Tool
Voyage-time calculator
Estimate how long a sea passage would take from distance, average speed in knots and the number of hours the vessel travels each day.
Enter a distance and speed to calculate an estimated passage time.
How the calculation works
A knot equals one nautical mile per hour, so travel time in hours equals nautical miles divided by knots. The calculator then divides the total hours under way by the number of sailing hours you specify for each day.
For example, a vessel covering 240 nautical miles at an average of 8 knots needs 30 hours under way. If it travels continuously, that is about 1.25 days. If it travels only 10 hours per day, the same amount of time under way spans three sailing days.
Why historical voyages need ranges
Real voyages rarely maintain one exact speed. Wind, current, sea state, sail changes, navigation decisions, repairs, stops and weather delays all affect progress. Historical ships introduce additional uncertainty because surviving evidence often gives only broad indications of performance.
Use this calculator to compare scenarios, not to assign an exact arrival time to an ancient voyage. A historically responsible estimate should usually present a range and explain the conditions that could shift the result.