How big are the planets and stars?
Jupiter is 11 times the width of Earth. The Sun is 109 times Earth. The black hole at the centre of the Milky Way is 17 times the Sun — and then Betelgeuse is about 45 times that, which is the step almost nobody guesses. Saturn is smaller than Jupiter until you count its rings, and wider than the Sun if you count all of them.
Those are the answers. The rest of this page is how they were arrived at, and what to do about the ones the astronomers still disagree on.
Big enough that a single picture cannot hold them. Every other page on this site draws its subjects at one shared scale, because that is the honest way to compare areas that differ by a factor of forty. The bodies here differ by a factor of 1.7 billion. Drawn together at one scale, everything below the largest would be less than a pixel across, which is a picture of nothing.
So this page walks instead. Each step re-scales, so the body you just looked at shrinks away while the next one grows in, and the running multiplier tells you how far from the start you have travelled. Nothing is ever drawn too small to see, and nothing is drawn at a scale that flatters it.
Which is bigger, Betelgeuse or the black hole at the centre of the galaxy?
Betelgeuse, by roughly forty-five times — and almost nobody guesses that. Sagittarius A*, the Milky Way's central black hole, has an event horizon about 12 million km across its radius, which is around seventeen times the Sun. That sounds final until you put a red supergiant next to it. Betelgeuse is somewhere above 500 million km. The object everyone assumes is the biggest thing in the list sits second from the end.
Why does this page let me pick the size?
Because up here the measurements genuinely disagree, and picking one for you would be pretending otherwise. Published radii for Betelgeuse span a factor of 2.6, from around 500 solar radii to about 1,300, depending on whether you fit the 420-day pulsation or the 2,200-day one. UY Scuti spent years cited as the largest star known at 1,700 solar radii and was later revised to 755 — smaller than Betelgeuse. That is not a correction to a decimal place; it is an object leaving the top of the list entirely.
Every body with more than one published figure carries all of them, with their sources, and you choose which one gets drawn. The table at the bottom of this page lists every value whether or not you ever touch the control.
Is Saturn bigger than Jupiter?
It depends entirely on whether you count the rings, which is the clearest example on the site of a question with more than one true answer. Saturn's body is about 58,000 km in radius, comfortably smaller than Jupiter's 70,000. Count out to the outer edge of the main rings and it reaches roughly 137,000 km, which is nearly twice Jupiter. Count the faint E ring, which reaches out towards Titan's orbit, and Saturn is wider than the Sun.
All three are correct. The picker makes you say which Saturn you meant, and the journey reorders itself around the answer — with the main rings Saturn overtakes Jupiter, and with the E ring it moves past the Sun.
Where do these numbers come from?
Solar-system radii are the NASA Planetary Fact Sheet volumetric means, the same source the rest of the site's non-geographic figures use. Stellar radii are quoted in solar radii against the IAU nominal value of 695,700 km. The two black holes are given by mass, with the Schwarzschild radius derived from it — and the derivation is re-run by this project's test suite on every build, so the file and the arithmetic cannot drift apart.
Every figure on this page
| Body | Radius (km) | Published value | Source |
|---|---|---|---|
| M87* | 19,201,065,000 | from its mass, 6.5 billion suns | Event Horizon Telescope, 2019 |
| 18,210,000,000 | from the published 5.9e-4 pc | same result within 5% | |
| Stephenson 2-18 | 1,495,755,000 | 2150 R☉ | disputed - larger than current theory allows |
| WOH G64 | 1,071,378,000 | 1540 R☉ | Large Magellanic Cloud |
| VY Canis Majoris | 987,894,000 | 1420 R☉ | commonly cited |
| Betelgeuse | 347,850,000 | 500 R☉ | low end of the published range |
| 542,646,000 | 780 R☉ | Joyce et al. 2020, seismological | |
| 904,410,000 | 1300 R☉ | 2023 pulsation-period models | |
| UY Scuti | 1,182,690,000 | 1700 R☉ | the older figure, long cited as the largest star |
| 525,253,500 | 755 R☉ | revised; smaller than Betelgeuse | |
| Sagittarius A* | 12,000,000 | event horizon | NASA JPL / Britannica |
| 12,702,243 | from its mass, 4.3 million suns | 2GM/c^2 | |
| Sun | 695,700 | the published figure | IAU nominal / NASA volumetric mean |
| Jupiter | 69,911 | the published figure | NASA Planetary Fact Sheet |
| Saturn | 58,232 | body only | NASA Planetary Fact Sheet |
| 136,770 | with main rings | A ring outer edge | |
| 1,221,870 | with the E ring | diffuse, out to about Titan's orbit | |
| Uranus | 25,362 | the published figure | NASA Planetary Fact Sheet |
| Neptune | 24,622 | the published figure | NASA Planetary Fact Sheet |
| Earth | 6,371 | the published figure | NASA Planetary Fact Sheet |
| Venus | 6,052 | the published figure | NASA Planetary Fact Sheet |
| Mars | 3,390 | the published figure | NASA Planetary Fact Sheet |
| Ganymede | 2,634 | the published figure | NASA Planetary Fact Sheet |
| Titan | 2,575 | the published figure | NASA Planetary Fact Sheet |
| Mercury | 2,440 | the published figure | NASA Planetary Fact Sheet |
| Callisto | 2,410 | the published figure | NASA Planetary Fact Sheet |
| Io | 1,822 | the published figure | NASA Planetary Fact Sheet |
| Moon | 1,737 | the published figure | NASA Planetary Fact Sheet |
| Europa | 1,561 | the published figure | NASA Planetary Fact Sheet |
| Pluto | 1,188 | the published figure | NASA Planetary Fact Sheet |
| Eris | 1,163 | the published figure | NASA Planetary Fact Sheet |
| Makemake | 715 | the published figure | NASA Planetary Fact Sheet |
| Ceres | 470 | the published figure | NASA Planetary Fact Sheet |
| Vesta | 263 | the published figure | NASA Planetary Fact Sheet |
| Enceladus | 252 | the published figure | NASA Planetary Fact Sheet |
| Mimas | 198 | the published figure | NASA Planetary Fact Sheet |
| Phobos | 11 | the published figure | NASA Planetary Fact Sheet |
How to use it
Scroll, drag or use the arrow keys to walk up the chain. Each step re-scales, so the body you just looked at shrinks away while the next one grows in, and the readout gives you both the step and the running multiple from where you started. Click any name on the size line to jump straight to it. Where a body has more than one published radius, the picker beside the readout chooses which is drawn, and the journey reorders itself around your answer. Nothing to install, and it works offline.
Solar-system radii are NASA Planetary Fact Sheet volumetric means. Stellar radii are quoted in solar radii against the IAU nominal value of 695,700 km. The two black holes are given by mass, with the Schwarzschild radius derived from it and re-derived by this project's test suite on every build, so the published figure and the arithmetic cannot drift apart. Where the literature disagrees the disagreement is shipped rather than resolved.