Science & history · Our star
How big is the Sun?
The Sun is about 1.4 million kilometres across. Astronomers even agree on a standard value for its radius, so that measurements can be compared.
Today's distance and light time
Worked out in your browser for today's date.
Size and mass
NASA gives the Sun's radius as about 700,000 kilometres and its diameter as about 1.4 million. It would take 1.3 million Earths to fill its volume and more than 330,000 to match its mass.
In 2015 the International Astronomical Union adopted a nominal solar radius of 695,700 kilometres. It is a conversion constant, a fixed yardstick for writing other stars' sizes in "solar radii", rather than a claim that the Sun's edge is sharp to the kilometre: the Sun is gas all the way through.
How big it looks
Seen from Earth the Sun is about half a degree across, and that size changes slightly through the year because our distance changes: Earth is closest in early January. The page computes today's apparent size from today's distance (how).
Sources
- NASA Sun: Facts (opens in a new tab) for age, size, distance, temperatures, layers, rotation, cycle, type, future · checked 2 October 2026
- International Astronomical Union IAU 2015 Resolution B3: nominal solar and planetary conversion constants (Mamajek et al.) (opens in a new tab) for nominal radius 695,700 km, irradiance 1361 W/m², luminosity 3.828×10²⁶ W, effective temperature 5772 K · checked 2 October 2026
- NASA Space Place What Causes the Seasons? (opens in a new tab) for tilt, not distance; perihelion in January · checked 2 October 2026
- Cool Moon Facts How the Sun pages calculate for the engine, its definitions, its independent checks and its limits