How this calculator works
A nautical mile is defined as exactly 1,852 metres, which is one minute of latitude on the Earth reference ellipsoid. A knot is one nautical mile per hour, so distance in nautical miles divided by speed in knots gives time in hours directly. The page also converts the distance to kilometres and statute miles, and reports the speed in kilometres per hour for comparison with road or wind speeds. The calculation assumes a constant speed over ground; currents, wind, tacking and course changes will change the real passage time.
Formula
Time (h) = distance (nmi) / speed (kn). Speed (kn) = distance (nmi) / time (h). 1 nmi = 1,852 m = 1.852 km = 1.150779 statute miles. Speed in km/h = knots x 1.852.
Worked example
A 100 nautical mile passage at 10 knots takes 10 hours. The same distance is 185.2 km or about 115.1 statute miles. A 20 nautical mile passage at 5 knots takes 4 hours.
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Frequently asked questions
Why use nautical miles at sea and in the air?
One minute of latitude is one nautical mile, which makes chart work and position calculations simpler than with statute miles. Speed in knots then gives time in hours directly when distance is in nautical miles.
Is a nautical mile the same as a sea mile?
The modern international nautical mile is exactly 1,852 metres. Older definitions based on a minute of latitude at a specific location differed slightly, so historical figures may not match exactly.
Does the calculator account for currents?
No. It uses speed over ground as a single constant. A favourable current increases speed over ground and shortens the passage, while a foul current lengthens it. Enter the speed you expect to make good.
How do I convert knots to miles per hour?
Multiply knots by 1.150779. For example, 10 knots is about 11.51 mph. The page reports speed in km/h and distance in statute miles, so you can compare with road or aviation figures.