Convert knots to mph knots ↔ miles per hour Free Online Secure
Type a value in knots and read it in miles per hour at once. The factor is exact by definition, the arithmetic happens in your browser, and nothing is sent anywhere.
Nothing uploaded
Convert to miles per hour
Common values — Convert knots to mph (knots ↔ miles per hour)
| kn | mph |
|---|---|
| 1 | 1.15077944802 |
| 2 | 2.30155889605 |
| 3 | 3.45233834407 |
| 5 | 5.75389724012 |
| 10 | 11.5077944802 |
| 20 | 23.0155889605 |
| 50 | 57.5389724012 |
| 100 | 115.077944802 |
Where these units come from
Speed has no unit of its own: it is a length divided by a time, so every trade simply kept the length it was already using. That is why the same motion is 100 km/h on a European road sign, 62 mph on an American one and 27.8 m/s in a physics problem. The knot is the oldest of them and the most literal: sailors paid out a line with knots tied at even spacing and counted how many ran through their fingers while a sand glass emptied, so the speed was read off in knots. One knot is one nautical mile per hour, and a nautical mile is a minute of latitude — which is why ships and aircraft still use it. The speed of light is the odd one out: since 1983 it is not measured but fixed at exactly 299,792,458 m/s, because the metre is now defined from it.
Where you meet them
Kilometres and miles per hour live on speedometers and road signs, metres per second in physics, engineering and wind reports, feet per second in ballistics and in American machine shops. Knots carry shipping, aviation and marine weather, and Mach numbers appear wherever an aircraft is fast enough for the air's own stiffness to matter. The speed of light turns up less in daily life than in distances: a light year is simply how far it gets in one.
Questions people ask
Is Mach 1 a fixed speed?
No. Mach is a ratio to the speed of sound in the surrounding air, and sound travels more slowly in colder air. This page uses the standard sea-level figure, 340.294 m/s, so Mach 1 here is about 1225 km/h. At the altitude airliners cruise at, the air is some 50 degrees colder and the same Mach 1 is roughly a tenth slower. An aircraft can therefore hold a constant Mach number while its speed over the ground changes.
Why do ships and aircraft use knots rather than km/h?
Because a nautical mile is one minute of arc of latitude. A vessel making one knot covers one minute of latitude in an hour, so speed, time and position on a chart fit together without conversion. The same reasoning kept the nautical mile at exactly 1852 metres rather than rounding it to something tidier.
Is the answer exact?
Where both units are defined in terms of one another by whole numbers, yes — the page says so above the figure, and the only rounding is in how many digits are shown. Where the ratio has no finite decimal, the page shows twelve significant digits and says the relation is approximate rather than pretending otherwise.
Does anything I type leave my device?
No. The arithmetic runs in your browser; nothing is uploaded and there is no server to upload it to. Load the page once and it keeps working with the network switched off.
Hurricane advisories and marine forecasts: from knots to mph
When a storm threatens the Gulf coast, the National Hurricane Center publishes its advisories with the maximum sustained wind in both miles per hour and knots, and marine forecasts for boaters speak only in knots. Newspapers and television use mph, the radio for ships uses knots, and an official warning may mention one while the page you are reading shows the other. To convert knots to mph, multiply by 1.1508: 64 knots is 73.6 mph, 100 knots is 115.1 mph and 137 knots is 157.7 mph. The calculator above multiplies as you type, and the sections below show how the units line up for storms, gales, small-craft advisories and everyday boating.
You will find the rule with worked examples, a short profile of each unit, a comparison, a long set of cases from weather and the sea and the slips to avoid. The arithmetic runs in your browser, and what you type is not sent anywhere. In a storm, follow the instructions of the authorities.
How to convert knots to mph: multiply by 1.1508
The rule
A knot is a nautical mile per hour, 1,852 metres, while a statute mile is 1,609.344 metres. The ratio is 1.1508. To convert knots to mph, multiply the knots by 1.1508. So 20 knots is 23.0 mph, 50 knots is 57.5 mph and 85 knots is 97.8 mph. To go the other way, multiply mph by 0.869.
Worked examples
A small-craft advisory wind of 25 knots is 28.8 mph. A tropical storm of 50 knots is 57.5 mph. A category 3 hurricane of 100 knots is 115.1 mph, and a category 5 of 140 knots is 161.1 mph.
Why 1.1508
The two miles differ by about 15 per cent. At low speeds the gap is small, but at hurricane speeds it is 15 to 20 mph, enough to change a category. Treating knots as mph would understate a 110-knot storm, which is 126.6 mph, by 16 mph.
A quick sanity test
The mph figure is always 15 per cent bigger than the figure in knots. If a “convert knots to mph” calculation result is smaller than the input, you used 0.869 by mistake.
The knot
The unit of marine and aviation weather
The knot is the standard unit for wind in marine forecasts, aviation reports and many meteorological products. The National Weather Service issues marine warnings in knots, and hurricane products list knots alongside mph and km/h.
Where it appears
Marine forecasts, buoy reports, aviation weather and hurricane advisories.
The mile per hour
The unit of public weather
The mile per hour is the unit in which the American public hears about wind. Television forecasts, news reports and local warnings speak in mph, and the categories of the Saffir-Simpson scale are defined in it.
Where it appears
Television weather, local warnings, newspapers and the Saffir-Simpson scale.
The two units compared
A knot is 1.151 mph, so the mph number runs 15 per cent higher. A storm with 100-knot winds is a 115 mph storm. The public hears the bigger figure, the mariner reads the smaller one, and both describe the same wind. Mixing them up leads to underestimating a storm.
The factor is exact, with no rounding. The only trap is direction: from knots to mph the figure grows.
Where the conversion shows up
The Saffir-Simpson scale in knots
Category 1 covers 64 to 82 knots, which is 74 to 94 mph. Category 2 covers 83 to 95 knots, or 96 to 109 mph. Category 3 covers 96 to 112 knots, or 111 to 129 mph. Category 4 covers 113 to 136 knots, or 130 to 156 mph. Category 5 starts at 137 knots, or 158 mph. Marine products give knots, public ones mph. A “convert knots to mph” calculation moves between the two.
Tropical storms and gales
A tropical storm has sustained winds of 34 to 63 knots, which is 39 to 73 mph. A gale warning applies to winds of 34 to 47 knots, which is 39 to 54 mph, a storm warning to 48 to 63 knots, or 55 to 72 mph, and a hurricane force wind warning to 64 knots or more, or 74 mph. These are the standard thresholds in US marine forecasts.
Small-craft advisories
Small-craft advisories are issued for winds of about 20 to 33 knots, which is 23 to 38 mph, depending on the region, or for seas that are hazardous to small boats. A boater who hears "small craft advisory" and "winds 25 knots" should read it as nearly 29 mph and stay in port unless the boat and crew are equipped for it.
Reading an NHC advisory
A typical advisory reads: "Maximum sustained winds are near 100 mph (160 km/h) with higher gusts." Marine products from the same office give 85 knots. The three numbers 100 mph, 160 km/h and 85 knots are the same wind. When only one is given, you can work out the others with the factors 1.609 and 0.869. Practising on a few advisories makes the unit change automatic.
Coastal flooding and evacuation
Evacuation orders are linked to category and surge. A category 3 storm, 100 knots or 115 mph, usually triggers mandatory evacuation of low-lying coasts. Local officials speak in mph, and sailors who move boats to hurricane holes speak in knots. A “convert knots to mph” calculation on the forecast wind helps you know which category applies.
Wind loads on buildings and boats
Wind force rises with the square of speed. A boat moored in 50 knots, which is 57.5 mph, feels four times the force of one in 25 knots, which is 28.8 mph. Marinas advise doubling lines and removing sails before a storm. Insurance policies also refer to named wind speeds in mph.
The Beaufort scale in mph and knots
Force 5 is 17 to 21 knots, or 20 to 24 mph. Force 7 is 28 to 33 knots, or 32 to 38 mph. Force 9 is 41 to 47 knots, or 47 to 54 mph. Force 11 is 56 to 63 knots, or 64 to 72 mph. Force 12 is 64 knots or more, or 74 mph. The scale was designed for sailors and is still used in marine forecasts across the world.
Spreadsheet formulas
Place speeds in knots in column A and use =A2*1.150779 in column B. For the reverse, use =B2*0.868976. Add a column that looks up the Saffir-Simpson category with a nested IF. Label each column with its unit and use one decimal.
Rounding and precision
The factor is exact: 85 knots is 97.81 mph. Advisories round wind to the nearest 5 mph, so 85 knots becomes 100 mph, which is 87 knots. Knowing this explains why a reported 100 mph can match both 85 and 87 knots. Do not read false precision into rounded figures.
A mental shortcut
Add 15 per cent. For 20 knots: 3 more gives 23 mph. For 60 knots: 9 more gives 69 mph. For 100 knots: 15 more gives 115 mph. The error is under 0.1 per cent, because 1.15 is very close to 1.1508.
Landmarks to memorise
34 knots is 39 mph, the start of a tropical storm. 64 knots is 74 mph, the start of a hurricane. 96 knots is 111 mph, a major hurricane. 137 knots is 158 mph, category 5. With these landmarks you can place any forecast on the scale.
Reference ladder
10 knots is 11.5 mph. 20 knots is 23 mph. 30 knots is 34.5 mph. 40 knots is 46 mph. 50 knots is 57.5 mph. 70 knots is 80.6 mph. 90 knots is 103.6 mph. 120 knots is 138.1 mph. 150 knots is 172.6 mph. A ladder like this makes a quick check easy.
Checking by reversing
To check any convert knots to mph result, multiply it by 0.869. If 100 knots became 115.1 mph, then 115.1 times 0.869 is 100. A second test is the size: the mph number is 15 per cent bigger.
Relation to km/h and m/s
One knot is 1.852 km/h and 0.514 m/s. A storm of 100 knots is 185 km/h and 51.4 m/s. Foreign reports give km/h or m/s. A reader who knows these factors can follow a storm that crosses several countries and appears in different units in each.
Intensity changes
Forecasters say a storm will strengthen from 70 knots to 100 knots in 24 hours, which is 80.6 to 115.1 mph, an increase of 35 mph, called rapid intensification when it reaches 30 knots, or 34.5 mph, in a day. The definition is in knots, and the headlines in mph. A change of 30 knots equals a jump of about one and a half categories.
Planning a day on the water
Check the marine forecast for the afternoon, not only the morning. A forecast of 10 to 15 knots, which is 11.5 to 17 mph, is pleasant, while 15 to 20 knots, which is 17 to 23 mph, is brisk. If the forecast calls for gusts to 25 knots, or 29 mph, think about reefing or staying close to shore. A “convert knots to mph” calculation on each number makes the forecast concrete.
Communicating with relatives ashore
Sailors who cruise far from home send updates to relatives. "Winds 30 knots" means little to someone who thinks in mph; "35 mph" conveys more. Many cruisers include both: "30 knots (35 mph)". The practice avoids needless worry and shows good seamanship, since the skipper evidently has the situation measured.
Radar speeds and ship tracking
Ship-tracking websites show vessel speed in knots. A cargo ship making 14 knots is doing 16.1 mph, and a ferry making 20 knots is at 23 mph. Visitors can compare these with road speeds, and it is striking how slow a large ship is. Yet its momentum is huge, which is why stopping takes miles.
A worked example
An advisory states: "Maximum sustained winds 90 knots, gusts 110 knots." In mph that is 103.6 and 126.6. The storm is a category 2, close to category 3, which starts at 96 knots, or 111 mph. Gusts at 126.6 mph could damage roofs. A boat owner who reads the advisory in knots reaches the same conclusion by recognising the categories.
Fishing fleets and weather windows
Commercial fishermen watch weather windows closely. A boat that steams at 12 knots, which is 13.8 mph, to grounds 90 nautical miles away needs 7.5 hours. A forecast of 30 knots, or 34.5 mph, rising in the evening can force a boat to stay in port. Skippers talk in knots, and families listening on the news hear mph. A “convert knots to mph” calculation bridges the two for people who wait on shore.
Sea-state descriptions
Marine forecasts describe the sea as smooth, slight, moderate, rough, very rough or high. A wind of 20 knots, which is 23 mph, over a day builds a moderate to rough sea. At 35 knots, or 40 mph, the sea becomes very rough to high. Charts and apps give both the wind speed and the expected wave height, and a boater uses them together to decide.
Gusts and sustained winds
Gusts are 20 to 40 per cent above sustained winds. A storm with sustained winds of 80 knots, which is 92 mph, can have gusts of 100 knots, which is 115 mph. Damage depends on gusts, while the category depends on sustained winds. Warnings state both, and the units must match in your mind to avoid underestimating the danger.
Averaging time
The US reports sustained winds averaged over one minute, while many other countries use ten minutes. A one-minute average of 100 knots is roughly a ten-minute average of 93 knots. In mph that is 115 against 107. Comparing a US hurricane with a typhoon reported elsewhere requires care with both the unit and the averaging time, and a “convert knots to mph” calculation fixes only the unit.
Buoy reports
Offshore buoys report wind in knots and wave height in feet or metres. A reading of 30 knots with gusts to 40 is 34.5 mph with gusts to 46 mph. Fishermen and sailors check buoys before leaving port, and the numbers are often posted on harbour boards in both units for visitors.
Storm surge and waves
The height of the sea in a storm depends on the wind speed, the time it blows and the distance over open water. A sustained wind of 40 knots, which is 46 mph, can build seas of 4 to 6 metres, or 13 to 20 feet, in open water. A storm of 100 knots drives much higher waves and a surge at the coast. The numbers rise with the square of wind speed.
Aviation weather
Pilots get wind in knots from METARs. "Wind 270 at 15 gusting 25" means 17 mph with gusts to 29 mph. The crosswind limit for a small plane may be 15 knots, which is 17 mph, and for an airliner 33 knots, which is 38 mph. A passenger who sees a sign saying "strong winds" at an airport can estimate what is meant with a “convert knots to mph” calculation.
Sailing and wind strength
Sailors reef a small keelboat at 18 to 20 knots, which is 21 to 23 mph, and stay ashore in 30 knots, which is 34.5 mph. Racers can handle 25 knots, or 29 mph, with the right sails. A force 6 on the Beaufort scale is 22 to 27 knots, or 25 to 31 mph, and force 8 is 34 to 40 knots, or 39 to 46 mph. The scale is in knots on the water and mph in popular guides.
Great Lakes forecasts
On the Great Lakes, forecasts are in knots for ships and in mph for the public. A gale warning of 35 knots, which is 40 mph, can produce 5-metre waves, or 16 feet, on Lake Superior. The famous November gales that sank freighters had winds of 50 to 70 knots, which is 58 to 81 mph. Mariners know the numbers well.
More values for convert knots to mph
A longer list of conversions
If the value you need is not in the first list, these further conversions may be close enough to read off directly:
- 0.1 kn = 0.115078 mph
- 0.5 kn = 0.57539 mph
- 3 kn = 3.45234 mph
- 4 kn = 4.60312 mph
- 7 kn = 8.05546 mph
- 15 kn = 17.2617 mph
- 20 kn = 23.0156 mph
- 75 kn = 86.3085 mph
- 200 kn = 230.156 mph
- 500 kn = 575.39 mph
- 2,000 kn = 2,301.56 mph
- 10,000 kn = 11,507.8 mph
Common slips when you convert knots to mph
Treating knots as mph
A knot is 1.151 mph. A 100-knot wind is 115 mph, not 100, and the gap matters at hurricane strength.
Dividing instead of multiplying
From knots to mph the number grows. If 100 knots became 87, you divided.
Mixing averaging times
One-minute and ten-minute winds are different measures. Convert the unit, but compare like with like.
Quick questions
What is the method for a “convert knots to mph” calculation?
Multiply the knots by 1.1508.
What is 100 knots in miles per hour?
115.1 mph.
What is 64 knots in miles per hour?
73.6 mph.
What is 1 mph in knots?
0.869 knots.
Is my figure stored or sent?
No, it stays on your device.
Where to go next
Other speed tools are listed here: Convert knots to km/h, Convert knots to m/s, Convert km/h to mph, Convert ft/s to mph, Convert mph to Mach, Convert km to mi, Convert mi to km, Convert °C to °F, Convert °F to °C. For the opposite direction, use Convert mph to knots.
The takeaway: a “convert knots to mph” calculation multiplies by 1.1508 and labels the result mph. The figure you enter is processed on your device only.