Earth Polar Radius
| Value | 6356752.314245 m |
| Status | Exact by definition — no uncertainty |
| Source | WGS 84, derived exactly from the defining semi-major axis and flattening |
| Categories | Astronomicalearthgeodesy |
| femtometer | 6.3567523e+21 fm |
| picometer | 6.3567523e+18 pm |
| nanometer | 6.3567523e+15 nm |
| micrometer | 6,356,752,300,000 μm |
| millimeter | 6,356,752,300 mm |
| centimeter | 635,675,230 cm |
| decimeter | 63,567,523 dm |
| meter | 6,356,752.3 m |
| kilometer | 6,356.7523 km |
| inch | 250,265,840 in |
| foot | 20,855,487 ft |
| yard | 6,951,828.9 yd |
| mile | 3,949.9028 mi |
| nautical mile | 3,432.3717 nmi |
| astronomical unit | 0.000042492265 AU |
| light-year | 6.7190925e-10 ly |
| parsec | 2.0600831e-10 pc |
Learning zone
The polar radius is not measured independently; it follows exactly from the two WGS 84 defining constants as b = a(1 − f), with the flattening f = 1/298.257223563. The 21.4 km difference from the equatorial radius is the centrifugal bulge, and it is why sea level, orbital mechanics and map projections all need an ellipsoid rather than a sphere. Anyone quoting a single "radius of the Earth" is quietly choosing an average.
The oblateness has consequences beyond geometry. Its gravitational signature, the J₂ term, torques satellite orbits into a slow precession; mission designers exploit this deliberately to fly sun-synchronous orbits whose planes rotate once a year, so an imaging satellite crosses every latitude at the same local solar time on every pass.