Convert Miles per Hour to Knots
Miles per hour to knots is the conversion pilots, sailors, and weather watchers reach for when a ground speed in mph needs to be read on an aviation or marine instrument. One mph is about 0.868976 knots, so the number always gets a little smaller when you switch from mph to knots.
Miles per hour to Knots conversion table
| Miles per hour (mph) | Knots (kn) |
|---|---|
| 1 | 0.868976 |
| 2 | 1.737952 |
| 3 | 2.606929 |
| 5 | 4.344881 |
| 10 | 8.689762 |
| 20 | 17.379525 |
| 50 | 43.448812 |
| 100 | 86.897624 |
| 500 | 434.488121 |
| 1,000 | 868.976242 |
The formula
To convert miles per hour to knots, multiply the speed in mph by 0.868976:
knots = miles per hour × 0.868976
A worked example
Say a small plane is cruising at 150 mph and the pilot needs that speed in knots for the cockpit instruments:
150 × 0.868976 = 130.35 knots
That's the kind of conversion pilots do constantly, since airspeed indicators are marked in knots while everyday speed intuition is often built around mph.
Why it's an approximation
A knot is one nautical mile per hour, and a nautical mile (1.852 km) is a different length than the standard mile (1.609344 km) — they come from entirely separate definitions, one tied to a minute of latitude on the globe, the other to a fixed metric length. Dividing one by the other produces a decimal that doesn't terminate cleanly, so 0.868976 is that ratio rounded to six decimal places — precise enough for any practical use, but technically a rounded figure.
When you'll use it
Reading aviation weather reports and airspeed instruments, converting boat and wind speeds for sailing, and comparing marine forecasts that report wind in knots against everyday mph intuition.
Frequently asked questions
How many knots are in a mile per hour?
About 0.868976 knots. It's a very close, well-established value, but it's a rounded decimal rather than an exact whole-number relationship.
Is the mph to knots conversion exact?
No, it's an approximation. A knot is based on the nautical mile, which is a different length than the standard mile, so the ratio between them doesn't come out to a clean, terminating number — 0.868976 is that ratio rounded to six decimal places.
What's a quick way to estimate mph to knots in my head?
Cut the mph value by about 13%. A 100 mph wind is close to 87 knots; a 20 mph breeze is close to 17 knots. For anything that matters, use the factor above.