Calculating Estimated Time of Arrival (ETA)

TIME, DISTANCE AND SPEED

Understanding how to calculate Time, Distance and Speed is a key and essential skill for safe navigation. In order to calculate how much time it will take you to reach your destination we must use the following formula: Time (In minutes) = Distance (In nautical miles) x 60 / Speed (In knots). For example: If you are travelling 20 nautical miles at a speed of 5 Knots it will take you 240 minutes to complete the trip not including external factors. In order to convert this to hours divide by 60: 240/60 = 4 Hours.

1 knot is 1 nautical mile per hour. A nautical mile is slightly longer than a Land mile. One nautical mile is equal to 1.15 land miles. For land navigation if it takes a car 1 hour to travel 50 miles then the vehicle must be averaging 50 mph. This concept works in the same way with a vessel for example: a ship travelling at an average speed of 10 knots will go 10 nautical miles in one hours.

  1. Distance = Speed x Time / 60
  2. Speed = Distance x 60 / Time
  3. Time = Distance x 60 / Speed

When using formulas 1 and 2 convert hours and minutes to total minutes before calculating.

  • For example: 2:45 = 165 total minutes.

1. A ship is traveling at 7 knots. How far will it travel in 30 minutes?

Distance = Speed x Time / 60 

7 x 30 / 60  =  210 / 60  =  3.5 Nautical Miles

2. A ship travels 12 nautical miles in 45 minutes. What is the speed?

Speed = Distance x 60 / Time 

12 x 60 / 45  =  720 / 45  =  16 Knots

3. A ship is travelling at 30 Knots. How long will it take to travel 45 nautical miles?

Time = Distance x 60 / Speed 

45 x 60 / 30  =  2700 / 30  =  90 Minutes