Light Travel Time Calculator
Estimate how long light takes to travel a distance. Choose a preset (planet distances) or enter a custom distance.
Light travel time
Time (readable)
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Exact seconds
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Using c = 299,792.458 km/s
Distance used
This is a simplified estimate. Real spacecraft signals can be slower due to routing and atmosphere, but light in vacuum travels at c.
How we calculate
Time = distance / c. We convert your input to kilometers, then divide by the speed of light.