Arcsecond (″)
A second of arc is one sixtieth of an arcminute, or 1/3600 of a degree. Astronomers measure star positions and parallax in arcseconds.
Symbol: ″ (ASCII: arcsec)
Quantity: plane angle
SI relation: 1 ″ = 0.000004848136811095 rad (exact)
Derivation: 1″ = (1/3600)° = π/648 000 rad.
Exact: yes, by definition
Typical uses
- Astronomy (parallax, star positions)
- Geodesy and GPS coordinates
- Precision optics
Convert seconds of arc to other units
| Conversion | 1 ″ equals | Reverse |
|---|---|---|
| second of arc to radian | 0.000004848136811 rad | radian to second of arc |
| second of arc to degree | 0.0002777777778 ° | degree to second of arc |
| second of arc to gradian | 0.0003086419753 gon | gradian to second of arc |
| second of arc to revolution | 7.716049383 × 10⁻⁷ rev | revolution to second of arc |
| second of arc to minute of arc | 0.01666666667 ′ | minute of arc to second of arc |
Open the Angle Converter to convert any value between all units.
Sources
- The International System of Units (SI), 9th edition (SI Brochure), Bureau International des Poids et Mesures , Table 4 (radian) and Table 8 (non-SI units accepted for use with the SI).
Last reviewed: . Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.
Cite this page
APA
Scientific Converters. (2026, October 15). Arcsecond (″). Retrieved October 25, 2026, from https://scientificconverters.com/units/arcsecond/
IEEE
Scientific Converters, "Arcsecond (″)," scientificconverters.com. Accessed: Oct. 25, 2026. [Online]. Available: https://scientificconverters.com/units/arcsecond/