Speed in Knots
One knot is one nautical mile per hour.
Formula
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Example
30 nm in 4 h: v = 7.5 knots
How it works
This formula finds speed by dividing how far a vessel has travelled by how long it took. In nautical contexts, the distance is measured in nautical miles and the time in hours, so the answer comes out in knots, which is the standard unit of boat and ship speed. It works because speed is defined as distance per unit time: if a ship covers more nautical miles in the same time, its speed is higher.
When to use it
Use this when you know a boat’s travel distance and the time taken, and you need its average speed in knots. It is common in sailing, shipping, navigation, and voyage planning.
Worked example, step by step
A ferry travels 54 nautical miles in 6 hours. Use the formula: v = d / t Substitute the values: v = 54 / 6 Calculate: v = 9 Final answer: the ferry’s average speed is 9 knots.
Common mistakes to avoid
- Using statute miles instead of nautical miles
- Dividing time by distance instead of distance by time
- Forgetting that the result is an average speed over the whole trip
Did You Know?
'Knots' comes from sailors counting knots on a rope paid out behind the ship over a timed interval.
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