The Biggest Star in the Universe: How the Largest Known Stars Compare to the Sun
Stars · Size comparison · Updated 2026-07-22
The largest known star is most likely WOH G64, a red supergiant in the Large Magellanic Cloud measured at 1,540 ± 77 solar radii - roughly 2.14 billion km across, or about 1,540 times the Sun's radius. A handful of others sit close enough to contest the title: VX Sagittarii, VY Canis Majoris and AH Scorpii all land near 1,400 to 1,550 solar radii once you allow for their error bars.
The figure you will see quoted most often elsewhere - UY Scuti at 1,708 solar radii - comes from a single 2013 measurement that assumed the star sat 2.9 kiloparsecs away. Gaia parallax data moved it much closer, and the current published value is about 909 solar radii. This guide gives the ranked list with the uncertainty on each entry, the source behind every number, and the arithmetic you need to sanity-check any size claim you meet.
Largest known stars compared to the Sun
| Star | Type | Radius (solar radii) | Diameter (km) | Distance (light years) | Constellation | Would reach |
|---|---|---|---|---|---|---|
| Stephenson 2 DFK 1 (St2-18) [1] | Red supergiant / possible red hypergiant | ~2,150, heavily disputed | ~3.0 billion | ~18,900, uncertainty over 50% | Scutum | About 10.0 AU - past Saturn's orbit, if the distance holds |
| WOH G64 [2] | Red supergiant / red hypergiant | 1,540 ± 77 | ~2.14 billion | ~163,000 (Large Magellanic Cloud) | Dorado | About 7.2 AU - between Jupiter and Saturn |
| VX Sagittarii [3] | Pulsating red supergiant / hypergiant | 1,456 ± 108 quiescent to 1,556 ± 110 active | 2.03 - 2.17 billion | 5,100 ± 300 | Sagittarius | 6.8 - 7.2 AU - past Jupiter |
| VY Canis Majoris [4] | Red hypergiant | 1,420 ± 120 | ~1.98 billion | 3,820 (+260 / -230) | Canis Major | About 6.6 AU - past Jupiter |
| AH Scorpii [5] | Red supergiant / hypergiant | 1,411 ± 124 | ~1.96 billion | 7,400 ± 620 | Scorpius | About 6.6 AU - past Jupiter |
| RW Cephei [6] | Hypergiant, K-type (called yellow or red) | 1,100 ± 40 | ~1.53 billion | 12,790 (+550 / -510) | Cepheus | About 5.1 AU - stops just short of Jupiter's orbit |
| UY Scuti [7] | Red supergiant / hypergiant | 909 current; 1,708 ± 192 in the older estimate | 1.26 billion current (2.38 billion under the old figure) | ~5,900 | Scutum | About 4.2 AU - four fifths of the way to Jupiter |
| Mu Cephei (Garnet Star) [8] | Red supergiant / hypergiant | 762 in the latest work; older studies to ~1,420 | ~1.06 billion | 1,370 (+190 / -140) | Cepheus | About 3.5 AU - just past the main asteroid belt |
| Betelgeuse [9] | Red supergiant | ~640 - 764 (+116 / -62) | 0.89 - 1.06 billion | ~400 - 600, commonly cited as 548 | Orion | 3.0 - 3.6 AU - past Mars, into the asteroid belt |
| The Sun (reference) | G2V main sequence | 1 | 1.392 million | 8.3 light minutes | - | Its own surface, 0.0047 AU |
- Sources. [1] Fok et al. 2012, from an assumed 3,200 K effective temperature; cluster membership and therefore distance are contested. [2] Levesque et al. 2009. [3] Jadlovsky et al. 2023, quiescent and active phase values; a still larger radius near 1,800 solar radii has been published for its 2019 maximum. [4] Wittkowski et al. 2012, Rosseland radius from near-infrared interferometry. [5] Arroyo-Torres et al. 2013, with a later re-measurement of the angular diameter. [6] Anugu et al. 2024, measured after the 2022 dimming event. [7] Healy et al. 2023 using Gaia DR3; the 1,708 ± 192 figure is from 2013 VLT/AMBER interferometry. [8] The 762 figure is the value carried in current compilations from recent spectroscopic work; the distance remains poorly constrained. [9] Multiple, including Mittag et al. 2020 and Joyce et al. 2020.
- Every radius above is a derived quantity, not a ruler reading. Most come from the Stefan-Boltzmann law applied to an estimated luminosity and effective temperature, or from an angular diameter measured by interferometry and then multiplied by an assumed distance. Both routes inherit the error on the distance.
How to check any size claim yourself
Three constants do all the work. The solar radius is 695,700 km, one astronomical unit is 149,597,870 km, and dividing the second by the first gives 215 solar radii per AU. So any radius in solar radii converts straight into a Solar System distance: divide by 215 for AU, multiply by 695,700 for km, and double it for diameter. Jupiter's orbit sits at 5.20 AU, which is 1,119 solar radii; Saturn's is 9.58 AU, or 2,061 solar radii. That is why anything above roughly 1,120 solar radii is described as swallowing Jupiter's orbit.
Now the worked example that explains the whole UY Scuti mess. Interferometry measures an angle, not a size, so the radius you publish scales linearly with the distance you assume. The 2013 result took an angular diameter and a distance of 2.9 kpc (about 9,500 light years) and got 1,708 solar radii. Gaia parallaxes put UY Scuti closer, near 1.8 kpc. Scale the old number by the new distance - 1,708 × (1.8 / 2.9) = about 1,060 solar radii - and most of the shrinkage falls out of the distance revision alone. Healy et al. (2023) land at 909 once a 3,550 K effective temperature is folded in. The star did not shrink by 800 Suns. Our measurement of how far away it is changed.
Which planetary orbit would each star swallow?
- Betelgeuse and Mu Cephei would engulf Mercury, Venus, Earth and Mars, with their surfaces sitting inside or just beyond the asteroid belt.
- UY Scuti at its current 909 solar radii stops around 4.2 AU, roughly four fifths of the way out to Jupiter. Under the old 1,708 figure it would have reached almost 8 AU.
- RW Cephei is the near miss at about 5.1 AU: Jupiter's orbit is 5.20 AU, so it stops just short of the largest planet's path.
- VY Canis Majoris, AH Scorpii, VX Sagittarii and WOH G64 all clear Jupiter's orbit and sit in the gap between Jupiter and Saturn.
- Only Stephenson 2 DFK 1, if its disputed 2,150 solar radii and 18,900 light year distance survive, would reach past Saturn's orbit - and that is exactly the entry the professionals trust least.
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Why the answer keeps changing
There is no governing body that certifies the largest star, and no equivalent of the IAU planet vote to settle it. What exists is a moving set of published measurements, and the ranking reshuffles every time a parallax, a temperature scale or an interferometric baseline improves. The honest answer to "what is the biggest star in the universe" is WOH G64 among known stars, by a margin smaller than the error bars, and with the caveat that we have surveyed a vanishing fraction of the galaxies out there. If you want to keep pace with the revisions rather than the listicles, StarQuest's Recent Discoveries collection pulls fresh findings from the scientific frontier, and the Galaxies and Supernovas categories cover where these stars come from and how they end. See also how black holes scale and the planets ranked by size for the other end of the ruler.
Frequently asked questions
What is the biggest star in the universe?
The largest star currently known is WOH G64 in the Large Magellanic Cloud, measured at 1,540 ± 77 solar radii by Levesque et al. (2009). VX Sagittarii, VY Canis Majoris and AH Scorpii are close enough that their error bars overlap with it, so the title is genuinely contested. Stephenson 2 DFK 1 has a larger published figure of about 2,150 solar radii, but its distance is uncertain by more than 50%.
How big is UY Scuti compared to the Sun?
About 909 times the Sun's radius according to Healy et al. (2023) using Gaia DR3 data, which works out to roughly 1.26 billion km across. The widely repeated 1,708 solar radii figure comes from a 2013 measurement that assumed a much greater distance, and it has not held up.
Is UY Scuti still the largest star?
No. It held the popular title on the strength of one 2013 estimate, but revised Gaia parallax distances cut its radius by roughly half, and it now sits well outside the top ten. Most magazine listicles have not been updated.
How many Suns can fit inside the biggest star?
By volume, roughly 3.6 billion. Volume scales with the cube of radius, so a star of 1,540 solar radii holds 1,540 cubed, or about 3.65 billion times the Sun's volume - though its average density is a tiny fraction of the Sun's, so it holds only a few tens of solar masses of material.