Dipping Distance of Light Calculator
The dipping distance is the range at which a light sits exactly on the horizon, rising into view as you close it and dipping below as you draw away. Note the instant a charted light dips, take a bearing of it, and you have a distance-and-bearing fix from a single object. The distance is the light's geographic range: 1.17 times the square root of the light height plus 1.17 times the square root of your height of eye, with heights in feet. Enter both heights and this calculator returns the dipping distance and each horizon component.
Dipping distance formula
Light horizon = 1.17 x sqrt(light height in feet)
Eye horizon = 1.17 x sqrt(height of eye in feet)
Dipping distance = light horizon + eye horizon (nm)
Kilometers = nautical miles x 1.852
The dipping distance is the geographic range of the light. The 1.17 coefficient converts a height in feet to a horizon distance in nautical miles, including standard refraction.
Dipping fix notes
- Time the exact moment the light rises or dips at the sea horizon.
- Take a compass bearing at the same instant for a one-object fix.
- A higher height of eye raises the light at a greater range.
- Use the charted height of the light from the U.S. Coast Guard Light List.
- Heights are in feet to match the 1.17 coefficient.
Dipping distance: frequently asked questions
What is the dipping distance of a light?
The dipping distance is the range at which a navigational light is exactly on the horizon: it rises into view as you approach and dips below the horizon as you recede. Taking a bearing of a light at the moment it dips gives a position line at a known distance, a classic coastal fix.
How is dipping distance calculated?
It is the geographic range of the light. With heights in feet, dipping distance in nautical miles equals 1.17 times the square root of the light height plus 1.17 times the square root of the height of eye. This is identical to the geographic range formula in the U.S. Coast Guard Light List.
How do I use a dipping distance for a fix?
Watch a charted light and note the instant it rises above or dips below the horizon. At that moment your distance from the light equals the calculated dipping distance. Combined with a compass bearing of the light, this gives a single-object distance-and-bearing fix.
Why does my height of eye matter?
A higher viewpoint sees farther over the curved Earth, so you raise the light sooner and lose it later. The height-of-eye term adds your horizon distance to the light's horizon distance. A lookout aloft will report the light dipping at a greater range than someone at deck level.
Is dipping distance affected by the light's brightness?
No. Dipping distance is purely geometric, set by the curvature of the Earth and the two heights. Brightness governs the luminous range instead. In clear weather a strong light is usually limited by its dipping (geographic) distance, so the dipping fix is reliable.
Official sources
- U.S. Coast Guard Navigation Center: Navigation Center and Light List.
- NOAA Office of Coast Survey: Nautical Charts.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.