What is the exact value of 1 au in km?

The IAU defines 1 astronomical unit as exactly 149,597,870,700 metres (Resolution B2, 2012). That is 149,597,870.7 kilometres per au. This calculator’s default demo (1 au) shows 149,597,870.7 km and 92,955,807.3 miles. 1 au is exact by IAU definition (149,597,870,700 m). Light-year and parsec values use conventional metre equivalents, not additional IAU exact definitions.

What is the official IAU definition of 1 au?

Since 2012 the astronomical unit is a fixed length: 149,597,870,700 m, not a measured mean Earth–Sun distance. It replaced older definitions tied to the Gaussian gravitational constant so ephemerides use a consistent scale.

How do you convert au to km?

km = au × 149,597,870.7. Example: 9.5 au (Saturn scale) ≈ 1,421,179,771.65 km. 5.2 au (Jupiter) ≈ 777,908,927.64 km.

How many miles is 1 astronomical unit?

1 au ≈ 92,955,807.273 miles, from 149,597,870,700 m ÷ 1,609.344 m/mi. Often rounded to about 93 million miles in popular science writing.

How many astronomical units are in a light year?

Using the conventional light-year length in this calculator, 1 ly ≈ 63,241 au (about 63,241 au). Conversely, 1 au ≈ 0.00001581 ly.

How many au are in a parsec?

By definition, 1 parsec ≈ 206,266.3 au (about 206,265 au). Enter 1 pc in the calculator for km, miles, and au in one step.

How far is Earth from the Sun in au?

Earth’s orbit is elliptical: roughly 0.983 au at perihelion and about 1.017 au at aphelion. The unit “1 au” is a standard reference scale close to the average separation.

Is the astronomical unit an SI unit?

No—it is a non-SI unit accepted for astronomy with an exact conversion to metres defined by the IAU. SI uses the metre; au is a practical Solar System yardstick.

What is 9.5 au to km?

Multiply: 9.5 × 149,597,870.7 ≈ 1,421,179,771.65 km (Saturn’s orbit is often quoted near 9.5 au).

Can I convert km to au?

Yes—enter kilometres and read au, or use au = km ÷ 149,597,870.7. Example: 149,597,870.7 km = 1 au exactly.

How was the astronomical unit measured historically?

Parallax, radar ranging to planets, and spacecraft telemetry refined the Earth–Sun distance before the IAU fixed the numeric value in 2012 so the constant no longer drifts with new measurements.

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IAU 2012 · Solar System distances

Astronomical Unit Calculator

Quick answer — 1 au in km

1 au = 149,597,870,700 m exactly (IAU 2012) = 149,597,870.7 km = 92,955,807.3 mi. 9.5 au ≈ 1,421,179,772 km. 1 ly ≈ 63,241 au.

Exact definition: 1 au = 149,597,870,700 m
au → km: km = au × 149,597,870.7
Jupiter ≈ 5.2 au: ≈ 777,908,928 km
Light years: Light year conversion

Free astronomical unit calculator and au to km converter—IAU exact metres, miles, light years, parsecs, and Sun radii. More on our Conversion hub.

Last updated October 9, 2026

IAU 2012 exact 1 au in metres

au, km, mi, ly, pc, R☉

Solar System scenario distances

Planetary distances in scenario examples are typical mean or rounded values—not ephemeris precision.

Astronomical Unit Calculator

Convert between astronomical units, meters, kilometers, miles, light years, parsecs, and more

Distance

Conversion Results

Astronomical Units

1 au

Light Years

0.00001581 ly

Parsecs

0.00000485 pc

Sun Radii

214.834521 R☉

Metric Units

Meters

149,597,870,700 m

Kilometers

149,597,870.7 km

Imperial/US Units

Miles

92,955,807.27 mi

Key Facts:

• 1 au = 149,597,870,700 m exactly (IAU 2012 definition)
• 1 au ≈ 149.6 million km ≈ 93 million miles
• 1 au = 0.000015813 light years
• 1 light year = 63,241 astronomical units
• 1 parsec ≈ 206,264.8 astronomical units
• Earth-Sun distance averages about 1 au

AU conversion scenarios (computed)

Same factors as the calculator—including 9.5 au to km and the exact 1 au definition.

Astronomical unit conversion scenario summary
Scenario	Input	Kilometres	Miles	au
1 au (IAU definition)	1 au	149,597,870.7 km	92,955,807.27 mi	1 au
1 au in km / miles	1 au	149,597,870.7 km	92,955,807.27 mi	1 au
Mars ≈ 1.5 au	1.5 au	224,396,806.05 km	139,433,710.91 mi	1.5 au
Jupiter ≈ 5.2 au	5.2 au	777,908,927.64 km	483,370,197.82 mi	5.2 au
Saturn ≈ 9.5 au	9.5 au	1,421,179,771.65 km	883,080,169.09 mi	9.5 au
1 light year	1 ly	9,460,700,000,000 km	5,878,606,438,399.75 mi	63,240.873388 au
1 parsec	1 pc	30,857,000,000,000 km	19,173,650,878,867.41 mi	206,266.304832 au
149,597,870,700 m	149597870700 m	149,597,870.7 km	92,955,807.27 mi	1 au

Terms at a glance

Astronomical unit (au): Standard yardstick for Solar System distances; fixed length in metres since 2012.
Light year (ly): Distance light travels in one Julian year at c—used for stars; ≈ 63,241 au.
Parsec (pc): Distance where 1 au subtends 1 arcsecond; ≈ 206,265 au and ≈ 3.26 ly.
Solar radius (R☉): Roughly 696,340 km—handy for comparing sizes to the Sun.

How astronomical unit conversion works

All paths go through metres. The au is exact; other astronomical lengths use conventional metre equivalents for teaching and quick estimates.

1. IAU definition
1 au = 149,597,870,700 m exactly (Resolution B2, 2012).
2. Convert input to metres
m = value × (metres per chosen unit).
3. Metres to au
au = m ÷ 149,597,870,700.
4. Kilometres and miles
km = au × 149,597,870.7; mi = m ÷ 1,609.344.
5. Light years and parsecs
ly = m ÷ 9460700000000000; pc = m ÷ 30857000000000000 (conventional factors).

Limitations

1 au is exact by IAU definition (149,597,870,700 m). Light-year and parsec values use conventional metre equivalents, not additional IAU exact definitions.
Planetary distances in scenario examples are typical mean or rounded values—not ephemeris precision.
Earth–Sun distance varies with orbit (roughly 0.983–1.017 au); “1 au” is a standard scale, not today’s instantaneous separation.

Sources & references

IAU — Resolution B2 (2012)Redefinition of the astronomical unit in metres.
NIST — SI and accepted non-SI unitsMetre as SI base; au linked via exact conversion.

Worked example

Convert 1 au to km and miles

IAU exact definition

m = 1 × 149,597,870,700 = 149,597,870,700 m

km = m ÷ 1,000 = 149,597,870.7 km

mi = m ÷ 1,609.344 = 92,955,807.273 mi

Light-time across 1 au is about 499 seconds (~8.3 minutes) at c.

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IAU 2012 · Solar System distances

Astronomical Unit Calculator

Quick answer — 1 au in km

1 au = 149,597,870,700 m exactly (IAU 2012) = 149,597,870.7 km = 92,955,807.3 mi. 9.5 au ≈ 1,421,179,772 km. 1 ly ≈ 63,241 au.

Exact definition: 1 au = 149,597,870,700 m
au → km: km = au × 149,597,870.7
Jupiter ≈ 5.2 au: ≈ 777,908,928 km
Light years: Light year conversion

Free astronomical unit calculator and au to km converter—IAU exact metres, miles, light years, parsecs, and Sun radii. More on our Conversion hub.

Last updated October 9, 2026

IAU 2012 exact 1 au in metres

au, km, mi, ly, pc, R☉

Solar System scenario distances

Planetary distances in scenario examples are typical mean or rounded values—not ephemeris precision.

Astronomical Unit Calculator

Convert between astronomical units, meters, kilometers, miles, light years, parsecs, and more

Distance

Conversion Results

Astronomical Units

1 au

Light Years

0.00001581 ly

Parsecs

0.00000485 pc

Sun Radii

214.834521 R☉

Metric Units

Meters

149,597,870,700 m

Kilometers

149,597,870.7 km

Imperial/US Units

Miles

92,955,807.27 mi

Key Facts:

• 1 au = 149,597,870,700 m exactly (IAU 2012 definition)
• 1 au ≈ 149.6 million km ≈ 93 million miles
• 1 au = 0.000015813 light years
• 1 light year = 63,241 astronomical units
• 1 parsec ≈ 206,264.8 astronomical units
• Earth-Sun distance averages about 1 au

AU conversion scenarios (computed)

Same factors as the calculator—including 9.5 au to km and the exact 1 au definition.

Astronomical unit conversion scenario summary
Scenario	Input	Kilometres	Miles	au
1 au (IAU definition)	1 au	149,597,870.7 km	92,955,807.27 mi	1 au
1 au in km / miles	1 au	149,597,870.7 km	92,955,807.27 mi	1 au
Mars ≈ 1.5 au	1.5 au	224,396,806.05 km	139,433,710.91 mi	1.5 au
Jupiter ≈ 5.2 au	5.2 au	777,908,927.64 km	483,370,197.82 mi	5.2 au
Saturn ≈ 9.5 au	9.5 au	1,421,179,771.65 km	883,080,169.09 mi	9.5 au
1 light year	1 ly	9,460,700,000,000 km	5,878,606,438,399.75 mi	63,240.873388 au
1 parsec	1 pc	30,857,000,000,000 km	19,173,650,878,867.41 mi	206,266.304832 au
149,597,870,700 m	149597870700 m	149,597,870.7 km	92,955,807.27 mi	1 au

Terms at a glance

Astronomical unit (au): Standard yardstick for Solar System distances; fixed length in metres since 2012.
Light year (ly): Distance light travels in one Julian year at c—used for stars; ≈ 63,241 au.
Parsec (pc): Distance where 1 au subtends 1 arcsecond; ≈ 206,265 au and ≈ 3.26 ly.
Solar radius (R☉): Roughly 696,340 km—handy for comparing sizes to the Sun.

How astronomical unit conversion works

All paths go through metres. The au is exact; other astronomical lengths use conventional metre equivalents for teaching and quick estimates.

1. IAU definition
1 au = 149,597,870,700 m exactly (Resolution B2, 2012).
2. Convert input to metres
m = value × (metres per chosen unit).
3. Metres to au
au = m ÷ 149,597,870,700.
4. Kilometres and miles
km = au × 149,597,870.7; mi = m ÷ 1,609.344.
5. Light years and parsecs
ly = m ÷ 9460700000000000; pc = m ÷ 30857000000000000 (conventional factors).

Limitations

1 au is exact by IAU definition (149,597,870,700 m). Light-year and parsec values use conventional metre equivalents, not additional IAU exact definitions.
Planetary distances in scenario examples are typical mean or rounded values—not ephemeris precision.
Earth–Sun distance varies with orbit (roughly 0.983–1.017 au); “1 au” is a standard scale, not today’s instantaneous separation.

Sources & references

IAU — Resolution B2 (2012)Redefinition of the astronomical unit in metres.
NIST — SI and accepted non-SI unitsMetre as SI base; au linked via exact conversion.