“Look closely: **Earth's shape and size aren't as constant as they seem.** At a given point in time, Earth usually seems stable. But over centuries, lands rise and sink, continents move and the balance of the ocean shifts. **These changes are tracked through the science of geodesy, dedicated to measuring and precisely charting the size and shape of Earth.**” This NOAA educational page emphasizes that Earth's size and shape vary and must be measured, implying it is not a perfect, fixed sphere.

NASA describes geodesy as “the study of the shape of the Earth.” The text notes that **“The Earth is not a perfect shape and is constantly changing. Only through a very carefully constructed system of analysis can scientists achieve the necessary accuracy about the planet's shape (the so-called 'geoid') to make measurements of sea level from space.”** This explicitly states Earth is not a perfect shape, contradicting the idea of a perfect sphere.

NASA defines geodetics (geodesy) as “the science of studying **Earth’s shape, gravity and its effect** on phenomena such as polar motion, waterbody tides, and tectonic motion in three-dimensional space over time.” It explains that geodetic data are used for “tracking **variations in ocean topography**” and crustal dynamics, underscoring that Earth’s shape and surface are not perfectly spherical but vary over space and time.

In its overview on oblate spheroids, ScienceDirect states: "Earth is an oblate spheroid." It further notes that Earth is composed of different layers in spherical shells as determined by drilling and seismic evidence, indicating that while roughly spherical in layering, the overall figure is an oblate spheroid rather than a perfect sphere.

National Geographic reports that the new gravity map “is referred to as a **geoid**” and that people usually picture Earth as “a fairly smooth sphere. **However, the distribution of matter is uneven** [on] the planet surface, [and] bodies of [water] are in continual flux due to both winds and currents.” By measuring gravity, “the geoid shows the shape that mean sea level would have if it could be extended across the world,” revealing a **‘lumpy’ Earth** rather than a perfect sphere.

ESA explains that the visualization “shows how the **geoid represents deviations from the Earth's ellipsoid.** Although it has ‘highs’ and ‘lows’ – it is a surface of equal gravitational potential.” The very need to describe Earth with an ellipsoid and a geoid of “highs” and “lows” indicates that Earth does not have a perfect spherical shape, but a more complex, uneven form determined by rotation and mass distribution.

The planet Earth has a rather slight equatorial bulge; its equatorial diameter is about 43 km (27 mi) greater than its polar diameter, with a difference of about 1/298 of the equatorial diameter. In the WGS-84 standard Earth ellipsoid, widely used for map-making and the GPS system, Earth's radius is assumed to be 6,378.137 km to the Equator and 6,356.7523142 km to either pole, meaning a difference of 21.3846858 km between the radii or 42.7693716 km between the diameters, and a relative flattening of 1/298.257223563.

In a public explanation of its GRACE geoid model, NASA states: “**The geoid is a scientific model that reveals Earth's true gravitational shape. Rather than being a perfect sphere, our planet has subtle bumps …**” This description from NASA explicitly contrasts the real gravitational shape of Earth with a perfect sphere, highlighting small but real deviations.

Earth's shape is not a perfect sphere; it is classified as an oblate spheroid, meaning it is slightly flattened at the poles and bulging at the equator. The Earth's equatorial diameter is approximately 12,756 kilometers, while its polar diameter is about 12,714 kilometers, resulting in an oblateness value of around 0.00336 (about one part in 298). Because of the equatorial bulge, objects at sea level at the equator are about 21 kilometers farther from the center of Earth than if they were at sea level at either pole.

Earth might look like a sphere, but it’s actually an "oblate spheroid" — the planet is slightly squished, making the circumference of the equator bigger than the circumference through the poles. As a result, a person on the equator is over 13 miles farther from Earth’s center than a person on the North Pole is. That difference is more than double the distance between sea level and the top of Mount Everest, but on a planetary scale, this bulge is virtually imperceptible.

Earth is described as an oblate spheroid rather than a perfect sphere. That means it is wider in the middle and flatter at the poles. The page gives an equatorial diameter of about 12,756 km and a polar diameter of about 12,714 km.

The lesson explicitly states: "The Earth is not a perfect sphere. Because it is spinning, it 'bulges' at the middle. This makes the Earth a 'squished sphere,' or 'oblate spheroid.'" It explains that due to this bulging, "the difference between the diameter of the earth at the equator and the poles is about 42 kilometers," even though the overall diameter is over 12,000 kilometers.

According to Newtonian mechanics the spinning of a planet on its axis should cause it to bulge at the equator. The best modern measurements of the Earth's actual equatorial bulge give the currently accepted value of about 21,476 meters (which is 1 part in 297.0). One of the first confirmations of the equatorial bulge was the observation that pendulum clocks run about 2.5 minutes slower per day near the equator than at higher latitudes, reflecting the change in gravity and distance from Earth’s center.

Earth's equatorial radius is 6,378.14 km and Earth's polar radius is 6,356.75 km. The page also notes that the polar radius is about 99.66% of the equatorial radius, which reflects Earth's slight flattening at the poles.

An oblate spheroid is a sphere-like shape that appears flattened at the top and bottom so that the circumference around the poles is less than the circumference around the equator. The article states: "The Earth is an oblate spheroid" and notes that the difference between a perfect sphere and Earth's shape is small, about 0.33%.

This astronomy paper discusses Earth’s equatorial radius as a measured quantity in calculations, reflecting that Earth’s radius is treated as an estimated geophysical parameter rather than a single perfect-sphere value.

The article states: "Earth is not a perfect sphere. Its shape is an oblate spheroid. This just means that it flattens at the poles and widens out at the equator." It notes that geographers model Earth's shape as an ellipsoid, and gives radii values: the equatorial radius is about 6,378 km while the polar radius is about 6,357 km, so someone at mean sea level at the equator is about 21.4 km farther from Earth's center than someone at the poles.

The Earth is by no means a perfect sphere. If you are standing at either the North or South Pole, you are some 21 km nearer to the center of the planet than if you were near the Equator. The reason for this is that the rotation of the planet exerts a centrifugal force that makes the Earth more of an oblate ellipsoid.

Geodetic reference systems such as WGS 84 model Earth as an oblate spheroid, not a perfect sphere. Typical values used in these systems are an equatorial (semi-major) axis of about 6,378.137 km and a polar (semi-minor) axis of about 6,356.752 km, corresponding to a flattening of approximately 1/298.25. These parameters encode the measured equatorial bulge and polar flattening of Earth’s figure.

A highly upvoted, expert-style answer in r/askscience explains: “**Yes, the Earth isn’t a perfect sphere; it’s actually an oblate ellipsoid.** … The equatorial diameter is slightly larger than the polar diameter. … If you need figures, **the Earth’s average equatorial diameter is 12,756 km and the polar diameter is 12,713 km. The difference is less than 1%,** so the planet appears almost spherical to the eye.” It also notes that the maximum deviation of the geoid from the reference ellipsoid is roughly ±100 m.

Approximating Earth as an oblate ellipsoid, the radius ranges from a maximum equatorial radius of about 6,378 km to a minimum polar radius of nearly 6,357 km. The page also lists the equatorial radius as 6,378.1370 km and the polar radius as 6,356.7523 km, showing that Earth is wider at the equator than at the poles.

A highly upvoted AskScience response explains that "Earth is said to be an oblate spheroid" because rotation pushes the equator outwards with centrifugal force. It states that "the earth's diameter across the equator is only 0.3% more than the distance between the poles," so while Earth is still basically spherical, it is measurably flattened, not a perfect sphere.

In this educational video the narrator explains: "The Earth is not a perfect sphere. It's an oblate spheroid, slightly flattened at the poles and slightly bulging at the equator." The video gives numerical values: an equatorial diameter of about 12,756 km and a polar diameter of about 12,714 km, stating that the difference is around 42 km and corresponds to an oblateness of about 0.3%.

TIL there is a sea bulge at the equator of the Earth. Sea level at the equator is 21.36 km (13.272 miles) higher than sea level at the poles, in large part because of Earth’s equatorial bulge. Using the flattening factor for the WGS-84 ellipsoid, the biggest difference between geodetic and geocentric latitude is about 0.2 degrees, illustrating that Earth’s shape deviates slightly from a perfect sphere.

Earth bulges at the equator due to its rotation. As Earth spins on its axis, centrifugal effects make the equator’s radius slightly larger than the radius to the poles. The bulge at the equator is a few miles compared to the polar radius, illustrating that Earth is not a mathematically perfect sphere even though the deviation is tiny relative to the planet’s overall size.

A post discussing Earth's figure states: "Earth is an oblate spheroid, This means it is spherical in shape, but not perfectly round. It is slightly bulged at the equator and is flattened ... Basically, it’s not a perfect sphere." The post cites that Earth's equatorial diameter is about 7,915.5 miles and that the equatorial bulge is around 27 miles larger than the north–south polar diameter.

The shape of Earth is not a perfect sphere, but an oblate spheroid — meaning it is slightly flattened at the poles and bulged at the equator. The rotation creates a centrifugal effect that pushes outward more strongly at the equator than at the poles, causing the equatorial region to bulge slightly. As a result, Earth’s equatorial diameter is about 43 kilometers (27 miles) larger than its polar diameter.

In this short explainer, the creator says that Earth's shape is technically called an "oblate spheroid" and describes it as a "squished sphere." She explains that because Earth is spinning, it bulges at the equator, so it is not a perfectly round sphere but slightly flattened.

The Earth's radius at the equator is 6,378 km. Earth's polar radius is 6,356 km, which is about 22 km less than the radius at the equator.

The Earth's equatorial radius is 6,378.14 kilometers, but its polar radius is 6,356.75 kilometers. The post states that this difference is due to equatorial bulge and polar flattening.