What is the biggest known exoplanet?
The largest catalogued radii belong to young companions whose size is a model fit rather than a measurement, so this record is held to planets measured geometrically as they cross their star: the biggest of those is TOI-1408 b, at 2.23 times the radius of Jupiter. Everything about TOI-1408 b →
| # | World | Radius | Distance |
|---|---|---|---|
| ★ 1 | TOI-1408 b | 2.23× Jupiter's radius | 455 ly |
| 2 | HAT-P-67 b | 2.14× Jupiter's radius | 1,212 ly |
| 3 | TOI-3540 A b | 2.10× Jupiter's radius | distance unknown |
| 4 | XO-6 b | 2.07× Jupiter's radius | 768 ly |
| 5 | HAT-P-41 b | 2.05× Jupiter's radius | 1,136 ly |
| 6 | HIP 65 A b | 2.03× Jupiter's radius | 202 ly |
| 7 | Kepler-435 b | 1.99× Jupiter's radius | 4,627 ly |
| 8 | HAT-P-32 b | 1.98× Jupiter's radius | 943 ly |
| 9 | WASP-12 b | 1.96× Jupiter's radius | 1,393 ly |
| 10 | TOI-5811 B b | 1.96× Jupiter's radius | 555 ly |
| 11 | KELT-9 b | 1.94× Jupiter's radius | 667 ly |
| 12 | WASP-78 b | 1.93× Jupiter's radius | 2,460 ly |
| 13 | BD-14 3065 b | 1.93× Jupiter's radius | 1,922 ly |
| 14 | KELT-19 A b | 1.91× Jupiter's radius | 979 ly |
| 15 | TOI-1518 b | 1.88× Jupiter's radius | 737 ly |
| 16 | HAT-P-70 b | 1.87× Jupiter's radius | 1,079 ly |
| 17 | WASP-17 b | 1.87× Jupiter's radius | 1,324 ly |
| 18 | HATS-23 b | 1.86× Jupiter's radius | 2,084 ly |
| 19 | WASP-76 b | 1.85× Jupiter's radius | 634 ly |
| 20 | HAT-P-33 b | 1.85× Jupiter's radius | 1,292 ly |
| 21 | WASP-178 b | 1.81× Jupiter's radius | 1,395 ly |
| 22 | KELT-12 b | 1.78× Jupiter's radius | 1,200 ly |
| 23 | TOI-2193 A b | 1.77× Jupiter's radius | 1,099 ly |
| 24 | TOI-2669 b | 1.76× Jupiter's radius | 1,283 ly |
| 25 | Kepler-12 b | 1.75× Jupiter's radius | 2,875 ly |
Showing the top 25 of 1,620 that qualify.
A transiting planet's radius is measured, not inferred: the planet blocks a fixed fraction of its star's disc every orbit, and that fraction is a direct ratio of the two sizes. A directly imaged companion has no such geometry, so its radius comes from an evolutionary model that depends on an assumed age, and young objects come out enormous. Both kinds of number sit in the same catalog column, which is why the unfiltered radius ranking is misleading.
The second gate is physical. A gas giant swells past Jupiter's size only when its star pours enough heat into it to puff up the atmosphere, so this table is scoped to strongly irradiated worlds, above 1,000 K. A cool giant catalogued at three Jupiter radii is a fit that has gone wrong, not the biggest planet ever found. For scale, Jupiter is eleven times Earth's radius, and the worlds here are twice that again.
What is the biggest known exoplanet?
The largest catalogued radii belong to young companions whose size is a model fit rather than a measurement, so this record is held to planets measured geometrically as they cross their star: the biggest of those is TOI-1408 b, at 2.23 times the radius of Jupiter.
Why are the biggest planets not much bigger than Jupiter?
Because adding mass to a gas giant stops making it bigger. Past about Jupiter's mass the extra weight compresses the interior as fast as it adds material, so a planet ten times Jupiter's mass is roughly Jupiter's size. Only intense heating from a nearby star inflates one further, which is why every world near the top of this table orbits close in and runs hot.
How big is the biggest exoplanet compared to Jupiter?
TOI-1408 b measures 2.23× Jupiter's radius, which makes it roughly twice Jupiter's width and around a quarter the diameter of a small star.
Could a planet be as big as a star?
In width, almost. The most inflated hot Jupiters are close to the size of the smallest red dwarfs, which is a striking coincidence rather than a relationship: a star that size holds a hundred times more mass in the same volume, and it fuses hydrogen where a planet cannot.
Keep exploring: all records · the most massive planet · every hot Jupiter