What formula does this calculator use?

It uses the geometric horizon formula: d = sqrt(2 × R × h), where R = 6,371 km (Earth's mean radius) and h is the observer height. This gives the true geometric horizon distance without atmospheric refraction.

Does atmospheric refraction affect the result?

This calculator gives the purely geometric distance. In reality, light bends slightly through the atmosphere (refraction), which can extend the visible horizon by roughly 7–8%. For practical navigation or radio engineering, multiply the result by about 1.07 to approximate the optical horizon.

Why does height matter so much?

Because horizon distance grows with the square root of height. Doubling your height increases the horizon by about 41%, not 100%. A person at 1.7 m eye level sees about 4.7 km; climb to 100 m and the horizon extends to about 35.7 km.

Is this formula accurate for the Moon or other planets?

No — this calculator uses Earth's radius. For other bodies, the formula is the same but you would need to substitute the correct planetary radius. Earth's mean radius used here is 6,371 km.

What is the maximum input height?

The calculator accepts heights up to 8,849 m (the summit of Mount Everest, roughly 29,032 ft). Beyond that, atmospheric and orbital effects make the simple formula unreliable.

Distance To Horizon Calculator

Name: Distance To Horizon Calculator
Availability: InStock
Author: Nham Vu

Enter your height above sea level and instantly see how far away the horizon is, in kilometers or miles.

Observer Height

Height above sea level

Output unit

Kilometers (km) Miles (mi)

Quick presets

Horizon Distance

Enter a height on the left to calculate the horizon distance.

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Summary

Enter your height above sea level and instantly see how far away the horizon is, in kilometers or miles.

How it works

Enter your height above sea level (e.g., eye level on a hill or the top of a building).
Choose whether your input is in meters or feet.
Select whether you want the result in kilometers or miles.
The calculator applies the formula d = sqrt(2 × R × h) instantly.
Results update in real time as you type — no button press needed.

Use cases

Determine how far a ship can be seen from a coastal lookout.
Estimate line-of-sight range for radio or wireless antennas.
Check how far a lighthouse beam can be seen over the sea.
Plan photography or filming spots with a clear view to the horizon.
Understand horizon distance changes while hiking to higher elevations.
Educational demonstrations of Earth's curvature for science classes.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu