Convert mi to nmi miles ↔ nautical miles Free Online Secure
Type a value in miles and read it in nautical 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 mi to nmi (miles ↔ nautical miles)
| mi | nmi |
|---|---|
| 1 | 0.868976241901 |
| 2 | 1.7379524838 |
| 3 | 2.6069287257 |
| 5 | 4.3448812095 |
| 10 | 8.68976241901 |
| 20 | 17.379524838 |
| 50 | 43.448812095 |
| 100 | 86.8976241901 |
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
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.
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 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.
From the highway to the harbour: how to convert mi to nmi
Why the number gets smaller
Every American road trip ends at some water: a ferry slip in the Florida Keys, a marina on Lake Michigan, an island that can only be reached by boat. The road distance you have driven is in statute miles, while the chart that tells you how to cross the water is in nautical miles. Since a nautical mile is longer, the same distance gives a smaller number at sea. To move from one to the other you have to convert mi to nmi, and this page does it the moment you type the number.
The factor is 0.868976, the reciprocal of 1.150779. It follows from the two definitions in metres: 1,609.344 for the statute mile and 1,852 for the nautical one. Below you will find the rule, worked cases, short histories of the two miles, a comparison, the places where the conversion matters and the errors to avoid.
How to convert mi to nmi: multiply by 0.869
The rule
One statute mile is 0.868976 nautical miles. To convert mi to nmi, multiply the number of miles by 0.868976, or divide by 1.150779. 10 mi is 8.69 nmi, 50 mi is 43.45 nmi, 100 mi is 86.90 nmi and 1,000 mi is 868.98 nmi. In the reverse direction multiply by 1.1508.
Examples
A “convert mi to nmi” calculation for the drive from Miami to Key West, about 160 mi, gives 139 nmi. A ferry trip of 35 mi is 30.4 nmi. A lake crossing of 80 mi is 69.5 nmi. A coastal run of 250 mi is 217.2 nmi. The pattern is that each result is about 13 per cent smaller than the number you started with.
The mental shortcut
For a mental convert mi to nmi, subtract one eighth of the number and then a little more. For 80 mi: 80 minus 10 is 70, close to the exact 69.5. For 200 mi: 200 minus 25 is 175, near 173.8. A slightly better version is to subtract 13 per cent: 200 minus 26 is 174.
Speeds
The factor also converts miles per hour to knots. 60 mph is 52.1 knots, 30 mph is 26.1 knots and 100 mph is 86.9 knots. A motorboat advertised at 45 mph is doing 39 knots.
The statute mile
The road mile
The statute mile is 5,280 ft, 1,760 yd or 1,609.344 m. It is the mile on road signs in the United States and the United Kingdom and in the speed limits of those countries. It comes from the Roman thousand paces, adjusted by English law in 1593 so that it divides into 8 furlongs of 220 yards each.
Why Americans use it
When the United States inherited British measures, the mile came with them and has remained. The country has attempted to introduce kilometres several times without success. Road signs, odometers and maps are in miles to this day.
The nautical mile
A minute of latitude
The nautical mile is 1,852 m, 6,076 ft. It matches a minute of latitude, so sixty of them make one degree. Navigators measure distances on the latitude scale of a chart and read nautical miles directly.
International use
It is used in shipping, in aviation and in marine law. Territorial waters are 12 nmi wide. Pilots fly airways measured in nautical miles. The symbol is nmi, with NM and M used on charts.
Statute and nautical miles compared
The nautical mile is 15 per cent longer. A distance of 100 statute miles is 87 nautical miles. A speed of 30 knots is 34.5 mph. Since the knot is a nautical mile per hour, 87 knots equals 100 mph.
The two miles complement each other: one was made for land, the other for water. When you write for a mixed audience, spell out which you mean. Say "statute miles" or "nautical miles" at least once, and use mi and nmi in tables.
Where you will need it
Boating trips
A captain planning a trip from Miami to Nassau looks at a chart in nautical miles. A friend quoting 190 miles from a road atlas is not wrong, but the chart will show 165 nmi. At 20 knots the voyage takes 8.3 hours, or 190 mi at 23 mph. The skipper's view and the friend's agree once the conversion has been made.
Aviation
American pilots plan in nautical miles even though the country uses statute miles on the road. A route given as 600 mi by an airline website is 521 nmi in the flight plan, and at 140 knots a small aircraft covers it in 3.7 hours.
Weather bulletins
A storm described as 100 miles wide is 87 nmi wide. Marine forecasts describe coastal waters out to 60 nmi, which is 69 mi. If you read a forecast in miles and a chart in nautical miles, compare them after conversion.
Navigation apps
Phone navigation apps do a “convert mi to nmi” calculation for you when you change their unit setting. Choosing nautical miles on a boat gives distances to the next waypoint in the same unit as the chart. If you set statute miles, the display looks familiar, but cross-checking against the paper chart requires a mental conversion.
Lindbergh and early flights
Historic crossings
Charles Lindbergh's 1927 flight from New York to Paris covered about 3,610 statute miles, 3,137 nmi. It took 33.5 hours, an average of 108 mph, or 94 knots. Amelia Earhart's 1932 Atlantic solo flight, 2,026 mi, 1,760 nmi, took less than 15 hours.
Why it matters
Historical accounts use statute miles, while modern aviation uses nautical ones. Comparing the performance of old aircraft with modern ones requires converting both to a single unit.
Wind, waves and sea miles
Fetch
Wave height depends on fetch, the distance wind blows over open water. A fetch of 100 miles, 87 nmi, with a 30 knot wind produces waves of 3 to 4 metres. Forecasts give fetch in nautical miles; a coastal resident hearing the figure in miles should convert.
Fog and visibility
Visibility reports in the United States are in statute miles: 1 mi visibility is 0.87 nmi. Marine forecasts use nautical miles. A change in report type can make visibility look worse or better than it is.
History of two miles
The English statute mile
An Act of Parliament in 1593 defined the mile as 8 furlongs, each 40 rods of 16.5 feet. The measure was designed to be convenient for surveying farmland. It took over from the Roman mile and the old English mile of 5,000 feet.
The nautical mile
Mariners had long used the idea of a minute of latitude. By the 18th century, the length was standardised in national tables at about 6,080 feet. The 1929 conference fixed it at 1,852 m worldwide.
A worked trip from end to end
The problem
A family plans a day trip by boat: out 42 mi to an island, an hour ashore, then back. They want to know the distance in nautical miles and the fuel they need. Step one is to convert mi to nmi: 42 mi times 0.868976 is 36.5 nmi each way, 73 nmi return. At 18 knots the running time is 4.1 hours.
Fuel
The boat burns 12 gallons an hour at 18 knots, so the trip needs 49 gallons. With the one-third reserve, they should carry 66 gallons. A tank of 70 gallons is just enough. The numbers are convincing only because every figure is in the same unit system.
Reading a chart for a road-trip crew
Charts versus atlases
People who plan trips with a road atlas expect scales in miles and kilometres. A nautical chart offers a latitude scale on its sides and sometimes a small distance bar, and its colours show depth. To lay a road distance on such a chart, run the “convert mi to nmi” calculation step first, then step off the result with dividers on the latitude scale. The chart will not show roads, only coast, soundings and hazards, so a mix of the two documents is the best way to see a combined drive-and-sail trip.
A habit worth building
Write both numbers next to each leg on your trip sheet: 85 mi (74 nmi). Over a journey of many legs the sheet becomes a table in which you can see at a glance how land and sea distances compare, and where the boat saves or loses time.
Records and anniversaries
Famous distances
The first Atlantic crossing by airship, in 1919, covered about 3,200 mi, 2,780 nmi. The 1969 Moon flights covered some 239,000 mi, 207,700 nmi, to the Moon. A marathon runner covers 26.2 mi, 22.8 nmi, in a race. Numbers like these pop up in anniversary articles, where units sometimes change between paragraphs without warning.
Checking claims
If an article states that a ship travelled 600 miles in a day at 25 knots, you can check: 25 knots for 24 hours is 600 nmi, 690 mi. So either the ship was slower or the miles were nautical. A “convert mi to nmi” calculation resolves the discrepancy in seconds.
One last cross-check
Closing the loop
After any conversion, multiply your answer by 1.150779 and see whether you return to the number of miles you started with. If you do, the calculation is sound. If not, look for a misplaced decimal point or a reversed factor. This takes ten seconds and removes most of the errors that reach print.
The mile high and mile deep
Altitude in miles
Denver is at 5,280 ft, one mile above sea level, which is 0.869 nmi. Airliners cruise at 7 miles, 6.1 nmi, up. The Space Shuttle orbited at 200 mi, 174 nmi. The International Space Station is at about 250 mi, 217 nmi.
Depth
The deepest ocean, the Mariana Trench, is nearly 7 mi deep, 6.1 nmi. Oceanographers prefer metres, and altitude in aviation is in feet, so these miles are mostly used in popular accounts.
Lakes, bays and rivers
Inland waters
Lake Michigan is 307 mi long, 267 nmi. Chesapeake Bay is 200 mi long, 174 nmi. Long Island Sound is 110 mi, 95.6 nmi. Chart makers for these waters use statute miles on lake charts and nautical miles on coastal ones, so skippers learn both.
The reason
Lakes belong to the inland system of navigation, which kept statute miles from the age of river steamboats. Coastal waters belong to the maritime system, which uses nautical miles.
Planning fuel for a run
Consumption per mile
A powerboat that burns 8 gallons per hour at 25 mph uses 0.32 gallons per statute mile. At 21.7 knots it uses 0.37 gallons per nautical mile. Fuel gauges and engine manuals vary, so always check which unit your figures refer to.
Safe range
With 100 gallons and 0.37 gallons per nmi, the range is 270 nmi, or 311 mi. Keep a reserve of one third, which leaves 180 nmi, 207 mi, of usable range.
Ferry and coastal timetables
Schedules in two units
A ferry from Cape Cod to Nantucket crosses 30 mi, 26 nmi, in two hours at 13 knots. A coastal passenger vessel running 600 mi up the Inside Passage covers 521 nmi. Operators give statute miles in brochures and nautical miles in logs.
Ask for the unit
If a timetable says 45 miles, ask whether they mean land or nautical. The difference is 6 miles, enough to change the schedule by 15 minutes at slow speeds.
Spreadsheet formulas
Formula
To convert mi to nmi for a column, put miles in column A and enter =A2*0.868976 in column B. Format with two decimals. To convert mph to knots, use the same formula. For the reverse, divide by 0.868976.
Check values
Enter 1: you should get 0.868976. Enter 1.150779: you should get 1. Enter 100: 86.8976. If your result reads 115, the formula is reversed.
Rounding
Digits to keep
If the miles are given to the nearest 10, round the result to the nearest 10 as well. A distance of 120 mi is 104 nmi, so state 100 nmi if the source is rough. When you know the distance to a tenth, as in 12.4 mi, keep a tenth: 10.8 nmi.
Safety margins
When rounding for fuel or time, round the distance up. A 104 nmi trip should be planned as 105 or 110, not 100.
Teaching the idea
A classroom activity
Give each pair a map with both a statute mile scale and a nautical mile scale. They measure the same route on both scales and note the ratio. They will find 1.15 or its inverse, 0.87, whichever way they divide.
Quick exercises
Ask students to convert mi to nmi for 10, 30, 60 and 100 mi using the subtract-one-eighth method. Compare with the page. The usual error is subtracting too much or too little.
Round numbers worth remembering
A table
1 mi is 0.87 nmi; 5 mi is 4.3; 10 mi is 8.7; 25 mi is 21.7; 50 mi is 43.4; 100 mi is 86.9; 500 mi is 434.5; 1,000 mi is 869. Learning five of these lets you estimate the rest by adding.
How to interpolate
For 35 mi, take 25 mi plus 10 mi: 21.7 plus 8.7 is 30.4 nmi. The method avoids a calculator and is accurate to a tenth.
More values for convert mi to nmi
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 mi = 0.0868976 nmi
- 0.5 mi = 0.434488 nmi
- 3 mi = 2.60693 nmi
- 4 mi = 3.4759 nmi
- 7 mi = 6.08283 nmi
- 15 mi = 13.0346 nmi
- 20 mi = 17.3795 nmi
- 75 mi = 65.1732 nmi
- 200 mi = 173.795 nmi
- 500 mi = 434.488 nmi
- 2,000 mi = 1,737.95 nmi
- 10,000 mi = 8,689.76 nmi
Mistakes when you convert mi to nmi
Multiplying by 1.15
That converts in the opposite direction. From miles to nautical miles you multiply by 0.869.
Ignoring the type of mile
A source that says miles may mean either. Check the context before converting.
Mixing speed units
Do not combine mph with nautical miles in one calculation. Convert the speed to knots first.
Quick answers
How many nautical miles in a statute mile?
0.868976.
How do I convert mi to nmi?
Multiply the miles by 0.868976.
What is 100 mi in nautical miles?
About 86.9 nmi.
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 mi to ft, Convert mi to yd, Convert km to nmi, Convert nmi to km, Convert °C to °F, Convert °F to °C, Convert L to gal, Convert gal to L, Convert km² to ha. The reverse of this page is Convert nmi to mi.
In short, to convert mi to nmi multiply by 0.869, expect a result about 13 per cent smaller, and keep only the digits your measurement supports. Your number stays on your device: nothing is uploaded and no account is needed.