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Astronomical Unit Calculator

Convert astronomical units, kilometers, miles, meters, and light-years using the official AU value of 149,597,870,700 meters.

Published

Converted distance
1 AU equals
149,597,870.7 km
Astronomical units (AU)
1 AU
Miles (mi)
92,955,807.273 mi
Light-years (ly)
0.0000158125 ly
Meters (m)
149,597,870,700 m

Uses the IAU fixed definition 1 AU = 149,597,870,700 meters.

Enter a Solar System distance to convert.

Results update as you type.

Astronomical Unit Calculator

Solar System distances can be awkward in ordinary length units. A planet may be hundreds of millions of kilometers from the Sun, a comet may swing from less than 1 AU to dozens of AU, and a spacecraft trajectory may need both mission-friendly kilometers and astronomy-friendly astronomical units. The Astronomical Unit Calculator converts among AU, kilometers, miles, meters, and light-years while using the official AU definition built into the converter.

The calculator accepts any supported starting unit. Keep the default settings to convert 1 AU to kilometers, or choose miles, meters, or light-years as the source or destination. The result panel also lists the same distance in every other supported unit so you can compare a Solar System number against a familiar road unit, an SI equation, or the beginning of interstellar scale.

Unit definition and history

An astronomical unit, abbreviated AU in this calculator, is exactly 149,597,870,700 meters. The International Astronomical Union adopted the fixed value so that an AU is a defined length rather than a value inferred from changing orbital models. Historically, the unit represented the Earth-Sun distance and helped astronomers compare planetary orbits before radar ranging and spacecraft tracking made direct measurements much more precise.

The modern definition is still close to Earth’s average distance from the Sun, which is why AU remains intuitive. Mercury’s orbital scale is less than 1 AU, Earth is near 1 AU, Mars is around 1.5 AU, Jupiter is a little over 5 AU, and Neptune is around 30 AU. Those numbers show the architecture of the Solar System far more clearly than repeatedly writing billions of meters.

Kilometers and meters are SI-based units. Miles are included because public astronomy articles, classroom material in the United States, and outreach pages often quote planetary distances in miles. Light-years are included as a bridge to stellar distances, although a light-year is much larger than an AU. For a dedicated stellar-scale page, use the Light Year Conversion. For ordinary units, use the length converter, and for road-scale comparisons use miles to kilometers.

Formula

The calculator first converts the input to meters:

meters=input value×meters per input unit\text{meters} = \text{input value} \times \text{meters per input unit}

For an AU input, the meter relationship is:

meters=AU×149,597,870,700\text{meters} = \text{AU} \times 149{,}597{,}870{,}700

The target value is then found by dividing by the target unit’s meter length:

target value=metersmeters per target unit\text{target value} = \frac{\text{meters}}{\text{meters per target unit}}

The factors used by the calculation are 1000 meters per kilometer, 1609.344 meters per mile, 1 meter per meter, 149,597,870,700 meters per AU, and 9,460,730,472,580,800 meters per light-year.

A worked conversion

Use the default conversion from 1 AU to kilometers. The calculator multiplies the input by the AU meter factor:

meters=1×149,597,870,700=149,597,870,700 m\text{meters} = 1 \times 149{,}597{,}870{,}700 = 149{,}597{,}870{,}700\ \text{m}

It then divides by 1000 meters per kilometer:

kilometers=149,597,870,7001000=149,597,870.7 km\text{kilometers} = \frac{149{,}597{,}870{,}700}{1000} = 149{,}597{,}870.7\ \text{km}

For miles, the same meter value is divided by 1609.344:

miles=149,597,870,7001609.344≈92,955,807.273 mi\text{miles} = \frac{149{,}597{,}870{,}700}{1609.344} \approx 92{,}955{,}807.273\ \text{mi}

For light-years, the same distance is divided by 9,460,730,472,580,800:

light-years≈0.0000158125 ly\text{light-years} \approx 0.0000158125\ \text{ly}

That tiny light-year result is expected. A light-year is a stellar-distance unit, while AU is meant for the Solar System.

Reference table

DistanceKilometersMilesMetersLight-years
0.387 AU57,894,375.961 km35,977,423.415 mi57,894,375,960.9 m0.000006118
1 AU149,597,870.7 km92,955,807.273 mi149,597,870,700 m0.0000158125
1.524 AU227,987,155.747 km141,664,650.282 mi227,987,155,746.8 m0.000024094
5.2 AU777,908,927.64 km483,370,197.82 mi777,908,927,640 m0.000082225
30 AU4,487,936,121 km2,788,674,218.18 mi4,487,936,121,000 m0.000474376

The planet-related rows are scale examples, not exact orbital ephemerides. Real planet-Sun distances vary continuously because orbits are elliptical. Use the calculator for unit conversion, and use an ephemeris or mission source when the date-specific distance matters.

Domains and interpretation

In astronomy education, AU keeps comparisons readable. Students can understand that Jupiter’s orbit is about five times Earth’s orbital scale without being distracted by many zeros. In observational astronomy, AU may describe asteroid approaches, comet perihelion distances, binary-star separations, or the scale of circumstellar disks. In spaceflight, mission teams often publish both kilometers and AU because spacecraft operations need precise metric values while public summaries benefit from the Solar System context.

For interstellar work, AU becomes too small. The nearest stars are hundreds of thousands of AU away, and galaxy distances would require enormous AU values. Light-years or parsecs communicate that scale more naturally. The AU-to-light-year output is still useful as a bridge: it shows why a distance that feels huge inside the Solar System is only a small fraction of a light-year.

Pitfalls and precision

Do not round 1 AU to 150 million kilometers when the task requires an exact conversion. That rounded value is fine for conversation but off by more than 400,000 kilometers. Also remember that AU is a distance unit, not a time unit, speed, or orbital period. A planet at 5 AU is not five years away, and a spacecraft at 1 AU from Earth is not automatically near the Sun-Earth average.

Scientific notation may appear in data sources. A value such as 1.495978707e11 m is the same as 149,597,870,700 m. When entering values, keep the original significant figures, convert, and then round for your report. The calculator’s display rounding does not change the unit definition.

Sources

  • NIST, SP 330 section 4, Table 8 — records the IAU 2012 definition 1 au=149,597,870,700 m.
  • NIST, Revised unit conversion factors — exact international mile value 1 mi=1609.344 m.
  • BIPM, SI Brochure, 9th edition — defines the speed of light as exactly 299,792,458 m/s.
  • International Astronomical Union, Measuring the Universe — defines a light-year as the distance light travels in one Julian year and states that a Julian year is 365.25 days, or 31.5576 million seconds. Multiplying that duration by the exact speed of light gives 1 ly=9,460,730,472,580,800 m.

Frequently asked questions

What is one astronomical unit?
One astronomical unit is exactly 149,597,870,700 meters under the modern International Astronomical Union definition. It is close to the average Earth-Sun distance, but it is no longer defined by measuring Earth's changing orbit. The fixed value makes AU conversions reproducible in astronomy, navigation, education, and mission planning.
How many kilometers are in one AU?
One AU equals 149,597,870.7 kilometers because the official meter value is divided by 1000. The calculator keeps that exact kilometer value internally before display rounding. For rough classroom comparisons, people often say about 150 million kilometers, but precise conversions should use 149,597,870.7 kilometers.
How many miles are in one AU?
Using the international mile of 1609.344 meters, one AU is about 92,955,807.273 miles. The calculator converts through meters first, so AU to miles, miles to AU, and cross-conversions with kilometers all share the same official astronomical unit base.

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