Knots to mph converter, with km/h and nautical miles

How it works

Use nautical miles for distance and knots for speed. The international nautical mile is exactly 1,852 metres, so you multiply nautical miles by 1.852 to get kilometres. A statute mile is a different unit: exactly 1,609.344 metres. This converter always uses that international land mile, never an older regional mile. A cable here is one tenth of a nautical mile, or 185.2 metres; check the convention if you read older documents.

On a nautical chart, one minute of latitude corresponds approximately to one nautical mile. There are 60 minutes in a degree. Earth is not a perfect sphere, so a real minute of meridian arc varies slightly with latitude while the international mile stays fixed. On a Mercator chart, measure distance against the latitude scale beside your position; do not use the longitude scale as though its minutes were nautical miles.

A knot is a nautical mile per hour, not a distance. For a steady speed, distance equals speed multiplied by time in hours. Divide minutes by 60 before multiplying. To find speed, divide distance by hours; to find passage time, divide distance by speed. The triangle places distance above speed and time: cover the quantity you want to find. Keep the units consistent and use speed over ground for an arrival estimate.

For example, at 6 knots you cover 12 nautical miles in 2 hours, or 120 minutes. Depart at 09:00 and the estimated arrival is 11:00 on the same clock. Those 12 nautical miles equal 22.224 kilometres, and 6 knots equal 11.112 kilometres per hour. A current can change your speed over ground even when the log shows a steady speed through the water. Break a changing passage into legs and add their times.

The 6-minute rule follows directly from the formula: six minutes is one tenth of an hour, so the distance in cables equals the speed in knots. At 6 knots you cover 6 cables in six minutes. In three minutes you cover half that: 3 cables. These shortcuts assume constant speed and are useful for short chartwork estimates. Speed, distance and time calculations are part of RYA Day Skipper shorebased chartwork and Spanish PER navigation exercises. Show your units, distinguish minutes of time from minutes of angle, and round only the final answer.