Earth Mean Radius
| Value | 6371008.8 m |
| Status | Conventional / typical value |
| Source | IUGG mean radius R₁ of the WGS 84 ellipsoid |
| Categories | Astronomicalearthgeodesy |
R_earth in every length unit
| femtometer | 6.3710088e+21 fm |
| picometer | 6.3710088e+18 pm |
| nanometer | 6.3710088e+15 nm |
| micrometer | 6,371,008,800,000 μm |
| millimeter | 6,371,008,800 mm |
| centimeter | 637,100,880 cm |
| decimeter | 63,710,088 dm |
| meter | 6,371,008.8 m |
| kilometer | 6,371.0088 km |
| inch | 250,827,120 in |
| foot | 20,902,260 ft |
| yard | 6,967,419.9 yd |
| mile | 3,958.7613 mi |
| nautical mile | 3,440.0695 nmi |
| astronomical unit | 0.000042587563 AU |
| light-year | 6.7341616e-10 ly |
| parsec | 2.0647033e-10 pc |
Learning zone
Eratosthenes got here first, around 240 BC: knowing the Sun stood directly over a well in Syene at midsummer noon while casting a 7.2° shadow in Alexandria, he scaled the distance between the cities up by 360/7.2 and obtained a circumference within a few per cent of the truth. His method needed no instrument more exotic than a stick.
The modern mean radius is a convenience rather than a physical boundary: it is the IUGG arithmetic mean of the ellipsoid's three semi-axes, and the real solid surface departs from it by nearly 9 km at Everest and 11 km in the Mariana Trench. Use it for escape velocity, surface gravity and great-circle distances; use the equatorial or polar radius when the 21 km difference matters.