If placed in our solar system, the largest recorded star would swallow Saturn. It could hold nearly 10 billion Suns—a scale astrophysicists argue is physically impossible.
Because of this uncertainty, the crown for the "biggest known star" frequently changes hands. Measuring the exact boundaries of a red supergiant is notoriously difficult. These stars are shrouded in thick shells of dust and their outer envelopes constantly pulsate, making it hard to agree on where the star ends and space begins.
Currently, three major contenders define the debate:
The Former Champion: UY Scuti
For years, UY Scuti was the undisputed king of stars. It was estimated to have a radius 1,708 times that of the Sun, giving it roughly 5 billion times the solar volume. However, recent parallax measurements from the Gaia space observatory slashed this estimate in half. Better data showed the star was much closer to Earth than previously thought, dropping its estimated size to between 755 and 909 solar radii. It remains a behemoth, but it is no longer the record-holder.
The Pop Culture Record-Holder: Stephenson 2-18
Search for the largest star today, and you will likely find Stephenson 2-18. It holds the largest cited size estimate at roughly 2,150 solar radii, creating the impossible 10-billion-Sun scale. However, this measurement is highly disputed among astrophysicists. The 2,150-radii figure breaks the theoretical maximum limit of how big a red supergiant can physically get before it sheds its outer layers. Many astronomers believe the estimate relies on faulty assumptions about the star's distance and luminosity.
The Current Scientific Consensus: WOH G64
This is the star most astrophysicists point to today as the most scientifically defensible candidate. Located in the Large Magellanic Cloud, WOH G64 has a well-characterized estimate of about 1,540 solar radii, which translates to roughly 3.65 billion times the volume of the Sun. If WOH G64 replaced our Sun, its surface would swallow everything up to the orbit of Jupiter. The measurement holds up better to scrutiny than Stephenson 2-18, though it still comes with the inherent uncertainty of measuring a pulsating, dust-shrouded star in a neighboring galaxy.