Distance to Horizon at Sea Calculator
Fill in the values and the answer updates as you type.
How the Distance to Horizon at Sea Calculator works
Distance to the horizon in nautical miles ≈ 1.17 × the square root of the height in feet, which includes the usual bending of light by the air. The distance at which an object first rises over the horizon is the sum of the two horizon distances, one for your eye and one for the top of the object. Light lists give the geographic range of a lighthouse for a 15 ft eye height, so use this to adjust it for your own boat. Haze, waves, and the curve of the earth all matter, so treat the answer as an estimate. Example: with Eye height above the water 6, Height of the object you look at 40, and Height unit ft, the result is Distance to your horizon (NM) = 2.9; Distance to your horizon (km) = 5.3; Distance to see the object first (NM) = 10.3.
Inputs and results
The Distance to Horizon at Sea Calculator takes 3 inputs and gives 5 results.
What you enter
- Eye height above the water — starts at 6.
- Height of the object you look at — starts at 40.
- Height unit — starts at ft. Choose from: ft and m.
What you get
- Distance to your horizon (NM)
- Distance to your horizon (km)
- Distance to see the object first (NM)
- Distance to see the object first (km)
- Horizon distance from the object (NM)
Example: Distance to Horizon at Sea Calculator with the starting values
With eye height above the water 6, height of the object you look at 40 and height unit ft, the calculator returns:
| Distance to your horizon (NM) | 2.9 |
|---|---|
| Distance to your horizon (km) | 5.3 |
| Distance to see the object first (NM) | 10.3 |
| Distance to see the object first (km) | 19 |
| Horizon distance from the object (NM) | 7.4 |
Change any value above and the results update straight away.
Distance to Horizon at Sea Calculator FAQ
How do I use the Distance to Horizon at Sea Calculator?
Enter eye height above the water, height of the object you look at and height unit in the fields, then read distance to your horizon (nm), distance to your horizon (km), distance to see the object first (nm) and distance to see the object first (km) in the result panel. The answer updates as you type, and you can press Calculate or Enter to refresh it. Use “Copy link” to share your exact numbers with someone else.
What does the Distance to Horizon at Sea Calculator calculate?
How far you can see over water, and when a light or landmark appears. It returns distance to your horizon (nm), distance to your horizon (km), distance to see the object first (nm) and distance to see the object first (km) from the 3 values you provide.
What values does the Distance to Horizon at Sea Calculator start with?
It opens with eye height above the water 6, height of the object you look at 40 and height unit ft so you can see a working result straight away. Replace them with your own numbers, or press Reset to return to these starting values.
Is the Distance to Horizon at Sea Calculator free and private?
Yes. It is free, needs no account, and runs in your browser, so nothing you type is sent to or stored on our servers. See the Privacy Policy for details.
Can I rely on the Distance to Horizon at Sea Calculator for important decisions?
Treat the result as a well-rounded estimate. Real situations often have details a general calculator cannot know, so confirm important decisions with a qualified professional. See the Disclaimer for more.