
| furlong | 31,705.525 fur |
| kilometer | 6,378.137 km |
| mile | 3,963.1906 mi |
| nautical mile | 3,443.9185 nmi |
| league | 1,321.0635 lea |
| megameter | 6.378137 Mm |
| Earth radius | 1.0011202 REarth |
| light-second | 0.021275175 ls |
| lunar distance | 0.016592491 LD |
| solar radius | 0.0091679416 Rsun |
| light-minute | 0.00035458625 lmin |
| astronomical unit | 0.000042635212 AU |
| light-year | 6.7416961e-10 ly |
| parsec | 2.0670134e-10 pc |
| kiloparsec | 2.0670134e-13 kpc |
| megaparsec | 2.0670134e-16 Mpc |
| gigaparsec | 2.0670134e-19 Gpc |
Learning zone
Earth's spin makes it an oblate spheroid: the equator bulges 21 km beyond the poles, so a mountain in Ecuador can be farther from the planet's centre than Everest is. Newton predicted the flattening from rotation in the Principia; the French Geodesic Missions to Lapland and Peru in the 1730s measured the length of a degree of latitude at both ends of the world and confirmed him against Cassini's rival prolate model.
The value here is a defining constant of the World Geodetic System 1984, not a measurement — the ellipsoid is fixed by convention so that coordinates are reproducible, and everything else about it (the polar radius, the mean radius, the flattening ratio 1/298.257223563) is derived arithmetic. Every GPS fix on Earth is expressed relative to this surface.