Convert nmi to km nautical miles ↔ kilometres Free Online Secure
Type a value in nautical miles and read it in kilometres at once. The factor is exact by definition, the arithmetic happens in your browser, and nothing is sent anywhere.
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Common values — Convert nmi to km (nautical miles ↔ kilometres)
| nmi | km |
|---|---|
| 1 | 1.852 |
| 2 | 3.704 |
| 3 | 5.556 |
| 5 | 9.26 |
| 10 | 18.52 |
| 20 | 37.04 |
| 50 | 92.6 |
| 100 | 185.2 |
Where these units come from
The metre was first defined in 1793 as a ten-millionth of the distance from the equator to the North Pole — a definition nobody could check without surveying a quarter of the planet. It has been redefined four times since, each time to something steadier: a platinum bar, then a prototype kept in Paris, then a wavelength of krypton light, and since 1983 the distance light travels in vacuum in 1/299,792,458 of a second. The inch stopped being a separate thing in 1959, when six countries agreed to define it as exactly 25.4 mm. That agreement is why every conversion on this page between a metric and an imperial length is exact rather than measured: both sides now descend from the same definition.
Where you meet them
Millimetres are the working unit of engineering drawings and of anything made in a workshop; centimetres belong to tailoring, furniture and school rulers; metres to rooms, fabric and running tracks. Feet and inches survive in aviation altitudes worldwide, in American and British construction, and in the diagonal of every screen you have ever bought. Nautical miles are not a quaint survival — one is a minute of latitude, which is why ships and aircraft still navigate in them.
Questions people ask
Why is a nautical mile 1852 metres?
Because it was meant to equal one minute of latitude, which averages about 1852 metres along a meridian. An international conference in 1929 fixed the figure at exactly 1852 metres, and one knot is one nautical mile per hour. That link to the globe is why ships and aircraft still navigate in them.
Which countries still measure road distances in miles?
The United States and the United Kingdom, where road signs show miles, together with a handful of smaller countries such as Liberia and Myanmar. Almost everywhere else road distances are in kilometres. One kilometre is 1000 metres and about 0.621 of a mile, so a distance in miles is about five-eighths of the same distance in kilometres.
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.
When the pilot says 120 miles out: how to convert nmi to km
Aviators and mariners speak in nautical miles, while most passengers, shippers and travellers think in kilometres. An air traffic controller tells a pilot that a storm is 40 miles ahead; a captain says the harbour is 15 miles away; a news report says a ship sank 200 miles from shore. All of these distances are nautical miles, and to understand them in the unit of road signs you have to convert nmi to km. This page does it as you type: enter nautical miles and read kilometres.
The conversion factor is exactly 1.852, because the nautical mile is defined as 1,852 metres. That makes the arithmetic straightforward, but the number is not easy to carry in your head. The sections below give the rule, worked examples, short notes on the two units, a comparison, a tour of real situations and a list of the mistakes people make.
How to convert nmi to km: multiply by 1.852
The rule
One nautical mile is exactly 1.852 km. To convert nmi to km, multiply the number of nautical miles by 1.852. 1 nmi is 1.852 km, 5 nmi is 9.26 km, 10 nmi is 18.52 km, 100 nmi is 185.2 km and 1,000 nmi is 1,852 km. Fractions work in the same way: half a nautical mile is 926 m, and 0.1 nmi is 185.2 m.
Examples
An airfield that is 25 nmi away is 46.3 km distant. A ship sinking 200 nmi from the coast is 370.4 km out. A transatlantic leg of 3,000 nmi is 5,556 km. A harbour entrance 0.5 nmi wide is 926 m wide.
A quick estimate
For a mental convert nmi to km, multiply by 2 and subtract 8 per cent of the result. For 50 nmi: 100 minus 8 is 92 km, close to the exact 92.6. For 20 nmi: 40 minus 3.2 is 36.8 km against 37.04. Another way is to multiply by 1.85, which is easy: ten times 1.85 is 18.5.
Rounding
Keep the same number of significant digits as the input. A distance of 15 nmi is 28 km, not 27.78. If the nautical miles were given to the tenth, as in 15.3 nmi, give the kilometres to the tenth, 28.3 km.
The nautical mile
The sea's own unit
The nautical mile is the unit of distance on the sea and in the air. It equals 1,852 metres and was designed to match one minute of arc of latitude, so that distances can be read straight from the side of a chart. The symbol is nmi, or M in navigation. Speed is expressed in knots, one knot being one nautical mile per hour.
Why it persists
Even though most of the world uses metric, the nautical mile has survived because it is built into the way the Earth is mapped. A navigator can move a pair of dividers on the latitude scale and have the distance at once. Such a convenience is hard to give up.
The kilometre
One thousand metres
The kilometre is the unit of land distance in most countries and the one in which maps, road signs and timetables are written. A kilometre is a thousand metres, a round figure that matches the decimal logic of the metric system.
For the passenger
Passengers on a flight or a ferry usually see kilometres on their ticket and nautical miles in the crew's announcements. Understanding both lets you judge how far you really are from land.
Nautical mile and kilometre compared
A nautical mile is 1.852 km, which is 85 per cent longer than a kilometre. The number of kilometres is therefore almost twice the number of nautical miles. It is also 15 per cent longer than the statute mile, 1.609 km, which is a source of confusion.
When you write for a mixed audience, give nautical miles first for sea and air and kilometres in brackets, for example 200 nmi (370 km). The reverse order suits land readers. Never write mile alone if you mean the nautical one.
Where you will need it
Flight planning
Pilots plan distances in nautical miles and speeds in knots. An airliner flying 450 knots covers 450 nmi per hour, which is 833 km/h. A flight of 1,200 nmi is 2,222 km and takes 2 hours 40 minutes. Passengers who see a route of 2,222 km on the ticket can check the crew's figure by converting.
Weather and radar
Weather radars give the distance to a storm cell in nautical miles. A cell 60 nmi ahead is 111 km away; at a ground speed of 420 knots it is reached in 8.6 minutes. Pilots deviate around such cells by 20 nmi, 37 km, to be safe.
Shipping and canals
The Suez Canal is 104 nmi long, 193 km. The Panama Canal is 44 nmi, 82 km. A transatlantic crossing from Southampton to New York is about 3,000 nmi, 5,556 km, and takes 5 to 6 days at 22 knots.
Ocean racing
The Vendée Globe, a solo non-stop sailing race around the world, covers about 24,300 nmi, 45,000 km. Winners finish in about 74 days at an average of around 14 knots. The conversion makes the achievement more tangible: 45,000 km is more than the circumference of the Earth.
Radar, radio and range
How far can you see?
When you convert nmi to km for radar, note that marine radar has a typical range of 24 nmi, 44 km. VHF radio works at about 25 nmi, 46 km, between ships and shore stations. A lookout on a bridge 20 m above the water sees a horizon at 9 nmi, 16.7 km. Each number is more meaningful in kilometres if you are used to road distances.
Line of sight
The distance to the horizon in nautical miles is 1.17 times the square root of the height of the eye in feet, or 2.07 times the square root of the height in metres. For a height of 25 m: 10.4 nmi, 19.3 km.
History in a nutshell
From the minute to the standard
The nautical mile is rooted in the belief that the Earth is a sphere with a measurable circumference. The earliest explorers counted distances in leagues. By the 17th century, navigators had linked the mile to a minute of latitude. In 1929 an international conference fixed its length.
The modern use
Today the unit is used by the International Civil Aviation Organization and the International Maritime Organization. Although it is not an SI unit, it is accepted for use with SI.
Putting numbers in context
Human scale
A nautical mile is the length of about eighteen city blocks of 100 m, or a walk of 22 minutes at a brisk pace.
The horizon
For an observer standing on a beach, with eyes at 1.7 m, the horizon is 2.7 nmi, 5 km, away. A ship that is farther is hull down, with only its masts visible.
Long exposure: a worked example
From ship to shore
A bulk carrier reports its position as 83 nmi from the nearest port and cruising at 12 knots. The port authority wants the distance in kilometres for the agent: 83 times 1.852 is 153.7 km. At 12 knots, which is 22.2 km/h, the ship arrives in 6.9 hours. The port tells the pilot service to be ready in seven hours. This is a typical case in which a quick convert nmi to km has a practical result.
Lessons
Do the conversion once, state both units in the message and use the same figure for the whole exchange. Repeated conversions invite small differences that lead to doubts.
Reading a navigation warning
Bulletins in nautical miles
Navigational warnings broadcast by coast stations describe hazards by position and radius: a floating container adrift within 5 nmi of a given point, a military exercise in an area 30 nmi across, a buoy off station. A skipper without a chart at hand can still make sense of such a message by doing a quick convert nmi to km: 5 nmi is 9.3 km, 30 nmi is 55.6 km. Knowing the size in kilometres lets you compare the hazard with the distance to the shore that you can read off a road atlas.
Acting on the message
If the area lies on your course, convert its dimensions, plot the corners and decide whether to alter course by a few degrees or wait for the exercise to end. The same figures can be passed on to passengers in kilometres to explain the delay.
Airline timetables and distances
Why tickets show kilometres
Airlines publish the distance of a route in kilometres or miles for loyalty programmes, while the flight plan filed with air traffic control uses nautical miles. A route of 1,850 km on a ticket is the 1,000 nmi of the flight plan, an easy pair to remember. Dispatchers must convert nmi to km when they compare the two documents, because fuel is computed in nautical miles per kilogram.
A mental pair
Remember that 1,000 nmi is 1,852 km, 500 nmi is 926 km and 250 nmi is 463 km. Those three anchors let you place most figures in a sentence, and the exact value is only a keystroke away on this page.
Ports and coasts
Distances between ports
A “convert nmi to km” calculation for Constanța to the Bosphorus gives a sea passage of roughly 180 nmi, about 333 km. Rotterdam to Hamburg is about 270 nmi, 500 km. Piraeus to Valletta is about 570 nmi, 1,056 km. Shipping tables give port-to-port distances in nautical miles.
Coastlines
The length of a coastline depends on the scale at which it is measured. National statistics usually give kilometres. A navigator will, however, use nautical miles to compare it with sailing distances.
Long ocean passages
Crossing oceans
An Atlantic crossing from Lisbon to the Caribbean is about 2,800 nmi, 5,186 km. A Pacific passage from California to Hawaii is about 2,200 nmi, 4,074 km. Small yachts take 3 to 4 weeks for these passages, averaging around 100 to 120 nmi a day.
Daily run
A daily run of 120 nmi is 222 km a day, 9.3 km/h. That is the speed of a cyclist on a relaxed ride, but sustained continuously, night and day, for weeks.
Aviation numbers
Cruising and range
Short-haul jets have a range of about 3,000 nmi, 5,556 km; long-haul jets 8,000 nmi, 14,816 km. A small private plane flies 500 nmi, 926 km, without refuelling. The numbers give a first idea of what a particular aircraft can do.
Runway and approach
An instrument approach starts about 10 nmi, 18.5 km, from the runway. A normal descent path loses 300 ft per nautical mile, so from 3,000 ft at 10 nmi the aircraft reaches the runway.
Rescue and territorial claims
Distances at stake
A search and rescue region might extend 500 nmi, 926 km, from a coast station. The maritime zones are 12 nmi (22.2 km) for territorial waters, 24 nmi (44.4 km) for the contiguous zone and 200 nmi (370.4 km) for the economic zone. These are the numbers repeated in news stories.
Why the unit matters
If a source says a vessel was 250 miles away, the nautical interpretation puts it at 463 km, the statute one at 402 km. Make sure you know which is meant.
Sailing speeds and times
Knots and kilometres per hour
A speed of 1 knot is 1.852 km/h, 10 knots 18.52 km/h, 20 knots 37.04 km/h, 30 knots 55.56 km/h. A race yacht at 12 knots does 22.2 km/h. A cruise ship at 22 knots does 40.7 km/h.
Time to arrival
Distance in nautical miles divided by the speed in knots gives the time in hours. 85 nmi at 6 knots is 14.2 hours. The same job in kilometres is 157.4 km divided by 11.1 km/h, which gives the same answer but is clumsier.
Spreadsheet formulas
Formula
To convert nmi to km for a column, enter nautical miles in column A and =A2*1.852 in column B. Format with one decimal. To convert a column of knots to km/h, use the same formula. For the reverse, divide.
Testing
Enter 1 and check that you get 1.852. Enter 100 for 185.2. If you get 160.9, the sheet uses the statute mile factor 1.609.
Statute versus nautical
Two miles
The statute mile is 1,609.344 m and the nautical mile is 1,852 m. The ratio is 1.1508. A ship's speed of 20 knots is 23 mph, not 20 mph. The difference matters when comparing sea speeds with road speeds.
How to avoid confusion
Use nmi or NM for nautical miles and mi for statute miles. In reading a text, check whether it comes from a marine or an aviation source. If so, it uses nautical miles.
Teaching the conversion
Latitude and kilometres
Have students pick two points on the same meridian on a globe, for instance 44 and 52 degrees north, and measure the difference in degrees. Each degree is 60 nmi, 111 km. The difference of 8 degrees gives 480 nmi, 889 km.
Estimation
Ask students to estimate the nautical distance across the Black Sea at its widest, 580 km, using the shortcut of halving. The answer, 313 nmi, appears after one step of dividing by 1.852.
More values for convert nmi to km
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 nmi = 0.1852 km
- 0.5 nmi = 0.926 km
- 3 nmi = 5.556 km
- 4 nmi = 7.408 km
- 7 nmi = 12.964 km
- 15 nmi = 27.78 km
- 20 nmi = 37.04 km
- 75 nmi = 138.9 km
- 200 nmi = 370.4 km
- 500 nmi = 926 km
- 2,000 nmi = 3,704 km
- 10,000 nmi = 18,520 km
Mistakes when you convert nmi to km
Dividing instead of multiplying
The nautical mile is longer, so the number of kilometres is larger. If 100 nmi gives 54, you divided.
Using 1.609
That is the statute mile factor and understates the distance by 13 per cent.
Confusing knots with miles
A knot is a speed, a nautical mile a distance. Do not mix them in one formula.
Quick answers
How many kilometres in a nautical mile?
Exactly 1.852.
How do I convert nmi to km?
Multiply the nautical miles by 1.852.
What is 100 nmi in kilometres?
185.2 km.
Is the conversion exact?
Yes, exact, because the nautical mile is defined as 1,852 m.
Does my number leave my device?
No. The calculation runs in your browser.
Related pages and a last word
If you work with lengths, these conversions are close at hand: Convert nmi to mi, Convert ly to km, Convert m to km, Convert km to mi, Convert °C to °F, Convert °F to °C, Convert L to gal, Convert gal to L, Convert cm² to m². The reverse of this page is Convert km to nmi.
In short, to convert nmi to km multiply by 1.852, remember that a nautical mile is almost twice a kilometre, and keep only the digits your measurement supports. Your number stays on your device: nothing is uploaded and no account is needed.