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To convert solar radii to km: multiply by 696,340. To convert solar radii to AU: multiply by 0.00465.
1 R☉ = 6.9634 × 10⁸ m = 696,340 km ≈ 109 × Earth's radius ≈ 0.00465 AU.
For example, 1 Sun's Radius (R☉) = 6.963400e+23 Femtometer (fm).
| Sun's Radius (R☉) | Femtometer (fm) |
|---|---|
| 0.1 | 6.963400e+22 |
| 0.5 | 3.481700e+23 |
| 1 | 6.963400e+23 |
| 2 | 1.392680e+24 |
| 5 | 3.481700e+24 |
| 10 | 6.963400e+24 |
| 25 | 1.740850e+25 |
| 50 | 3.481700e+25 |
| 100 | 6.963400e+25 |
| 500 | 3.481700e+26 |
| 1000 | 6.963400e+26 |
The solar radius is the radius of the Sun, approximately 6.9634 × 10⁸ meters (about 696,340 km).
1 R☉ = 6.9634 × 10⁸ m = 696,340 km ≈ 109 × Earth's radius ≈ 0.00465 AU.
To convert solar radii to km: multiply by 696,340. To convert solar radii to AU: multiply by 0.00465.
Describing stellar sizes: Betelgeuse ≈ 700 R☉, Sirius ≈ 1.7 R☉, a white dwarf ≈ 0.01 R☉.
You could line up about 109 Earths across the Sun's diameter. The largest known star (UY Scuti) is about 1,700 R☉.
Confusing solar radius with solar diameter — the diameter is 2 R☉. Also, stellar catalogs list radius, not diameter.
The Sun's radius (109 × Earth) gives a sense of scale: you could fit over a million Earths inside the Sun by volume.
The femtometer is a unit of length equal to 10⁻¹⁵ meters, commonly used to measure the size of atomic nuclei.
1 fm = 10⁻¹⁵ m = 1,000 am = 10⁻⁶ nm. One meter equals 10¹⁵ femtometers.
To convert fm to meters: multiply by 10⁻¹⁵. To convert meters to fm: multiply by 10¹⁵.
Describing the size of protons (~0.87 fm radius) and nuclear diameters (1–15 fm depending on the element).
A proton's charge radius is approximately 0.87 fm. The diameter of a uranium-238 nucleus is about 15 fm.
Confusing femtometers with nanometers — a femtometer is one million times smaller than a nanometer.
Remember: atoms are ~0.1 nm, but nuclei are ~1–10 fm — nuclei are about 100,000 times smaller than the whole atom.



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