Updated November 2026 · free, works in your browser
Show the formula
Time (h) = distance ÷ average speed, with both in the same system (nm and knots, km and km/h, or miles and mph).
Total time = time × (1 + margin ÷ 100).
ETA = departure + total time.
1 knot = 1 nautical mile per hour; 1 nm = 1.852 km = 1.15078 mi.
To work out a passage time, divide the distance by your average speed: 60 nautical miles at 6 knots takes 10 hours. Enter the distance, your realistic average speed and a departure time above, and the calculator gives you the duration and the estimated time of arrival (ETA).
How to use
- Choose your units: nautical miles with knots, kilometres with km/h, or statute miles with mph.
- Type the leg distance, measured on the chart from waypoint to waypoint.
- Enter the average speed you expect to make over the ground, not the top speed of the boat.
- In the full version, set the departure time and an optional safety margin in percent to allow for light winds, adverse current or a slow start.
- Read the duration, the arrival time and the total hours. The link button saves your inputs in the address so you can share the plan.
How it is calculated
The calculation is the basic relation between distance, speed and time:
Time = Distance ÷ Speed
Total time = Time × (1 + Margin ÷ 100), and ETA = Departure + Total time.
- Distance is the length of the leg in the unit you selected.
- Speed is your average speed over the ground in the matching unit. One knot is one nautical mile per hour.
- Margin is an optional percentage added on top of the calculated time.
The standard definitions apply: one nautical mile is exactly 1,852 metres (the international nautical mile), and one statute mile is 1,609.344 metres. Distances in kilometres or miles are converted to nautical miles for the extra result panel. Times are rounded to the nearest minute, and the ETA is shown in the local time of your device.
Example: a 60 nm leg at different speeds
| Average speed | Time for 60 nm |
|---|---|
| 4 knots | 15 h 0 min |
| 5 knots | 12 h 0 min |
| 6 knots | 10 h 0 min |
| 7 knots | 8 h 34 min |
| 8 knots | 7 h 30 min |
FAQ
What speed should I use for a sailing passage?
Use the average speed over the ground you can realistically hold for the whole leg. It is usually lower than the speed you see in good conditions, because wind shifts, tacking, tide and sail changes all slow you down.
How do tides and currents change the result?
A current that runs with you adds to your speed over the ground, and one against you subtracts from it. For a long leg, split the passage into sections with different average speeds, or add a safety margin to the total.
How many knots is a kilometre per hour?
One knot equals 1.852 km/h, so 10 knots is 18.52 km/h. You can also select the metric units and enter everything in kilometres and km/h.
Can I use this for a motorboat?
Yes. The formula is the same for any vessel. Enter your cruising speed and the distance, and keep in mind that fuel planning is a separate calculation.
Is this enough for safe navigation?
No. It is a planning estimate only. Always check the weather, tides and official charts, and keep a margin for the unexpected before you set out.
From passage plan to itinerary
Once you know how long each leg takes, it is easier to build a whole trip: how many hours of sailing per day feel comfortable, where you can arrive before dark, and which harbour or island makes a sensible overnight stop. Planning the nights ashore along a route, including where to stay near each stop, turns a list of legs into a relaxed itinerary.
Other tools
- Beaufort Scale to Knots ConverterTurn a Beaufort wind force into knots, km/h, mph and sea state, or find the force for any wind speed.
- Anchor Scope CalculatorEnter water depth, bow height, tide allowance and scope ratio to get the anchor rode length to let out.
- Sail Performance CalculatorCalculate displacement/length ratio, sail area/displacement ratio, capsize screening value and hull speed from a boat's dimensions.