The ten largest known exoplanets with confirmed radii, from ultra-puffy gas giants larger than 1.5 Jupiter radii down to the edge of the giant planet category.
Quick answer: 1. ROXs 42 Bb, 2. WASP-17b, 3. HAT-P-67b, 4. WASP-79b, 5. XO-6b, 6. HD 100546 b, 7. KELT-11b, 8. WASP-107b, 9. KELT-9b, 10. TrES-4b.
These are the ten largest exoplanets by measured radius, drawn from NASA's Exoplanet Archive. Most are hot Jupiters or young directly-imaged planets whose atmospheres have been puffed up by internal heat or proximity to their star. Several are so large they blur the line between planet and brown dwarf. The list showcases extremes: ROXs 42 Bb, a young planet still glowing from formation heat, spans nearly three Jupiter radii. At the other end, the familiar Jupiter itself serves as a yardstick at 1.0 Jupiter radii. The boundary at roughly 1.5 Jupiter radii marks the point where electron degeneracy in massive gas giants stops them from getting much bigger — a sweet spot in planetary physics.
A young directly-imaged exoplanet orbiting a brown dwarf in the Ophiuchus star-forming region. Discovered in 2013, it is one of the largest-radius exoplanets known, at the upper boundary of the planetary regime.
The first exoplanet discovered to orbit in a retrograde (backwards) direction relative to its star. Its exceptionally low density — about one-sixth that of Jupiter — makes it one of the puffiest known planets.
One of the largest-radius exoplanets discovered by the HATNet survey, with an extremely low density of about 0.05 g/cm³. Its inflated radius is attributed to intense stellar heating.
An ultra-hot Jupiter orbiting a bright F-type star, notable for its extremely bloated atmosphere that gives it one of the largest confirmed radii.
An inflated hot Jupiter discovered by the XO telescope project, orbiting a hot, rapidly rotating star. Its large radius is consistent with a low-density gas giant.
A directly-imaged protoplanet still embedded in its system's circumstellar disk. Its large measured radius may include extended circumplanetary material and a dusty envelope.
One of the lowest-density exoplanets ever discovered, with a density comparable to styrofoam. Its orbit around a bright subgiant star makes it an excellent target for atmospheric characterization.
A warm Neptune-mass planet with a strikingly large radius, giving it one of the lowest densities of any known exoplanet. Its puffy atmosphere was a prime target for JWST transmission spectroscopy.
The hottest known exoplanet, with a dayside temperature exceeding 4,600 K — hotter than many stars. Its extreme heat inflates its atmosphere to a large radius. It orbits a B-type star in a polar configuration.
One of the first extremely low-density exoplanets discovered, orbiting its host star in just 3.5 days. Its puffy structure helped establish the class of inflated hot Jupiters.
| # | Name | Distance | Constellation | Discovery Year | Method | Mass |
|---|---|---|---|---|---|---|
| 1 | ROXs 42 Bb | 440 ly | Ophiuchus | 2013 | Direct imaging | 9.9 M_J |
| 2 | WASP-17b | 1,000 ly | Scorpius | 2009 | Transit | 0.49 M_J |
| 3 | HAT-P-67b | 1,087 ly | Hercules | 2017 | Transit | 0.34 M_J |
| 4 | WASP-79b | 780 ly | Eridanus | 2013 | Transit | 0.90 M_J |
| 5 | XO-6b | 759 ly | Camelopardalis | 2016 | Transit | 1.9 M_J |
| 6 | HD 100546 b | 337 ly | Musca | 2015 | Direct imaging | 8.5 M_J |
| 7 | KELT-11b | 323 ly | Crater | 2016 | Transit | 0.17 M_J |
| 8 | WASP-107b | 200 ly | Virgo | 2017 | Transit | 0.12 M_J |
| 9 | KELT-9b | 670 ly | Cygnus | 2017 | Transit | 2.88 M_J |
| 10 | TrES-4b | 1,600 ly | Hercules | 2007 | Transit | 0.92 M_J |
Exoplanets are ranked by measured radius in Jupiter radii (R_J), where one Jupiter radius equals 69,911 km. Only confirmed exoplanets with published radius measurements in NASA's Exoplanet Archive (NexSci) as of July 2026 are included. Candidate or unconfirmed Kepler Objects of Interest (KOIs) are excluded. Radii from transit depth measurements are preferred; where only estimated radii from direct imaging or mass-radius models exist, the source uncertainty is noted. Rank 1 is the largest radius.
ROXs 42 Bb is among the largest confirmed exoplanets by radius at 2.86 Jupiter radii. Some exoplanet candidates like K2-3d and Kepler-447b have been reported with even larger radii, but their planetary status or radius precision remains under review.
Beyond roughly 1.5 Jupiter radii, electron degeneracy pressure in the planet's interior limits further expansion. Additional mass above about 13 Jupiter masses triggers deuterium fusion, crossing the threshold into brown dwarf territory. The puffiest planets achieve large radii through low density, not high mass.
The IAU working definition sets the boundary at about 13 Jupiter masses — above this threshold deuterium fusion can ignite in the core. Objects above ~75 Jupiter masses can fuse hydrogen and are classified as stars. Radius alone is not a reliable mass indicator, as low-mass puffy planets can be larger than more massive ones.
The most precise way is the transit method: when a planet passes in front of its star, the dimming of starlight reveals the planet's size relative to the star. Given the star's known radius, the planet's absolute radius can be calculated. Direct imaging gives a fainter measurement that depends on the planet's brightness model.