Astronomical Unit Converter
Convert a distance between astronomical units, metric units, light-years, parsecs, solar radii, and miles using exact or widely accepted conversion constants.
Distance to convert
Converted distance
Conversion table
| Quantity | Symbol | Converted value | Factor in meters |
|---|---|---|---|
| Astronomical units | au | 1 | 149,597,870,700 |
How to use this astronomical unit calculator
What this calculator does. This converter expresses one physical distance in seven common astronomy and length units. It is useful for translating Solar System distances into kilometers or miles, comparing interplanetary and interstellar scales, checking classroom work, and preparing consistent figures for reports. It performs unit conversion only: it does not predict an orbit, account for a planet's changing position, or calculate travel time for a spacecraft. The astronomical unit is treated as the exact length adopted by the International Astronomical Union: 149,597,870,700 meters. The IAU 2012 resolution defining the astronomical unit provides the formal basis for that constant.
When to use it. Use the calculator when you want to convert a planet-to-Sun distance from au to kilometers, translate a catalog distance from parsecs to light-years, compare a stellar radius scale with an orbital distance, or verify that values copied between metric and U.S. customary units remain consistent.
How to calculate. The calculator opens with a ready-to-use demonstration of 1 astronomical unit, so the results and Excel workbook are available immediately. (1) Replace the number in Distance value. (2) Choose the matching Source unit. (3) Read the live cards and the complete conversion table. (4) Select Download Excel to create a current-state workbook with inputs, outputs, constants, and checks. Reset clears the demonstration value and results; the download button then remains unavailable until a complete valid value is entered again.
Input guide. Distance value is required and accepts a non-negative decimal, including scientific notation such as 1.5e8. Use a period for the decimal separator. A realistic example is 5.2 for Jupiter's approximate mean orbital distance in au. Larger values increase every converted output proportionally. Negative values, commas used as decimal separators, mixed text, and non-finite numbers are rejected. Source unit is required and tells the converter how to interpret the number. Available choices are astronomical units, meters, kilometers, light-years, parsecs, solar radii, and miles. Changing this choice does not merely relabel the input: it converts the entered quantity through the canonical meter value.
Output guide. Astronomical units, Meters, Kilometers, Light-years, Parsecs, Solar radii, and Miles are exact identities within the constants and displayed precision used here. Zero means zero length; very large or very small values may switch to scientific notation for readability. Light travel time estimates how long light in vacuum takes to cross the distance, using the exact SI speed of light. The table repeats each quantity, its symbol, the converted value, and the unit's meter factor, so it is also a transparent formula audit rather than a separate calculation.
Worked example. With the startup value of 1 au, multiply by 149,597,870,700 meters per au. This gives exactly 149,597,870,700 m, or 149,597,870.7 km. Dividing by 1,000 converts meters to kilometers. Dividing by the light-year length gives approximately 0.0000158125 ly, while dividing by the parsec length gives approximately 0.00000484814 pc. At the exact speed of light, the same distance corresponds to about 499.0 seconds, displayed as 8 minutes 19.0 seconds. For background on exact SI constants, see the NIST fundamental physical constants reference.
How the conversion works
canonical meters = entered value × meters per selected source unit; each output = canonical meters ÷ meters per output unit
The calculation converts once into meters, then derives every displayed unit from that same canonical quantity. This avoids a chain of rounded conversions. One astronomical unit is exact by definition. One light-year is based on the distance light travels in a Julian year of 365.25 days, and one parsec follows from the geometry of one arcsecond of parallax. NASA's explanation of astronomical units and Solar System scale gives practical context for why au is convenient near the Sun, while the BIPM SI defining constants document explains the exact status of the speed of light used for the travel-time result.
Interpreting very large and very small results
Astronomical units are well suited to planetary systems, kilometers and miles are useful for engineering-scale comparisons, and light-years or parsecs are usually clearer for stellar distances. A tiny light-year result is not an error: one au is only about 1.58 × 10 – 5 light-years. Conversely, a distance of one parsec contains more than 206,000 au. The displayed precision is chosen to retain meaningful digits without forcing every card into a long unbroken number; the Excel workbook keeps the underlying numeric values.