MPH to Knots Converter
Unit ConversionConvert miles per hour to knots using the exact nautical-mile-based factor.
Knots
Equivalent speed in knots
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SponsoredThis calculator converts a speed in miles per hour to knots using the exact factor derived from the international nautical mile: divide the mph value by 1.150779448. A knot is one nautical mile per hour, and since a nautical mile is defined as exactly 1,852 meters, this conversion has a precise, unchanging ratio rather than an approximation.
Sailors, pilots, and meteorologists work in knots by default, so this conversion comes up whenever a road-speed mph figure, a wind forecast in mph, or a boat's GPS reading needs to be translated into the nautical unit used for navigation and official reports. Since a nautical mile is longer than a statute mile, one mph is always slower than one knot, which is why the mph number converts down.
For the reverse direction, converting knots back into mph, or converting mph into kilometers per hour or meters per second instead, see the related converters below.
MPH to Knots conversion table
This table covers common wind-speed and boat-speed reference points.
| Miles per Hour | Knots |
|---|---|
| 0 mph | 0 kn |
| 10 mph | 8.69 kn |
| 20 mph | 17.38 kn |
| 25 mph | 21.72 kn |
| 30 mph | 26.07 kn |
| 40 mph | 34.76 kn |
| 50 mph | 43.45 kn |
| 100 mph | 86.90 kn |
The MPH to Knots formula
To convert miles per hour to knots, divide the mph value by 1.150779448. For example, 30 mph divided by 1.150779448 equals 26.07 knots.
To go the other way, from knots back to mph, multiply by 1.150779448 instead. For example, 26.07 knots times 1.150779448 equals 30 mph. For the kilometers-per-hour or meters-per-second scale instead, use the MPH to Kilometers per Hour or MPH to Meters per Second converters below.
Why mph converts down to a smaller knot number
A statute mile, the mile used for mph, is exactly 1,609.344 meters, while a nautical mile, the mile used for knots, is exactly 1,852 meters, about 15% longer. Since a knot covers more real distance in the same hour, converting an mph value into knots always produces a smaller number, the mirror image of the knots-to-mph conversion.
When a wind or boat-speed reading is worth converting
US weather apps and car-based wind-speed estimates typically report in mph, while official marine forecasts, small-craft advisories, and aviation briefings use knots. Converting an mph figure to knots is useful for boaters and pilots cross-checking a casual mph reading against the knot-based thresholds those official warnings actually use.
Frequently Asked Questions
What is the formula to convert mph to knots?
Divide the mph value by 1.150779448. For example, 20 mph divided by 1.150779448 equals 17.38 knots.
What is 1 mph in knots?
1 mile per hour equals approximately 0.869 knots.
How fast is 50 mph in knots?
50 mph equals approximately 43.45 knots.
Is the mph to knots conversion exact?
Yes. The international nautical mile is defined as exactly 1,852 meters and the statute mile as exactly 1,609.344 meters, so the conversion factor carries no rounding error.
Why is one mph slower than one knot?
A nautical mile, the basis for knots, is about 15% longer than the statute mile used for mph. Since a knot covers more distance in the same hour, one knot is always faster than one mph.
Where would I need to convert mph to knots?
Boaters, pilots, and anyone checking a casual mph wind or GPS reading against official marine or aviation reports, which are given in knots, would need this conversion.
Can an mph-to-knots result be negative?
No. Speed is a non-negative magnitude in this context, so this calculator floors its result at 0 knots for an mph value of 0 or below.
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