The universe is all of space and everything in it. Nobody knows how big it is, and it may be infinite. The size shown above, 1,600 yottameters (about 170 billion light-years), is not a measurement. A light-year is the distance light travels in one year.

Size

The part that can be measured is the observable universe, the region from which light has had time to reach Earth since the Big Bang. It is about 93 billion light-years across. The whole universe is probably much larger, but so far its size has only been limited, not measured.

One way to set a limit is to measure the shape of space. If space curved back on itself, like the surface of a ball, the universe would have a finite size. Measurements by the Planck satellite, combined with surveys of galaxies, show that space is flat to within about 0.2%.

A 2011 analysis combined measurements like these. It found, with 99% confidence, that the universe holds at least 251 times the volume of the observable universe. If space is exactly flat, or curves the other way, and has no unusual shape, the universe goes on forever.

Size comparisons

If the observable universe were shrunk to the size of a basketball, about 24 centimeters (9.4 inches) across, the whole universe would hold at least as much space as a ball 1.5 meters (5 feet) across.
By volume, the whole universe would hold at least 8 × 10⁶¹ planets the size of Earth, where 10⁶¹ is a 1 followed by 61 zeros.
A space that wraps around could in principle be smaller than the observable universe. A 2004 search ruled out, for a wide range of shapes, a universe smaller than 24 gigaparsecs (78 billion light-years) across. That is about 84% of the width of the observable universe.

Searching for a universe that wraps around

Space could be finite without curving, if it wraps around on itself. Some video games work this way: a ship that leaves one edge of the screen comes back on the opposite edge. In such a universe, light from the same region could reach Earth from more than one direction.

The cosmic microwave background, the faint glow left from the early universe, would then show matching circles of hot and cold spots in different parts of the sky. In 2004, a team searched maps from NASA's WMAP spacecraft for such circles. They found no matching circles with a radius larger than 25 degrees.

For a wide range of possible shapes, that rules out a universe smaller than 24 gigaparsecs across, where a gigaparsec is about 3.26 billion light-years. The search could not rule out larger wrap-around universes, or an infinite one.

Sources

Planck 2018 results. VI. Cosmological parameters. Planck Collaboration, Astronomy and Astrophysics, 2020.
Applications of Bayesian model averaging to the curvature and size of the Universe. Vardanyan et al., Monthly Notices of the Royal Astronomical Society, 2011.
Constraining the Topology of the Universe. Cornish et al., Physical Review Letters, 2004.
A Map of the Universe. Gott et al., The Astrophysical Journal, 2005.
Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the Universe. Davis and Lineweaver, Publications of the Astronomical Society of Australia, 2004.
Measuring the Universe. International Astronomical Union.
Planck reveals an almost perfect Universe. European Space Agency, 2013.
Earth Fact Sheet. NASA, 2024.
Official Basketball Rules 2026: Basketball Equipment. FIBA, 2026.

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