Parsecs (pc)
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Equivalent distance
Accurate conversion between kilometres (km) and parsecs (pc) for astronomy and astrophysics
Convert kilometres to parsecs instantly with precise calculations for 2026. Includes reverse parsecs to kilometres conversion, light-years, astronomical units, metres, megaparsecs, kiloparsecs, full formula reference, and astronomical distance reference tables.
Professional astronomical distance conversion for astronomers, astrophysicists, students, and space science enthusiasts
Convert kilometres to parsecs using the exact IAU-defined conversion factor: 1 parsec = 30,856,775,814.9 km (approximately 3.0857 × 10¹³ km), so 1 km = 3.24078 × 10⁻¹⁴ parsecs. This factor is derived from the IAU 2012 definition of the astronomical unit (AU = 149,597,870.7 km exactly) and the geometric definition of the parsec as the distance at which 1 AU subtends 1 arcsecond of angle. Our tool outputs parsecs, kiloparsecs, megaparsecs, light-years, astronomical units, and metres simultaneously.
Switch seamlessly between km → parsecs and parsecs → km conversion modes. Whether you are converting spacecraft trajectory distances from km to parsecs for stellar context, converting catalogue distances from parsecs to km, calculating the distance to nearby stars, comparing galactic distances, or studying cosmological structures expressed in megaparsecs, both directions are handled instantly from a single input with scientific notation output for very large or very small values.
Essential for astronomy students converting between metric distances and parsecs, astrophysicists working with stellar parallax measurements, researchers converting Hipparcos or Gaia star catalogue distances, educators teaching cosmic scale, space enthusiasts exploring interstellar distances, and anyone working with astronomical databases that express distances in parsecs or kiloparsecs in 2026 publications and data sets.
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A parsec (pc) is the fundamental unit of distance in professional astronomy. The name is a portmanteau of parallax and arcsecond: one parsec is the distance at which one astronomical unit (AU — the Earth–Sun distance) subtends an angle of exactly one arcsecond (1/3,600 of a degree) as seen from Earth. This geometrical definition means that a star at a distance of 1 parsec would show a parallax shift of 1 arcsecond as Earth moves around the Sun. Under the IAU 2015 nominal solar and planetary values, 1 parsec = 648,000 ÷ π astronomical units ≈ 3.08568 × 10¹³ km ≈ 3.26156 light-years. The parsec is preferred in professional astronomy because stellar parallax measurements directly yield distances in parsecs — a star with a parallax of p arcseconds is simply at a distance of 1/p parsecs.
The kilometre (km), by contrast, is the standard terrestrial distance unit — used for Earth-surface geography, spacecraft distances within the solar system, and engineering contexts. It is a practical unit for distances up to about 10 billion km (roughly 67 AU — just beyond the heliopause), but becomes unwieldy for stellar and galactic distances. The distance to Proxima Centauri, the nearest star, is about 40,000,000,000,000 km — a number so large it is almost meaningless without scientific notation, compared to the far cleaner expression of 1.30 parsecs. This is why astronomers universally use parsecs, kiloparsecs (kpc), megaparsecs (Mpc), and gigaparsecs (Gpc) for stellar, galactic, and cosmological distances. For related distance conversions in everyday and engineering contexts, see our kilometres to astronomical units converter.
1 pc = 3.08568 × 10¹³ km = 3.26156 ly = 206,265 AU | IAU 2015 nominal values
| Kilometres (km) | Parsecs (pc) | Light-Years (ly) | AU | Context / Object |
|---|---|---|---|---|
| 1 km | 3.2408 × 10⁻¹⁴ pc | 1.0570 × 10⁻¹³ ly | 6.685 × 10⁻⁹ AU | Short terrestrial distance |
| 1,000 km | 3.2408 × 10⁻¹¹ pc | 1.0570 × 10⁻¹⁰ ly | 6.685 × 10⁻⁶ AU | Earth's diameter (~12,742 km) |
| 384,400 km | 1.246 × 10⁻⁸ pc | 4.061 × 10⁻⁸ ly | 0.00257 AU | Earth–Moon distance |
| 149,597,870.7 km | 4.848 × 10⁻⁶ pc | 1.581 × 10⁻⁵ ly | 1.000 AU | 1 Astronomical Unit (Earth–Sun) |
| 778,500,000 km | 2.524 × 10⁻⁵ pc | 8.229 × 10⁻⁵ ly | 5.204 AU | Jupiter's orbital radius |
| 5,906,380,000 km | 1.914 × 10⁻⁴ pc | 6.243 × 10⁻⁴ ly | 39.48 AU | Pluto's average distance |
| 9,460,730,472,581 km | 0.30660 pc | 1.000 ly | 63,241 AU | 1 Light-Year |
| 4.013 × 10¹³ km | 1.300 pc | 4.243 ly | 268,269 AU | Proxima Centauri (nearest star) |
| 8.175 × 10¹³ km | 2.649 pc | 8.611 ly | 546,479 AU | Sirius (brightest star) |
| 3.086 × 10¹³ km | 1.000 pc | 3.262 ly | 206,265 AU | 1 Parsec (definition) |
| 3.086 × 10¹⁶ km | 1,000 pc = 1 kpc | 3,262 ly | 2.063 × 10⁸ AU | 1 Kiloparsec |
| 2.362 × 10¹⁷ km | ~8,500 pc | ~27,700 ly | 1.58 × 10⁹ AU | Distance to Galactic Centre |
| 3.086 × 10¹⁹ km | 1,000,000 pc = 1 Mpc | 3.262 × 10⁶ ly | 2.063 × 10¹¹ AU | 1 Megaparsec |
| 2.374 × 10¹⁹ km | ~770,000 pc | ~2.537 Mly | 1.587 × 10¹¹ AU | Andromeda Galaxy (M31) |
| 3.086 × 10²² km | 1 Gpc | 3.262 × 10⁹ ly | 2.063 × 10¹⁴ AU | 1 Gigaparsec |
The parsec is directly tied to the parallax method of measuring stellar distances — the oldest and most reliable astronomical distance measurement technique. A star with a parallax angle of p arcseconds is exactly 1/p parsecs away, making parsecs a natural output unit. This eliminates conversion steps when processing astrometric data from missions like ESA's Gaia, which has measured parallaxes — and therefore direct distances in parsecs — for over 1.5 billion stars in the Milky Way as of 2026.
The light-year is popular in public science communication because it links to the familiar concept of the speed of light. However, professional astronomers almost universally use parsecs in research papers, catalogues, and textbooks because parsecs arise naturally from parallax measurements and the IAU coordinate systems. 1 parsec = 3.26156 light-years exactly. When reading popular science articles in light-years and research papers in parsecs, knowing this conversion factor is essential to reconcile the two sources.
Parsec prefixes scale with cosmic structures: kiloparsecs (kpc) describe distances within the Milky Way (diameter ~30 kpc); megaparsecs (Mpc) describe intergalactic distances and galaxy cluster separations (Andromeda is ~0.77 Mpc away); gigaparsecs (Gpc) describe cosmological-scale distances (the observable universe radius is ~14.3 Gpc). The Hubble constant, describing the universe's expansion rate, is expressed in km/s/Mpc — directly combining both km and Mpc in a single unit.
1 parsec = 3.08568 × 10¹³ km = 3.26156 light-years = 206,265 AU = 3.08568 × 10¹⁶ metres
Mental shortcut: To convert km to parsecs, divide by 3.086 × 10¹³. To convert parsecs to km, multiply by 3.086 × 10¹³. For light-years to parsecs: divide light-years by 3.26156. For a rough check: the nearest star (Proxima Centauri) is about 1.3 parsecs or 4.24 light-years away.
Converting kilometres to parsecs requires dividing by the very large IAU-defined constant of 3.08568 × 10¹³. Follow these steps:
Moon: 384,400 km = 1.246 × 10⁻⁸ pc | Sun (1 AU): 149,597,871 km = 4.848 × 10⁻⁶ pc | Proxima Centauri: ~4.01 × 10¹³ km = 1.30 pc | Sirius: ~8.14 × 10¹³ km = 2.64 pc | Galactic Centre: ~2.6 × 10¹⁷ km = 8,500 pc | Large Magellanic Cloud: ~1.55 × 10¹⁸ km = 50,000 pc | Andromeda Galaxy: ~2.37 × 10¹⁹ km = 0.77 Mpc
The most frequent error is confusing parsecs with light-years — they are different units (1 pc = 3.26156 ly). Many popular science sources use light-years while professional astronomy uses parsecs; always identify which unit a source is using before converting. Another common mistake is confusing the parsec definition with the light-travel time definition of the light-year — a parsec is a geometric unit based on parallax angle, not a time-based unit. Additionally, when working with very large distances (galactic and cosmological), always use kiloparsecs (kpc), megaparsecs (Mpc), or gigaparsecs (Gpc) rather than raw parsecs, as the numbers become more manageable and less prone to power-of-ten errors.
In stellar astrometry and catalogue work, the ESA Gaia mission publishes stellar parallaxes in milliarcseconds (mas), from which distances are directly derived in parsecs as d = 1/p. Converting these parsec distances back to kilometres or light-years for public outreach, educational materials, or comparison with solar system distances requires precise km-to-parsec conversion. In galactic dynamics and structure, models of the Milky Way express spiral arm separations, galactic bar lengths, and disc thickness in kiloparsecs — but spacecraft mission designers planning hypothetical interstellar probes must work in km or AU. Converting between the two systems is routine in interdisciplinary space science work. For related cosmic distance conversions, see our kilometres to astronomical units converter.
In cosmology and extragalactic astronomy, the Hubble constant (approximately 67–73 km/s/Mpc in 2026) directly combines km and Mpc in one expression — making the km-to-parsec conversion fundamental to understanding the universe's expansion rate and the distance–redshift relationship. In education and public science communication, teachers and science writers regularly need to convert between the parsec distances published in professional literature and the more intuitive light-year or km values that audiences can relate to. Understanding that Proxima Centauri at 1.30 pc is the same as 40.2 trillion km helps communicate the true scale of interstellar space. For speed conversions relevant to rocket propulsion and spacecraft trajectories, see our km/h to m/s converter.
The International Astronomical Union (IAU) provides the official definition of the parsec and astronomical unit used in all professional astronomy worldwide. The 2012 IAU Resolution B2 defined 1 AU = 149,597,870,700 metres exactly, establishing the exact km-to-parsec conversion factor used in this tool for 2026.
Visit IAU →ESA's Gaia astrometry mission has measured precise parallaxes — and therefore direct distances in parsecs — for over 1.5 billion stars across the Milky Way. Gaia Data Release 3 (2022) and subsequent releases provide the most accurate stellar distance catalogue in history, with all distances expressed in parsecs and milliarcsecond parallaxes.
Visit ESA Gaia →Explore our full library of free unit conversion tools for distance, speed, power, energy, force, weight, area, flow rate, and time. All tools are updated for 2026 standards and fully optimised for mobile and desktop use with scientific notation support for astronomical-scale values.
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