Distance to horizon calculator
Enter the observer's eye height, and add a target height to find the farthest distance at which its top shows above the horizon.
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Processing and privacy: The result is calculated inside your browser and your data is not sent to any server.
How to use it
- Enter observer eye height and target height.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
d = √(2Rh + h²) with Earth radius R = 6371 km. Standard refraction uses an effective radius of 7R ÷ 6. Target visibility = observer horizon + target horizon.
Example
Inputs: Observer eye height = 1.7 m, Target height = 0 m. Result: Geometric distance to horizon: 4.654 km; With standard refraction: 5.027 km; Geometric distance in miles: 2.892 mi.
Limits and caveats
- Assumes a smooth spherical Earth with no hills or buildings in the way.
- Real refraction varies with temperature and pressure; the standard value is a common approximation.
Questions about this tool
How far is the horizon for someone on the beach?
For eyes at 1.7 m the horizon is about 4.7 km away geometrically, about 5 km with refraction.
Why does refraction add distance?
The atmosphere bends light slightly around Earth's curve, so you see a little farther.
How do I find how far a lighthouse is visible?
Enter its height as the target; the tool adds your horizon and its horizon to give the farthest distance its top shows.