How fast is a knot? One knot is one nautical mile per hour, so it equals exactly 1.852 km/h by definition. In US units, that is about 1.15 mph, or roughly 1.69 feet per second. In SI units, one knot is about 0.514 meters per second. As a result, 10 knots is about 11.5 mph.
How Fast Is a Knot? Convert Your Own Speed
First, enter any speed below and pick the unit you have. The converter then uses the exact definition of the nautical mile (1,852 meters) and shows the result in miles per hour, kilometers per hour, meters per second and feet per second.
First of all, a knot is a unit of speed, not distance. In short, it tells you how many nautical miles a ship or aircraft covers in one hour. Because a nautical mile is longer than a land mile, a knot is a little faster than one mile per hour.
You meet knots on boat speedometers, marine weather forecasts, aviation charts and hurricane reports. For example, a pilot reports airspeed in knots, and a harbor sign may set a 5-knot limit. Meanwhile, the people on shore usually think in mph or km/h, so a quick conversion helps.
Above all, the value itself is fixed. According to NOAA’s National Ocean Service, a knot is one nautical mile per hour, or roughly 1.15 statute miles per hour. In addition, the nautical mile has been set at exactly 1,852 meters since an international agreement in 1929, and the United States adopted that value in 1954. The NIST Guide to the SI lists the same factors: 1,852 m per nautical mile and about 0.5144 m/s per knot.
Knots to mph and km/h Chart
Overall, this chart covers the speeds that come up most often on the water and in the air. Also, every value comes from the exact definition and is rounded to two decimals.
| Knots | Miles per hour | Kilometers per hour | Meters per second |
|---|---|---|---|
| 1 kn | 1.15 mph | 1.85 km/h | 0.51 m/s |
| 2 kn | 2.30 mph | 3.70 km/h | 1.03 m/s |
| 5 kn | 5.75 mph | 9.26 km/h | 2.57 m/s |
| 10 kn | 11.51 mph | 18.52 km/h | 5.14 m/s |
| 15 kn | 17.26 mph | 27.78 km/h | 7.72 m/s |
| 20 kn | 23.02 mph | 37.04 km/h | 10.29 m/s |
| 25 kn | 28.77 mph | 46.30 km/h | 12.86 m/s |
| 30 kn | 34.52 mph | 55.56 km/h | 15.43 m/s |
| 40 kn | 46.03 mph | 74.08 km/h | 20.58 m/s |
| 50 kn | 57.54 mph | 92.60 km/h | 25.72 m/s |
| 100 kn | 115.08 mph | 185.20 km/h | 51.44 m/s |
| 250 kn | 287.69 mph | 463.00 km/h | 128.61 m/s |
| 500 kn | 575.39 mph | 926.00 km/h | 257.22 m/s |
Printable tip: save or print this chart and tape it near the helm. Going the other way, 1 mph is about 0.87 knots and 1 km/h is about 0.54 knots.
Recommended Tools for Measuring Speed in Knots
Most modern boats read speed from GPS, so a handheld GPS unit is the simplest way to see knots directly. In addition, a pocket wind meter shows wind speed in knots, which sailors and drone pilots both use. Finally, a pair of chart dividers lets you measure nautical miles on a paper chart, so you can work out speed from distance and time. These picks are based on manufacturer specs and buyer reports.
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How Fast Is a Knot Compared With mph and km/h?
The confusion usually starts with the word “mile”. In fact, there are two different miles, and a knot uses the longer one. So the same number means a different speed depending on the unit.
| Unit | Based on | Exact size | Where you see it |
|---|---|---|---|
| Knot (kn, kt) | Nautical mile per hour | 1,852 m per hour = 1.852 km/h | Ships, aircraft, marine and aviation weather |
| Mile per hour (mph) | Statute (land) mile per hour | 1,609.344 m per hour | US and UK roads |
| Kilometer per hour (km/h) | 1,000 m per hour | 1,000 m per hour | Roads in most countries |
| Meter per second (m/s) | SI base units | 3.6 km/h | Science, engineering, wind data |
A nautical mile is about 6,076 feet, while a land mile is 5,280 feet. Therefore, one nautical mile is about 1.151 land miles, and that same ratio turns knots into mph.
How to Convert Knots by Hand
Of course, the converter above does this for you. Still, the math is short enough to do in your head on deck.
- Write down the speed in knots. For example, take 18 knots from the boat’s GPS.
- For mph, multiply by 1.151. Thus 18 x 1.151 = about 20.7 mph. For a rough answer, add 15 percent.
- For km/h, multiply by 1.852. Here 18 x 1.852 = 33.3 km/h. A quick estimate is “double it, then subtract 7 percent”.
- For meters per second, divide by 1.944. So 18 / 1.944 = about 9.3 m/s, or roughly half the knot value.
- Going back to knots, reverse the step. Divide mph by 1.151, or divide km/h by 1.852.
- Round only at the end. Keep three decimals in the factor, then round the final answer to one decimal.
Where the Word Knot Comes From
In fact, the name is literal. From around the 1600s, sailors measured speed with a “common log”, also called a chip log: a flat, weighted wooden board tied to a long line. Indeed, NOAA describes the line as having knots tied at regular intervals.
A sailor threw the board over the stern, where it stayed roughly still in the water. Next, the line ran out as the ship moved away. Meanwhile, a second sailor turned a small sandglass. When the sand ran out, they stopped the line and counted how many knots had passed. Finally, that count was the speed.
The spacing made the math work. For instance, if you rebuilt a chip log today with a 28-second sandglass, the knots would need to be about 47 feet 3 inches (14.4 m) apart. In other words, that is 1,852 m x 28 / 3,600 seconds. Historic logs used different spacings, because the nautical mile itself was not standardized until the 20th century. So the old readings were estimates, not exact values.
You may read that the knot dates back to ancient times. In fact, the log-line method belongs to the age of sail, and the exact modern value is less than a hundred years old.
How Fast Is a Knot in Real-World Terms?
At first, one knot sounds like a slow stroll. However, multiply it and things get fast. For instance, the table below gives a feel for common speeds; the vessel and aircraft figures are typical ranges, not fixed values.
| Example | Typical speed in knots | About in mph |
|---|---|---|
| No-wake zone limit (many harbors) | 5 kn | 6 mph |
| Cruising sailboat | 5 to 8 kn | 6 to 9 mph |
| Category 1 hurricane threshold | 64 kn | 74 mph |
| Commercial jet at cruise (true airspeed) | roughly 450 to 500 kn | roughly 520 to 575 mph |
The hurricane row comes from the National Hurricane Center’s Saffir-Simpson scale, which lists Category 1 as 64 to 82 knots. For aircraft, our guide to how fast planes fly breaks speeds down by aircraft type. Similarly, marine animals are often clocked in knots; see how fast whales can swim for those numbers.
Why Ships and Planes Still Use Knots
Knots survive because they match the map. A nautical mile is based on one minute of latitude, so 60 nautical miles equal one degree of latitude. As a result, a navigator can read distance straight off the latitude scale on the side of a chart.
Consequently, planning is simple. For example, if a port is 100 nautical miles away and you make 20 knots, you arrive in 5 hours. Also, aviation uses the same charts and the same math, so pilots and air traffic controllers report speeds in knots worldwide. For a deeper history, read why ships measure speed in knots.
Do and Don’t When Working With Knots
Do
- Check which unit your GPS or speedometer shows.
- Pair knots with nautical miles on charts.
- Round only after the full calculation.
- Note whether a plane’s speed is airspeed or ground speed.
- Write “kn” or “kt” clearly in logbooks.
Don’t
- Say “knots per hour”.
- Treat knots and mph as the same number.
- Assume old chip-log speeds were exact.
- Plan fuel with mixed units.
- Forget that currents change your speed over ground.
Honest Limits of Speed Readings
The definition of a knot is exact, but most speed readings are not. First, GPS shows speed over ground, which includes the push of tides and currents. For example, a boat moving through the water at 6 knots against a 2-knot current makes only about 4 knots over ground. Second, a paddlewheel speed log measures speed through the water, so it can read high or low if weed fouls the wheel. Also, aircraft have several speeds: indicated airspeed, true airspeed and ground speed can differ by many knots at altitude. In short, the conversion on this page is precise; the number you feed into it is only as good as the instrument.
When Accuracy Really Matters
For casual boating, 1 knot = 1.15 mph is close enough. Nevertheless, a few situations call for the full factor and a careful reading:
- Passage and fuel planning. Small errors add up over long distances, so carry three decimals.
- Speed limits in harbors and channels. Posted limits are often in knots, and fines can follow if you guess.
- Weather decisions. Marine forecasts give wind in knots; converting wrongly can make a gale sound milder than it is.
Frequently Asked Questions
How fast is a knot in mph?
One knot is about 1.15 mph (1.1508 mph to four decimals). So 20 knots is about 23 mph.
How fast is a knot in km/h?
One knot is exactly 1.852 km/h, because a nautical mile is defined as exactly 1,852 meters.
How fast is a knot in meters per second?
One knot is about 0.514 m/s. Conversely, 1 m/s is about 1.94 knots.
How fast is a knot in feet per second?
One knot is about 1.69 feet per second, since a nautical mile is about 6,076 feet.
Is a knot faster than a mile per hour?
Yes. A knot is about 15 percent faster than 1 mph because a nautical mile is longer than a land mile.
Why is it called a knot?
Sailors once measured speed by counting the knots on a log line that ran out behind the ship during a timed interval.
What does “kt” or “kn” mean?
Both are abbreviations for knot. Aviation often uses kt, while kn is common in science and marine writing.
How many mph is 30 knots?
Likewise, 30 knots is about 34.5 mph, or 55.6 km/h.
Do airplanes use knots?
Yes. In fact, pilots and air traffic control report airspeed and wind speed in knots almost everywhere in the world.
Is “knots per hour” correct?
No. A knot already means one nautical mile per hour, so you simply say a boat is going 10 knots.
How Fast Is a Knot: The Bottom Line
To sum up, one knot is one nautical mile per hour: exactly 1.852 km/h, about 1.15 mph and about 0.514 m/s. Also, the name comes from the knotted log lines of the age of sail, and the unit lasts because it lines up with latitude on every nautical chart.
Finally, for any other value, use the converter at the top of the page. However, remember that the reading from your GPS, speed log or airspeed indicator is the part that can be wrong, not the conversion.
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