Why it became famous
UY Scuti's estimated radius can be over a thousand times the Sun's radius, placing it in the public imagination as a record-breaking star.
Those estimates depend on distance, temperature, dust, and model choices.
Is it the biggest star?
It is one of the largest candidates, but not a guaranteed permanent number one. Other stars can appear larger depending on the measurement set used.
A scientifically honest page says it is among the largest known stars, not definitely the largest.
The useful scale comparison
If a star of this scale replaced the Sun, its outer layers could extend toward Jupiter's orbit. That is the intuition people search for, and it should be paired with uncertainty.