Speed of Light Calculator
Calculate how long it takes light to travel a given distance, using the exact speed of light in a vacuum.
What this calculator finds
The speed of light in a vacuum is an exact physical constant, c = 299,792,458 meters per second. This calculator uses that constant to find how long it takes light (or any signal traveling at light speed, such as a radio wave) to cover a given distance: time = distance / c.
How this calculator works
Enter a distance and choose its unit (kilometers, miles, astronomical units, or light-years). The calculator converts the distance to meters and divides by the speed of light to give the travel time in seconds, also shown in minutes.
This calculation assumes travel through a vacuum; light travels slightly slower through air, water, glass, or other media. For general educational and astronomy planning purposes.