Nautical ETA Calculator
Because a knot is one nautical mile per hour, working out a voyage time is simple: divide the distance in nautical miles by your speed over ground in knots to get the time to run in hours. Add that to your departure time and you have the estimated time of arrival. Enter the leg distance, your expected speed over ground, and departure time to get the run time and ETA, including any roll past midnight.
Nautical ETA formula
Time to run (hours) = distance (nm) / speed (knots)
ETA = departure time + time to run
(1 knot = 1 nautical mile per hour)
The ETA shows the clock time and, if the arrival passes midnight, the number of days later.
Worked example
- Distance 120 nm at 10 knots over ground.
- Time to run = 120 / 10 = 12.00 hours, that is 12:00.
- Departing 08:00, the ETA is 20:00 the same day.
Nautical ETA: frequently asked questions
How do I calculate ETA at sea?
Time to run equals distance in nautical miles divided by speed in knots, because one knot is one nautical mile per hour. Add that time to your departure time to get the estimated time of arrival. For example, 120 nautical miles at 10 knots takes 12 hours.
What is a knot?
A knot is one nautical mile per hour. Because a nautical mile is 1,852 metres (1.852 km or about 1.15077 statute miles), distance in nautical miles divided by speed in knots gives the time directly in hours, with no unit conversion needed.
Does current or wind affect ETA?
Yes. The speed you should enter is speed over ground, which combines your speed through the water with the effect of current. A favourable current raises speed over ground and shortens the ETA; a foul current does the opposite. Use your expected average speed over ground for the best estimate.
How is the ETA clock time worked out?
The calculator adds the time to run to your departure time of day. If the arrival rolls past midnight it shows how many days later. Enter departure time in 24-hour format for the clearest result.
Official sources
- NOAA Office of Coast Survey: nautical charts and navigation.
- NIST: unit conversions (nautical mile = 1,852 m).
Reviewed by the CalculatorHub team, edited by James Graham, 19 June 2026. See our methodology.