Boat Speed, Distance & Time Calculator
A free, browser-based calculator. Runs entirely in your browser — no sign up, nothing stored.
Enter Values
How to use this calculator
- Enter any two of: speed (knots), distance (nautical miles) and time (hours).
- Leave the third blank — the calculator solves for it.
- Read all three, with distance also in km and time in hours and minutes.
How it works
The Boat Speed, Distance & Time Calculator does passage-planning maths in nautical units. One knot is exactly one nautical mile per hour, which keeps the arithmetic simple.
Speed = distance ÷ time, distance = speed × time, and time = distance ÷ speed. Enter the two values you know and it returns the third.
Worked example
30 nm at 6 knots. Time = 30 ÷ 6 = 5 hours. At 6 knots you'd cover 30 nautical miles (about 55.6 km) in 5 hours.
Frequently asked questions
What is a knot?
A knot is one nautical mile per hour. A nautical mile (1.852 km) is based on one minute of latitude, which is why it's used at sea and in the air.
Is this my speed over ground or through the water?
It's whichever distance and time you put in. For an accurate ETA over the ground, allow for current and leeway, which change your actual track and speed.
Related tools
Tip: Enter any known values to calculate the remaining results.
All calculations run in your browser. Your inputs are never saved or transmitted.