Convert nmi to mi nautical miles ↔ miles Free Online Secure
Type a value in nautical miles and read it in miles 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 mi (nautical miles ↔ miles)
| nmi | mi |
|---|---|
| 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
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.
Is a mile the same everywhere?
The statute mile on this page is 1609.344 m exactly, which follows from the 1959 inch. The nautical mile is a different unit altogether, 1852 m exactly, defined as one minute of arc along a meridian. The two are not variants of one another and should never be swapped.
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.
Two miles that are not the same: how to convert nmi to mi
English has more than one mile. The mile on a road sign in Britain or America is the statute mile, 5,280 feet. The mile in a weather bulletin, a ship's log or a flight plan is the nautical mile, 6,076 feet. They share a name and a symbol in careless writing, but they differ by 15 per cent, which over a long crossing means a good many miles. Whenever a sea or air distance has to be set against a road distance, you need to convert nmi to mi, and this page does it as you type.
The ratio is 1.150779, a figure that comes from dividing 1,852 metres by 1,609.344 metres. It is not tidy, but it is exact in the sense that both miles are defined in metres. The sections below show the rule, give worked cases, tell you where each mile came from, compare them, explain where the conversion matters and list the errors that occur most often.
How to convert nmi to mi: multiply by 1.1508
The rule
One nautical mile equals 1.150779 statute miles. To convert nmi to mi, multiply the number of nautical miles by 1.150779. 10 nmi is 11.51 mi, 50 nmi is 57.54 mi, 100 nmi is 115.08 mi and 1,000 nmi is 1,150.78 mi. To go the other way, divide by 1.150779 or multiply by 0.869.
Worked cases
After a “convert nmi to mi” calculation, a ship 25 nmi from a port is 28.8 mi away. A flight of 450 nmi is 517.8 mi. A storm 80 nmi off the coast is 92.1 mi out. A harbour 3 nmi across is 3.45 mi wide. The rule of thumb is to add about 15 per cent.
The mental method
For a mental convert nmi to mi, take the nautical miles, add one tenth, then add one more twentieth of the original. For 100: 100 plus 10 plus 5 is 115, against the exact 115.08. For 60: 60 plus 6 plus 3 is 69, against 69.05. The method is accurate to a tenth of a per cent.
Speeds
The same factor converts knots to miles per hour. 20 knots is 23 mph; 100 knots is 115 mph. A hurricane wind of 64 knots is 73.7 mph, and weather reports use either unit depending on the country.
The nautical mile
Sea and air
The nautical mile is 1,852 m or 6,076.1 ft. It is tied to the Earth: one minute of arc of latitude. Sailors and pilots like it because a position in degrees and minutes of latitude gives distances directly. The symbol is nmi; navigators write NM or M.
Standardisation
An international conference in 1929 fixed the nautical mile at 1,852 m, and the United States adopted the value in 1954, Britain in 1970. Until then, the British Admiralty mile of 6,080 ft and the American mile of 6,080.2 ft were used.
The statute mile
Eight furlongs
The statute mile is 5,280 feet, 1,760 yards or 1,609.344 m. It descends from the Roman mille passus, a thousand paces, and was fixed in England by statute in 1593, hence the name. It is the mile used on road signs in the United States and the United Kingdom.
The foot and the yard
Because the statute mile is defined from the foot and the yard, which were defined from the metre in 1959, it equals exactly 1,609.344 metres. The nautical mile, by contrast, is related to the metre by its own definition. The ratio of the two is therefore a fixed decimal.
Nautical and statute miles compared
A nautical mile is 15.08 per cent longer than a statute mile. Over 100 miles the difference is 15 miles, which matters to a boat running low on fuel or a plane with a headwind. Speeds scale in the same way: 100 knots is 115 mph, so a ship at 20 knots is travelling faster than the number suggests to a land-based reader.
When you write, use nmi for the nautical mile and mi for the statute mile, and avoid the bare word mile for water or air distances. If the source says miles in a nautical context, treat it as nautical until proven otherwise.
Where you will need it
Hurricane and storm reports
The National Hurricane Center reports wind speed in knots and miles per hour, and distances in nautical miles and statute miles. A hurricane with a radius of tropical-storm-force winds of 150 nmi covers 172.6 mi. A storm that is 200 nmi from the coast is 230 mi away, not 200.
Boating in the United States
American charts use nautical miles, but many marinas quote the distance to the next harbour in statute miles because their customers think in road distances. A trip of 40 nmi is 46 mi on a land map. At a cruising speed of 8 knots, the passage takes 5 hours.
Aviation
An American pilot files flight plans in nautical miles and quotes ground speed in knots, yet airline passengers see statute miles on loyalty cards. A flight of 1,400 nmi is 1,611 mi. The two numbers are in the same ballpark, which makes it easy to forget which one is which.
Sports and records
Open-water swimming events are measured in kilometres. A famous channel swim of 21 mi across the Strait of Dover covers 18.2 nmi. Records for sailing round the world use nautical miles, and a day's run of 700 nmi is 806 mi.
The Great Lakes and inland seas
Charts for inland water
On the Great Lakes, charts show statute miles and nautical miles. Lake Superior is 350 mi long at its greatest, 304 nmi. Ships measure their trips in statute miles, because the lake shipping industry kept the land unit, while ocean-going vessels measure in nautical miles. A captain who moves from the lakes to the sea has to learn the other mile.
Rivers
Rivers such as the Mississippi are marked in statute river miles. The distance from St. Louis to New Orleans is about 1,060 river miles, 921 nmi. Towboats compute fuel and time with the miles of their route.
Radar, radio and horizon
Distance in either mile
A marine radar with a range of 24 nmi sees 27.6 statute miles. A VHF radio reaching 25 nmi reaches 28.8 mi. The horizon from a bridge 20 m above the water is 9 nmi, 10.4 mi.
The formula
In nautical miles, the horizon is 1.17 times the square root of the eye height in feet. In statute miles it is about 1.35 times that root. The ratio is the same factor.
Rescue and coast guard work
Search areas
A search area may be defined as a box of 20 by 30 nmi, 23 by 34.5 mi. The coast guard reports in nautical miles, while news outlets usually convert to statute miles. If you see two different figures for the same search area, it is usually the same dimension in two units.
Time to reach
A helicopter at 120 knots reaches a target 90 nmi away in 45 minutes. The same journey is 103.6 mi at 138 mph.
A worked example: crossing a bay
Distance and time
A ferry crosses a bay of 18 nmi at 22 knots. The crossing takes 0.82 hours, 49 minutes. In statute miles the distance is 20.7 mi and the speed 25.3 mph. Passengers who think in miles hear the same story whichever unit is used. A skipper who needs a “convert nmi to mi” calculation for the fare table can do it in seconds.
What to remember
The time does not change when the unit does. If one figure is converted, the other must be converted with it, or the result will be wrong. This is the single most important point of any unit conversion.
Reading two news stories at once
When the figures disagree
Suppose one article says a ship went down 120 miles off the coast and another says 104 miles. The two may describe the same position: 120 statute miles is 104.3 nmi. A reader who suspects an error should run the “convert nmi to mi” calculation before deciding that one of the reports is wrong. Journalists sometimes convert without telling readers, so the unit in print may not be the one the source used.
Good habits for writers
State the unit each time, give the other in brackets and keep the same pair throughout. For example: 120 nmi (138 mi) offshore. A reader can then follow the story whichever mile they know.
Planning a coastal cruise in miles
Legs and stops
An American couple plans to cruise 360 statute miles along a coast in six legs of 60 mi each. Marina guides, however, list distances in nautical miles, so each leg of 60 mi is 52.1 nmi. To compare their plan with the guide they convert nmi to mi for every leg, then add the legs to find the total, 312.8 nmi. At a cruising speed of 7 knots, a leg takes 7.4 hours, a full day with breaks.
Weather windows
Forecasts are issued in knots and nautical miles, so wind speeds and distances to fronts come in the sea's unit. A front 150 nmi away moving at 20 knots arrives in 7.5 hours; the couple should plan to reach port well before then.
Knots and miles per hour
Speed tables
5 knots is 5.75 mph, 10 knots 11.5 mph, 15 knots 17.3 mph, 20 knots 23 mph, 30 knots 34.5 mph, 40 knots 46 mph. A fast ferry at 35 knots makes 40.3 mph, a motorway speed. A sailboat at 6 knots moves at 6.9 mph, about a jogging pace.
Wind scales
The Beaufort scale is given in knots and in mph. Force 8, a gale, is 34 to 40 knots, 39 to 46 mph. Force 10, a storm, is 48 to 55 knots, 55 to 63 mph. Hurricane force starts at 64 knots, 74 mph.
Mapping and the 60 to 1 rule
Latitude and miles
One degree of latitude is 60 nmi, which is 69.05 statute miles. A navigator moving from 30 to 35 degrees north covers 300 nmi or 345.2 mi. The 69 miles per degree rule is useful for people who use road atlases.
Longitude varies
A degree of longitude equals 60 nmi at the equator, but shrinks toward the poles. At 45 degrees latitude it is 42.4 nmi, 48.8 mi. The nautical mile is tied to latitude, not longitude.
Why the miles differ
Different problems, different units
The statute mile developed for land travel and land measurement, in a world where distances were counted in steps. The nautical mile came from navigation, where the main task is to locate a position on a sphere. A unit matched to the minute of arc saves a conversion at every step. That is why the two have lived side by side for centuries.
The modern accommodation
GPS devices let you set the distance unit as you like: nautical, statute or kilometre. Aviation and marine standards keep nautical, and road navigation keeps kilometres or statute miles. A good display shows the unit next to the number.
Spreadsheets and calculators
Formula
To convert nmi to mi for a column, put nautical miles in column A and enter =A2*1.150779 in column B. Format with two decimals. To convert knots to mph, use the same formula. To reverse, divide by 1.150779.
Testing
Enter 1 and check the result is 1.150779. Enter 100 and confirm 115.0779. If you get 100 times 1.15, you are using a rounded factor, which is fine for estimates.
Rounding and significant figures
Match the input
A distance of 25 nmi, given to two significant figures, is 29 mi, not 28.77. If the nautical miles are measured to a tenth, as in 25.3 nmi, the answer is 29.1 mi.
Do not round the factor early
Use the full 1.150779 for the calculation and round the answer. Using 1.15 loses 0.07 per cent, which on a 3,000 nmi voyage is 2 mi. Not much, but unnecessary.
Fuel and range
Miles per gallon
Boats compute fuel use in gallons per nautical mile or nautical miles per gallon. A boat doing 2 nmi per gallon covers 2.3 statute miles per gallon. A car doing 30 mpg is therefore far more efficient than the boat, though its mile is shorter.
Range calculation
A tank of 200 gallons at 2 nmi per gallon allows a 400 nmi range, 460 mi. With a safety reserve of 20 per cent, the usable range is 320 nmi, 368 mi.
Teaching two miles
A map exercise
On a chart of the Gulf of Mexico, measure a route with the latitude scale in nautical miles, then with the printed statute mile scale. Compare the results. Students see that the same line gives two numbers differing by 15 per cent, and learn why units matter.
Mental practice
Ask students to convert nmi to mi for 10, 20, 50 and 100 nautical miles using the add-a-tenth-and-a-twentieth method. Check with the page. Mastering a single technique avoids reaching for a calculator.
Cruise and ferry timetables
Reading the brochure
Cruise brochures list itineraries with distances in nautical miles; ferries list them in statute miles or kilometres, depending on the country. A cruise of 3,200 nmi over 14 days is 3,682 mi. That means an average of 263 mi a day, a relaxed pace.
Choosing a route
If one itinerary shows 1,200 nmi and another 1,300 mi, the second is shorter, because 1,300 mi is 1,130 nmi. A comparison needs a common unit.
More values for convert nmi to mi
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 = 0.115078 mi
- 0.5 nmi = 0.57539 mi
- 3 nmi = 3.45234 mi
- 4 nmi = 4.60312 mi
- 7 nmi = 8.05546 mi
- 15 nmi = 17.2617 mi
- 20 nmi = 23.0156 mi
- 75 nmi = 86.3085 mi
- 200 nmi = 230.156 mi
- 500 nmi = 575.39 mi
- 2,000 nmi = 2,301.56 mi
- 10,000 nmi = 11,507.8 mi
Mistakes when you convert nmi to mi
Dividing instead of multiplying
The nautical mile is longer, so the number of statute miles is larger. If 100 nmi gives 87, you divided.
Treating the miles as equal
A bare mile may be either. Check the source.
Applying the factor to speed only
If you convert a speed from knots to mph, convert distances as well. Mixing leads to wrong times.
Quick answers
How many statute miles in a nautical mile?
1.150779.
How do I convert nmi to mi?
Multiply the nautical miles by 1.150779.
What is 100 nmi in miles?
About 115.08 mi.
Is the conversion exact?
Yes, to the digits shown, because both miles are defined in metres.
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 km, Convert yd to mi, Convert km to mi, Convert mi to yd, Convert °C to °F, Convert °F to °C, Convert L to gal, Convert gal to L, Convert ft/s to mph. The reverse of this page is Convert mi to nmi.
In short, to convert nmi to mi multiply by 1.1508, add roughly 15 per cent, and keep only the digits your measurement supports. Your number stays on your device: nothing is uploaded and no account is needed.