What this calculator does
Turn a speed in knots into miles per hour, or mph into knots. A knot is one nautical mile per hour. Sailors, pilots, air-traffic control and marine and aviation weather forecasts all use knots. Road traffic and most US weather apps use ordinary (statute) miles per hour. You need to switch between them whenever a forecast in knots meets someone thinking in mph. It also comes up when you compare a boat's speed with a car's.
The nautical mile is exactly 1,852 meters. It was first chosen to roughly match one minute of latitude (one sixtieth of a degree north or south). That's why navigators like it: they can read distance on a chart straight off the latitude scale along the side. The statute mile is 1,609.344 m. So one knot is 1,852 ÷ 1,609.344 ≈ 1.15078 mph.
Where it's used
Why this math matters outside the classroom:
- Boating. A boat cruising at 20 knots is moving at about 23 mph.
- Gale warnings. A marine forecast of 34 knots, where gale warnings begin, is about 39 mph.
- Aviation. A small plane cruising at 120 knots covers about 138 statute miles in an hour.
- Hurricanes. Hurricane-force winds begin at 64 knots, about 74 mph.
- Nautical miles. Students see that a knot is one nautical mile, 1,852 m, per hour.
Grade level and standards: Grades 5–6; Common Core State Standards for Mathematics 6.RP.A.3.d. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.
How to use it
- Enter a speed in knots or mph.
- Choose knots to mph, or mph to knots.
- Read the result and the working. The table shows typical boat, wind and aircraft speeds for the direction you chose.
What the inputs mean
- Value to convert
- A speed in knots (for kn → mph) or in ordinary miles per hour (for mph → kn).
- Direction
- Which way to convert.
Formula and method
mph = kn × 1,852 ÷ 1,609.344 ≈ kn × 1.15077944802 kn = mph × 1,609.344 ÷ 1,852 ≈ mph × 0.868976241901
Here kn stands for knots and mph for miles per hour. Both are distances per hour, so the conversion number is just one mile's length divided by the other's. Neither 1.15078 nor its flip side (1 divided by it) ever ends as a decimal. So the calculator shows the number to 12 significant figures, meaning 12 meaningful digits. It keeps full precision behind the scenes.
There's no such thing as "knots per hour". The "per hour" is already part of the knot. Knots per hour would describe speeding up, not a speed.
Worked example
A marine forecast calls for 20-knot winds. What is that in mph?
- The conversion number, to 12 significant figures: 1 kn ≈ 1.15077944802 mph.
- 20 × 1.15077944802 = 23.0155889605.
Result: 20 knots is about 23.02 mph.
Understanding the result
Here's a quick shortcut in your head: add 15% to knots to get mph. So 20 kn becomes 23 mph, only about 0.07% low. That's far closer than any wind forecast. For mph to knots, take off 13%.
Some wind landmarks on the Beaufort scale, a standard scale of wind strength: gale force starts at 34 knots (about 39.1 mph). Hurricane force on that scale is 64 knots and above (about 73.6 mph).
A knot is also close to half a meter per second (0.5144 m/s). That's handy when you compare marine forecasts with science data in m/s.
Assumptions and limitations
- The nautical mile is the international nautical mile of exactly 1,852 m.
- The statute mile is exactly 1,609.344 m.
- Aircraft speeds come in several kinds (indicated, calibrated, true and ground speed). The conversion changes the units, not the kind of airspeed.
- The old British Admiralty knot, based on a 6,080 ft nautical mile, is slightly different. It isn't used here.
Frequently asked questions
Why do boats and planes use knots?
A nautical mile is very nearly one minute of latitude. So distances on sea and air charts can be measured with the chart's own latitude scale. Speeds in knots then fit neatly with those distances.
Is a knot faster than a mile per hour?
Yes. One knot is about 1.15 mph, so the same speed is always a smaller number in knots.
How do I convert knots to km/h?
Multiply by exactly 1.852. A 20-knot wind is 37.04 km/h. The speed converter covers this and other pairs.
How this calculator is checked
Method: International nautical mile = 1,852 m (exact); international mile = 1,609.344 m (exact); 1 kn = 1,852/1,609.344 mph. The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-18. Found a problem? Tell us.
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