Use this sailing calculation as a planning or educational cross-check for navigation, wind and current, rig loads, stability, anchoring, tides, visibility, performance, or recovery under explicitly stated conditions.

Object height (ft)

Elevation of the light above sea level.

Observer height (ft)

Height of the observer's eye above the sea surface; combined heights use the one point one seven horizon coefficient.

Compute the geographic range at which a light becomes visible as one point one seven times the sum of the square roots of observer and object heights in feet. The tool evaluates the supplied inputs together and returns the named outputs below; it does not infer omitted operating conditions or change the units shown.^[1]

Geographic range (NM)

Greatest distance in nautical miles at which the object is visible.

• Actual conditions change with vessel design and loading, sea state, wind, current, tide datum, weather, chart accuracy, equipment, crew, regulations, and safety margins. Simplified formulas do not replace seamanship, approved stability data, or current navigation information.
• Use finite inputs in the displayed units and preserve more precision than the final presentation requires. Independently verify safety-critical, financial, compliance, or production decisions.

Cross-check official charts, tide and weather services, instrument data, vessel manuals, and collision regulations; maintain conservative margins and a safe alternative plan.

• AIS Range Estimate

  Estimate the range at which an automatic identification system target is received as one point one seven times the sum of the square roots of the own and target antenna heights in feet.

• VHF Range Calculator

  Estimate very high frequency radio range over water as one point one seven times the sum of the square roots of the vessel and shore antenna heights in feet.

• Horizon Range Calculator

  Compute the distance to the visible horizon in nautical miles as one point one seven times the square root of the observer height in feet.