To convert from knots to miles per hour, multiply the speed in knots by the number of feet per knot, and divide by the number of feet per mile. The term "knot" refers to speed at sea and dates back to the use of a rope to determine speed.
- Find the current speed in knots
Determine the current speed of the ship or airplane in knots, using the gauge if available, as modern boats use ultrasonic sensors or Doppler technology to determine speed. Calculate speed in knots manually if necessary. Tie knots in a rope every 14.4 meters, attaching one end to the stern of the boat and the other end to a wooden board. Drop the board into the water, and hold the slack of the rope in your hands. Have an assistant start a 30-second timer, counting the number of knots that go through your fingers during that time period. Multiply the number of knots by 1.85 to determine the speed in knots.
- Multiply the knots by the number of feet in a mile
Multiply the speed of the ship in knots by the number of feet in a knot, or 6076. This process uses feet, which is the common distance factor that knots and miles share.
- Divide the product by the number of feet in a mile
Divide the answer from the previous step by the number of feet in a mile, which is 5280, in order to calculate the speed of the ship in miles per hour.