Light Travel Time Calculator
How long light takes to cross a distance, in seconds, minutes, light years and astronomical units.
Results
Seconds
1.2822
s
Minutes
0.02137
min
Light years
0.0000000406
Astronomical units
0.00256956
Seconds
2.5644
s
What this tool does
The default is the distance to the Moon: light takes just over a second, which is why a video call to a lunar base would be awkward but workable, while one to Mars never could be. The round trip figure is the one that matters for radio contact, because a question and its answer both have to make the journey.
Formula
t = distance ÷ c (c = 299 792 458 m/s)
Variables
| Symbol | Meaning | Unit |
|---|---|---|
d | Distance | km |
S | Seconds | s |
MI | Minutes | min |
LY | Light years | — |
AU | Astronomical units | — |
RT | Seconds | s |
Worked example
- Distance384,400 km
- Seconds1.2822 s
- Minutes0.02137 min
- Light years0.0000000406
- Astronomical units0.00256956
- Seconds2.5644 s
Limitations
- The formula assumes ideal conditions: no friction losses, no air resistance and no efficiency losses unless you enter them.
- The default values are typical reference figures, not measurements of your situation. Replace them with your own data whenever you have it.