Speed Distance Time (Nautical) Calculator
The speed-distance-time relationship is the foundation of marine navigation: Distance = Speed x Time (D = S x T). Enter any two of the three values to solve for the unknown. Speed is in knots (nautical miles per hour), distance is in nautical miles, and time is in decimal hours. This calculator is essential for estimating arrival times, fuel planning, passage timing, and tidal window calculations. Leave the field you want to calculate blank, or set it to zero, and the calculator will solve for it automatically.
Speed distance time formula
Distance (nm) = Speed (kts) * Time (hours)
Speed (kts) = Distance (nm) / Time (hours)
Time (hours) = Distance (nm) / Speed (kts)
Time in hours:minutes: Hours = floor(T); Minutes = round((T - Hours) * 60)
Leave one field blank to solve for it. All three cannot be filled simultaneously.
Practical speed-distance-time tips
- Plan passages with time to spare for weather delays, tidal windows, and traffic.
- Average speed over ground may differ from through-water speed due to current and leeway.
- GPS speed over ground is the most useful for ETA calculations as it includes all effects.
- One nm = 1,852 m. One knot = 1.151 mph. One nm = 1.852 km.
Speed distance time (nautical): frequently asked questions
What is a knot in navigation?
A knot is one nautical mile per hour. One nautical mile equals 1,852 meters or approximately 1.151 statute miles. The term comes from the historical method of measuring speed by counting knots on a line thrown overboard.
How do I calculate ETA from distance and speed?
Time (hours) = Distance (nm) / Speed (knots). For example, 120 nm at 8 knots takes 15 hours. Convert decimal hours to hours and minutes by multiplying the decimal part by 60. 15.5 hours = 15 hours 30 minutes.
What is the 60D-ST rule?
The 60D-ST rule (or 60:D=S*T) is the fundamental navigation triangle: Distance = Speed * Time. Rearranging gives Speed = Distance / Time and Time = Distance / Speed. All three formulas use the same relationship.
How do I convert speed over ground to speed through water?
Speed over ground (SOG) from GPS includes the effect of current. Speed through water (STW) from a paddlewheel log does not. To find the current component, subtract STW from SOG vectorially. For simple cases, the difference in speeds along the course line approximates the current.
What are typical boat speeds by vessel type?
Displacement sailboats typically cruise at 5-8 knots. Motor cruisers run 12-25 knots. Planing powerboats reach 30-50 knots. Commercial ships cruise at 12-25 knots. These are rough guides; fuel economy and sea state vary considerably.
Official sources
- National Geospatial-Intelligence Agency: Bowditch American Practical Navigator (Pub. 9).
- US Coast Guard: USCG Navigation Center.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.