AU Converter
Swap AU, km, miles, and light-minutes.
What it does
The astronomical unit pins solar system distances to one exact meter count instead of a wobbling Earth orbit average. Mission plans, ephemerides, and textbooks all speak au with kilometers and light time beside it.
The tool above takes a distance in au, km, miles, or light-minutes. It returns au with kilometers and light-minutes, so press kit figures translate either way.
One au converts to 149,597,870.7 km with 8.317 light-minutes. Half an au gives 74,798,935.4 km with 4.158 min, and 92,955,807.27 miles returns exactly 1 au.
The definition follows IAU 2012 Resolution B2 with NASA JPL parameter tables matching: 149,597,870,700 m exactly and 499.004783836 s of light time per au.
How to use
- Enter the distance number.
- Pick its unit: au, km, miles, light-min.
- Read au first.
- Read kilometers beside it.
- Read light-minutes for delay sense.
- Round only at display time.
Formula
- au
- 149,597,870,700 m exactly, IAU 2012.
- c
- 299,792,458 m/s exact, behind light time.
- 499.0 s
- Light seconds per au in vacuum.
Au is now a fixed convention, not a measured Earth distance, so it never drifts with orbit refinements. Light time assumes vacuum speed; atmosphere and Shapiro delay sit outside.
Worked example
Example: 1 au
Defaults: value 1, unit astronomical units.
- km: 1 x 149,597,870.7 = 149,597,870.7 km.
- Light: 499.0048 / 60 = 8.317 min.
- Tool shows 1 au, 149,597,870.7 km, 8.317 light-min.
- Half au: 74,798,935.4 km, 4.158 min.
- Miles check 92,955,807.27 returns 1 au.
Reference table
| Distance | Kilometers | Light time |
|---|---|---|
| 0.5 au | 74,798,935.4 km | 4.158 light-min |
| 1 au | 149,597,870.7 km | 8.317 light-min |
| 2 au | 299,195,741.4 km | 16.633 light-min |
Limits
- Vacuum light speed assumed.
- Fixed convention, not live orbit.
- Relativistic delays excluded.
- Display rounding only at the end.
Common mistakes
- Calling au the current Earth gap.
- Uppercase AU against IAU style.
- Light time with slowdown media.
- Rounding meters before converting.
- Miles factor from memory.
Try it yourself
Quick checks. Answers sit tucked under each question.
0.5 au in km and light?
74,798,935.4 km with 4.158 light-min.
92,955,807.27 miles?
Exactly 1 au back.
Light seconds per au?
499.0 s in vacuum.
Questions
How far is 1 au?
149,597,870.7 km, about 8.317 light-minutes.
Why lowercase au?
IAU style fixes lowercase since the 2012 resolution.
Exact or measured?
Exact by definition: 149,597,870,700 m, no error bars.
Earth always 1 au out?
No, orbit varies; au is the ruler, not the reading.
Mars in au?
About 1.52 au average, varying with both orbits.
Light time use?
One way signal delay for spacecraft commanding.