“Earth is an oblate spheroid shaped by gravity and rotation, with an equatorial radius of 6,378 kilometers and a polar radius of 6,356 kilometers.”

• NASA's NSSDC Earth Fact Sheet lists Earth's equatorial radius as 6,378.137 km and polar radius as 6,356.752 km — matching the claim's figures when rounded to the nearest kilometer.
• The WGS-84 reference ellipsoid (the global standard used by GPS, maintained by the U.S. National Geospatial-Intelligence Agency) defines a semi-major (equatorial) axis of 6,378,137 m and a derived semi-minor (polar) axis of ~6,356,752.3 m, i.e. a flattening of about 1/298.257.
• The physical mechanism stated is correct and standard: Earth's ~24-hour rotation produces a centrifugal effect greatest at the equator, and in combination with self-gravitation (hydrostatic equilibrium of a rotating fluid-like body) this yields an equatorial bulge of roughly 21-22 km — exactly the difference between the two quoted radii.
• 'Oblate spheroid' (ellipsoid of revolution flattened at the poles) is the terminology used by NASA, NOAA, USGS and standard geodesy texts to describe Earth's gross figure.
• Independent measurement methods — satellite laser ranging, GRACE/GRACE-FO gravimetry, VLBI and GNSS geodesy — all converge on the same flattening value, so the numbers are not dependent on a single technique.
• The claim's rounding is conservative and non-misleading: 6,378 and 6,356 km are the accepted textbook roundings, and the implied 22 km difference is within a kilometer of the precise 21.4 km.

• Strictly, Earth's true shape is the geoid (an equipotential surface of the gravity field), which departs from the best-fit ellipsoid by roughly ±100 m due to density heterogeneity, mantle convection and post-glacial rebound; 'oblate spheroid' is an excellent approximation, not an exact description.
• Topography is not captured: the surface ranges from Mount Everest (~8.8 km above sea level) to the Challenger Deep (~10.9 km below), and the point farthest from Earth's centre is Chimborazo, not Everest — though these deviations are tiny relative to the 6,378 km radius.
• There is a small triaxiality (equatorial radii differ by roughly 70-200 m depending on the model), so 'spheroid' is a slight idealisation of an ellipsoid with three unequal axes.
• The quoted radii are rounded reference-ellipsoid values, not direct physical measurements of any particular point on the ground; the polar radius is more precisely ~6,356.75 km and the equatorial ~6,378.14 km.
• The phrase 'shaped by gravity and rotation' omits secondary shaping influences (tidal interaction with the Moon and Sun, mantle dynamics, ice-mass redistribution), though none of these alter the dominant explanation.

97/100 — the lab’s own confidence in the score above, not a second reading of the claim.

NASA Goddard Space Flight Center — National Space Science Data Centergov · 98 · NASA Science — Earth Factsgov · 96 · NOAA National Ocean Servicegov · 95 · NOAA National Geodetic Surveygov · 95 · Encyclopaedia Britannicaother · 85

• NASA lists Earth’s shape as an oblate spheroid and gives an equatorial radius of 6,378.137 km and polar radius of 6,356.752 km, which round to the 6,378 km and 6,356 km stated in the claim.
• NOAA explains that Earth is not a perfect sphere: it is slightly flattened at the poles and bulges at the equator, consistent with an oblate spheroid caused by rotation acting with gravity.
• The stated equatorial radius being larger than the polar radius by about 22 km matches the accepted geodetic model of Earth’s flattening.

• The claim is slightly simplified: Earth’s actual physical shape is irregular and often modeled more precisely as a geoid or reference ellipsoid, not a perfect oblate spheroid.
• The polar radius is more accurately about 6,356.752 km, so rounding to 6,356 km is slightly low if rounded to the nearest kilometer; 6,357 km would be the conventional nearest-kilometer rounding.

98/100 — the lab’s own confidence in the score above, not a second reading of the claim.

NASAgov · 98 · NOAA National Ocean Servicegov · 96 · NOAA National Geodetic Surveygov · 95

• Geodetic measurements and satellite data confirm that Earth is not a perfect sphere, but an oblate spheroid. This shape is the direct result of Earth's gravity pulling matter inward while its rotation creates a centrifugal force that causes a bulge at the equator.
• According to the World Geodetic System (WGS 84) and NASA's planetary fact sheets, Earth's equatorial radius is approximately 6,378.1 kilometers.
• The polar radius is measured at approximately 6,356.8 kilometers. The numbers in the claim (6,378 km and 6,356 km) are highly accurate and represent standard accepted rounded measurements for Earth's dimensions.

• There is no scientifically valid evidence against the fundamental claim. On a strictly pedantic level, Earth's exact shape is known as a 'geoid' because it is slightly irregular due to uneven mass distribution (mountains, trenches). Additionally, the polar radius of 6,356.8 km is sometimes rounded to 6,357 km rather than 6,356 km, but this is a trivial rounding difference.

100/100 — the lab’s own confidence in the score above, not a second reading of the claim.

NASA Goddard Space Flight Centergov · 100 · National Oceanic and Atmospheric Administration (NOAA)gov · 100

• Earth is conventionally modeled in geodesy as an oblate spheroid or ellipsoid of revolution: its radius is larger at the equator than at the poles.[https://geodesy.noaa.gov/geopotential-datums/geopotential-surface.shtml]
• NASA gives the equatorial radius as approximately 6,378 km and the polar radius as approximately 6,357 km, closely matching the claim’s 6,378 km and 6,356 km figures.[https://imagine.gsfc.nasa.gov/features/cosmic/earth_info.html]
• The difference between the equatorial and polar radii is produced by Earth’s rotation, while gravity contributes to the equilibrium shape of a rotating planet; NASA describes Earth as approximately an oblate spheroid.[https://ntrs.nasa.gov/api/citations/19770020703/downloads/19770020703.pdf]
• The WGS 84 reference ellipsoid specifies a semi-major (equatorial) axis of 6,378,137 meters, which rounds to 6,378 km.[https://earth-info.nga.mil/index.php?dir=wgs84&action=wgs84]

• The exact polar radius depends on the reference ellipsoid used. For WGS 84, NOAA gives a polar radius of 6,356,752.3141 meters, or about 6,356.75 km, rather than exactly 6,356 km.[https://geodesy.noaa.gov/PC_PROD/Inv_Fwd/readme.htm]
• Earth’s physical surface is not a perfect oblate spheroid: topography and variations in the gravity field produce an irregular geoid. The oblate spheroid is an idealized mathematical approximation.[https://geodesy.noaa.gov/geopotential-datums/geopotential-surface.shtml]
• The wording attributes the shape broadly to gravity and rotation but does not specify a reference system or explain that the measured figure varies slightly by adopted geodetic model.

97/100 — the lab’s own confidence in the score above, not a second reading of the claim.

NASAgov · 97 · National Geospatial-Intelligence Agencygov · 99 · National Geodetic Survey, NOAAgov · 98 · NASA Technical Reports Servergov · 94

• Satellite geodesy, VLBI, GPS, and laser ranging measure an equatorial bulge of ~21 km produced by rotation under self-gravity.
• NASA's Earth fact sheet lists equatorial radius 6378.137 km and polar radius 6356.752 km, matching the claim's rounded kilometer values.
• A self-gravitating fluid body in hydrostatic equilibrium rotating at Earth's sidereal rate is an oblate spheroid; this is the standard first-order model (WGS 84 / GRS 80).

• Polar radius 6356.752 km conventionally rounds to 6357 km rather than 6356 km.
• The physical surface and geoid deviate from a perfect ellipsoid by tens to hundreds of meters (topography and density anomalies), so 'oblate spheroid' is an approximation.

92/100 — the lab’s own confidence in the score above, not a second reading of the claim.

NASAgov · 95