Speed Made Good Calculator
Speed made good is the real average speed you achieve between two fixes, distance traveled divided by the time it took. Because it folds in the effect of current and steering, it is the speed that actually governs your arrival time, not the speed through the water shown on a log. Enter the distance run in nautical miles and the time taken in hours and minutes, then add a distance still to run, and this calculator returns your speed made good in knots along with the time remaining to the next point.
Speed made good formula
Time (hours) = hours + minutes / 60
Speed made good = distance / time (hours)
Time to run = distance still to run / speed made good
Speed in mph = knots x 1.15078
Distance in nautical miles divided by elapsed time in decimal hours gives speed made good in knots. Dividing the remaining distance by that speed gives the time still to run, shown both in decimal hours and as hours and minutes.
Speed made good notes
- Speed made good is over the ground, so it already includes current effects.
- Use consistent units: nautical miles with knots, or convert first.
- One nautical mile is one minute of latitude, about 1,852 meters.
- The remaining time assumes the same speed made good continues.
- Re-check at each fix as current and conditions change.
Speed made good: frequently asked questions
What is speed made good?
Speed made good (SMG) is the actual average speed achieved over the ground between two points, found by dividing the distance traveled by the time taken. Unlike speed through the water, it includes the effect of current and steering, so it is the figure that matters for arrival times.
How is speed made good calculated?
Speed made good in knots equals distance in nautical miles divided by time in hours. If time is given in hours and minutes, convert minutes to a fraction of an hour first: hours + minutes/60. So SMG = distance / (hours + minutes/60).
What is the difference between speed made good and speed over ground?
Speed over ground is the instantaneous ground speed at a moment, typically from GPS. Speed made good is the average ground speed over a passage between two fixes. Over a steady leg with no maneuvering, the two converge, but SMG smooths out short-term variation.
How do I estimate time of arrival from speed made good?
Divide the remaining distance by your speed made good to get the remaining time in hours, then add it to the current time. This calculator returns the remaining time and a clock-style hours-and-minutes breakdown for a distance still to run that you enter.
Why use nautical miles and knots?
A nautical mile is one minute of latitude, about 1,852 meters, which makes chart work straightforward. A knot is one nautical mile per hour. Using these units keeps distance, speed, and time consistent in marine navigation. Convert from statute miles by dividing by 1.15078.
Official sources
- U.S. Coast Guard Navigation Center: Navigation Center.
- NOAA Office of Coast Survey: Nautical Charts.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.