Distance to Horizon Calculator
Enter your eye height above the water to find how far you can see to the horizon, in nautical miles, statute miles and kilometres.
How to calculate distance to the horizon
- Measure your eye height above the water, in feet or metres.
- Enter the height in either unit below.
- Read the distance to the horizon in nautical miles, statute miles and kilometres.
Examples
Standing on deck, 9 ft eye height
eyeHeightFt = 9
About 5.91 km, 3.19 nautical miles or 3.67 statute miles
Frequently asked questions
How far away is the horizon at sea?
It depends on your eye height. From about 9 feet up the horizon is roughly 3.2 nautical miles away. The higher you stand, the farther you can see.
What formula does this use?
It uses the standard-refraction approximation: distance in kilometres equals 3.57 times the square root of your eye height in metres, then converts to miles.
Why does refraction matter?
The atmosphere bends light slightly downward, so the true horizon is a little farther than pure geometry predicts. The 3.57 coefficient already includes typical refraction.
How far can I see a tall object like a lighthouse?
Add the horizon distance for your eye height to the horizon distance for the object's height. Both of you see over the same curved surface.
Does this work on land too?
Yes, over flat, unobstructed ground the same formula applies. Hills, buildings and trees will of course block the view sooner.
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