Convert astronomical units to kilometers

Content last reviewed:

Enter a value in astronomical units and the converter shows the distance in kilometers. One astronomical unit is exactly 149,597,870.7 km, so 2 au comes to 299,195,741.4 km. The page also lists planet distances from the Sun and scale models of the Solar System.

au

The field also accepts scientific notation, for example 6.5e-7 or 6.5 × 10⁻⁷.

km
to

What is an astronomical unit?

The astronomical unit is used mainly to measure distances within the Solar System or around other stars[1]. It was originally conceived as the average distance between Earth and the Sun, the average of Earth's aphelion and perihelion (its farthest and closest points from the Sun)[1].

Since 2012 the unit has had a conventional value of exactly 149,597,870,700 meters. The XXVIII General Assembly of the International Astronomical Union set that value in Resolution B2 and recommended a single symbol for the unit, au[2]. Journals of the American Astronomical Society and the Royal Astronomical Society later adopted that symbol[1].

The astronomical unit is a non-SI unit. The SI Brochure of the International Bureau of Weights and Measures lists it in its table of non-SI units with the value 1 au = 149,597,870,700 m[3].

Silhouettes of observatory buildings on a mountain summit against an orange band of sky after sunset
Observatory buildings on a summit above the clouds, photographed after sunset. The photographer describes the picture as the Daniel K. Inouye Solar Telescope. The Sun that this telescope observes is about one astronomical unit away from Earth. Photo: Sam Goodgame, Unsplash.

How many kilometers are in an astronomical unit?

An astronomical unit is exactly 149,597,870.7 kilometers. That figure is the definition in meters divided by 1,000.

Rounded, the unit is 150 million kilometers, or 93 million miles[4]. With the exact value, two astronomical units come to 299,195,741.4 kilometers. Half an astronomical unit is 74,798,935.35 kilometers.

Ten astronomical units equal 1,495,978,707 kilometers. For whole tens you only move the decimal point of the constant to the right, so no written multiplication is needed.

In scientific notation one astronomical unit is 1.495978707 × 10⁸ km. The notation keeps one digit before the decimal point, and the exponent gives the number of places the point moves to the right.

Light travels one astronomical unit in about 499 seconds, slightly more than 8 minutes 19 seconds[1].

The converter above works in both directions and updates the result as you type. It shows small values with ten significant digits, counted from the first non-zero digit.

How do you convert astronomical units to kilometers? Formula and examples

The conversion uses one constant: an astronomical unit is 149,597,870.7 kilometers. To turn astronomical units into kilometers, multiply by that constant.

The formula: kilometers = astronomical units × 149,597,870.7. The other way: astronomical units = kilometers ÷ 149,597,870.7.

Three examples show different scales. The semi-major axis of Jupiter's orbit is about 5.2 astronomical units[5]. Multiplied by the constant, that gives 777,908,927.64 kilometers. A value of 0.04 au is 5,983,914.828 kilometers. One hundred astronomical units come to 14,959,787,070 kilometers, almost 15 billion.

For a result in meters, multiply by 149,597,870,700, or convert kilometers with the km to meters converter. You can convert a distance given in kilometers into astronomical units with the km to au converter.

How many kilometers are in a given number of astronomical units?

The table covers fractions of an astronomical unit, whole values and distances of hundreds of units. Each result is the number of astronomical units multiplied by 149,597,870.7, given in full and in scientific notation.
Astronomical unitsKilometersScientific notation
0.001 au149,597.8707 km1.495978707 × 10⁵ km
0.01 au1,495,978.707 km1.495978707 × 10⁶ km
0.04 au5,983,914.828 km5.983914828 × 10⁶ km
0.05 au7,479,893.535 km7.479893535 × 10⁶ km
0.1 au14,959,787.07 km1.495978707 × 10⁷ km
0.2 au29,919,574.14 km2.991957414 × 10⁷ km
0.25 au37,399,467.675 km3.739946767 × 10⁷ km
0.3 au44,879,361.21 km4.487936121 × 10⁷ km
0.39 au58,343,169.573 km5.834316957 × 10⁷ km
0.4 au59,839,148.28 km5.983914828 × 10⁷ km
0.5 au74,798,935.35 km7.479893535 × 10⁷ km
0.72 au107,710,466.904 km1.077104669 × 10⁸ km
0.75 au112,198,403.025 km1.12198403 × 10⁸ km
1 au149,597,870.7 km1.495978707 × 10⁸ km
1.5 au224,396,806.05 km2.24396806 × 10⁸ km
1.52 au227,388,763.464 km2.273887635 × 10⁸ km
1.8 au269,276,167.26 km2.692761673 × 10⁸ km
2 au299,195,741.4 km2.991957414 × 10⁸ km
2.5 au373,994,676.75 km3.739946768 × 10⁸ km
2.77 au414,386,101.839 km4.143861018 × 10⁸ km
3 au448,793,612.1 km4.487936121 × 10⁸ km
4 au598,391,482.8 km5.983914828 × 10⁸ km
5 au747,989,353.5 km7.479893535 × 10⁸ km
5.2 au777,908,927.64 km7.779089276 × 10⁸ km
6 au897,587,224.2 km8.975872242 × 10⁸ km
8 au1,196,782,965.6 km1.196782966 × 10⁹ km
9.54 au1,427,163,686.478 km1.427163686 × 10⁹ km
10 au1,495,978,707 km1.495978707 × 10⁹ km
15 au2,243,968,060.5 km2.243968061 × 10⁹ km
19.2 au2,872,279,117.44 km2.872279117 × 10⁹ km
20 au2,991,957,414 km2.991957414 × 10⁹ km
25 au3,739,946,767.5 km3.739946767 × 10⁹ km
30 au4,487,936,121 km4.487936121 × 10⁹ km
30.07 au4,498,407,971.949 km4.498407972 × 10⁹ km
39.5 au5,909,115,892.65 km5.909115893 × 10⁹ km
40 au5,983,914,828 km5.983914828 × 10⁹ km
50 au7,479,893,535 km7.479893535 × 10⁹ km
100 au14,959,787,070 km1.495978707 × 10¹⁰ km
170 au25,431,638,019 km2.543163802 × 10¹⁰ km
500 au74,798,935,350 km7.479893535 × 10¹⁰ km
1,000 au149,597,870,700 km1.495978707 × 10¹¹ km
Read 1.495978707 × 10⁸ km as 1.495978707 multiplied by one hundred million. To turn a result into miles, use the km to miles converter.

How far are the planets from the Sun in kilometers?

A planet's average distance from the Sun is described by the semi-major axis of its orbit, half of the longest diameter of the ellipse the planet travels along. The values in astronomical units come from a Jet Propulsion Laboratory table, and the kilometers are those values multiplied by 149,597,870.7.
PlanetSemi-major axisKilometersMillions of kilometers
Mercury0.38709927 au57,909,227 km57.9 million km
Venus0.72333566 au108,209,475 km108.2 million km
Earth (Earth–Moon barycenter)1.00000261 au149,598,261 km149.6 million km
Mars1.52371034 au227,943,822 km227.9 million km
Jupiter5.202887 au778,340,817 km778.3 million km
Saturn9.53667594 au1,426,666,414 km1,426.7 million km
Uranus19.18916464 au2,870,658,171 km2,870.7 million km
Neptune30.06992276 au4,498,396,417 km4,498.4 million km
The JPL table gives orbital elements (the parameters that describe the shape and position of an orbit) valid for 1800 to 2050. Its row for Earth describes the Earth–Moon barycenter, the center of mass of the Earth–Moon system[5]. If you find planet distances given in miles, convert them to kilometers with the miles to km converter.

How many meters does an astronomical unit take up in a scale model of the Solar System?

A model's scale is the factor by which its distances were reduced. At 1:1,000,000,000 one astronomical unit, 149,597,870,700 meters, becomes 149.6 meters.
Model scaleOne astronomical unit in the modelNeptune in the model
1:100,000,0001.496 km44.98 km
1:1,000,000,000149.6 m4.498 km
1:10,000,000,00014.96 m449.8 m
1:100,000,000,0001.496 m44.98 m
1:1,000,000,000,00014.96 cm4.498 m
The Voyage project describes its one to 10-billion scale model of the Solar System on the National Mall in Washington, DC, as spanning 600 meters (2,000 feet) from the National Air and Space Museum to the Smithsonian Castle Building[6]. At that scale one astronomical unit is 14.96 meters.

What other values of the astronomical unit in kilometers will you find?

Before the astronomical unit had a conventional value, its length in kilometers was derived from observations. Values from before 2012 differ from today's definition by a few meters.
Source of the valueValueDifference from the 2012 definition
International Bureau of Weights and Measures, 2006149,597,870.691 km9 m less
IAU System of Astronomical Constants, 2009149,597,870.7 km ± 3 msame figure with a 3 m uncertainty
IAU definition, 2012149,597,870.7 kmexact value
Rounded figure150,000,000 km402,129.3 km more
The International Bureau of Weights and Measures reported 149,597,870.691 km in 2006[1]. The IAU 2009 System of Astronomical Constants gave 149,597,870,700 m with an uncertainty of 3 m[2]. The 2012 resolution made that figure exact[2].

How do you convert astronomical units to kilometers in a spreadsheet?

For a single value the converter is quicker. For a whole column of distances, a spreadsheet does the job with one formula copied down the column.

  1. Excel: multiply by the constant

    The CONVERT function handles light-years, entered as "ly", and parsecs, entered as "pc"[7]. Astronomical units need a plain multiplication. With a value in cell A1, type =A1*149597870.7 and the result is in kilometers.

  2. Scientific format for long results

    Results have nine or more digits, and a shorter format makes them easier to read. Select the cells, go to Home, in the Number group click the small More button next to Number, and in the Category list click Scientific. Excel then shows 1.50E+08 instead of 149597870.7[8].

  3. Checking precision

    Excel keeps numbers to a maximum precision of 15 digits[8]. The constant 149597870.7 has ten digits, so it stays within that limit. Type 1 in cell A1 and check that the formula returns 149597870.7.

Convert other units to Kilometers

miles to kmmeters to kmcm to kmmm to kmdm to kmyards to km

Sources

  1. Astronomical unit — Wikipedia
  2. Resolution B2 on the re-definition of the astronomical unit of length — International Astronomical Union
  3. The International System of Units (SI Brochure), Table 8 — Bureau International des Poids et Mesures
  4. Light-year — Wikipedia
  5. Approximate Positions of the Planets — NASA Jet Propulsion Laboratory
  6. Voyage on the National Mall — Voyage Scale Model Solar System
  7. CONVERT function — Microsoft
  8. Display numbers in scientific (exponential) notation — Microsoft

Every figure in the tables was computed from the unit definitions and checked arithmetically before publication. Historical values and the names of local units come from the sources listed above.

Content last reviewed: · written and checked by the Arteon team

Common questions about converting astronomical units to kilometers

How many km is 1 au?

One astronomical unit is exactly 149,597,870.7 km. That value has applied since 2012, when the International Astronomical Union set the unit at 149,597,870,700 meters.

Is an astronomical unit the distance from Earth to the Sun?

Approximately. The unit has a fixed length, while Earth's distance from the Sun varies over the year between 0.9832898912 and 1.0167103335 au[1]. In kilometers that is roughly 147.1 to 152.1 million. To turn a distance in kilometers back into astronomical units, use the km to au converter.

Why do some calculators give 149,597,870.691 km?

That is the value the International Bureau of Weights and Measures reported in 2006, before the 2012 definition. It differs from today's value by 9 meters, so the result for one astronomical unit changes only in the tenth significant digit.

Why does the astronomical unit have a conventional value?

Distance measurements in the Solar System became precise enough that astronomy no longer needs distance ratios. The 2012 resolution of the International Astronomical Union gives this reason and fixes the unit as a conventional length of 149,597,870,700 meters.

How do you write an astronomical unit in kilometers in scientific notation?

One astronomical unit is 1.495978707 × 10⁸ km. The converter shows this under the result field in the Scientific notation line, rounded to six digits: 1.49598 × 10⁸ km.

Can I type decimals and scientific notation?

Yes. You can type a decimal such as 1.52, as well as 1.5e8 or 1.5 × 10⁸. The result appears as you type, with no separate button to click.

Arteon free tool screenshot: Convert astronomical units to kilometers

Have a question or suggestion?

If you spotted an error in the tables or have an idea to improve the converter, write to us — we reply within 24 hours.