Nautical miles vs kilometres in aviation: get the exact conversion, why pilots use NM, how knots relate, and how to avoid unit mistakes.
In aviation and real-world flying, a nautical mile (NM) is exactly 1,852 metres, while a kilometre (km) is exactly 1,000 metres. One nautical mile therefore equals 1.852 km, and one kilometre equals about 0.540 NM. Aviation favours nautical miles because they fit geographic coordinates and speeds measured in knots.
Why does aviation use nautical miles instead of kilometres?
Aviation uses nautical miles because they have a practical connection to navigation across the Earth. A nautical mile originated as approximately one minute of latitude, while geographic positions are expressed in degrees and minutes.
The modern nautical mile is a fixed unit of exactly 1,852 metres. An actual minute of latitude varies slightly with position because the Earth is not a perfect sphere, so it should not be treated as the unit's precise modern definition.
Nautical miles also pair directly with knots: one knot means one nautical mile per hour. That keeps flight-planning calculations straightforward and explains why aircraft speed is normally expressed in knots.
How do you convert nautical miles to kilometres?
Multiply nautical miles by 1.852 to obtain kilometres; divide kilometres by 1.852 to obtain nautical miles.
NM × 1.852 = kmkm ÷ 1.852 = NMkm × 0.539957 = NM
| Distance | Converted distance |
|---|---|
| 1 NM | 1.852 km |
| 5 NM | 9.26 km |
| 10 NM | 18.52 km |
| 25 NM | 46.3 km |
| 50 NM | 92.6 km |
| 100 km | 53.996 NM |
For a quick estimate, multiply NM by 1.85. The mistake we see most often is using 1.609, which converts statute miles—not nautical miles—to kilometres. One nautical mile is about 1.151 statute miles.
Aviation normally uses the symbol NM; some software uses nmi. In formal SI notation, lowercase nm means nanometre, although simulator interfaces do not always observe that distinction.
How do knots relate to nautical miles and kilometres?
One knot is exactly one nautical mile per hour, which is exactly 1.852 kilometres per hour. A flight covering 90 NM at a groundspeed of 120 knots therefore takes 0.75 hours, or 45 minutes.
Use groundspeed, not indicated airspeed, when calculating arrival time. Wind can make 120 KIAS correspond to a very different groundspeed. Our guide to converting knots and metric speed units covers the related speed arithmetic.
Keep the units paired: divide NM by knots, or kilometres by km/h. Dividing nautical miles by km/h is a common source of incorrect fuel and time estimates.
When can nautical-mile readings be misleading?
A nautical-mile display can be accurate while measuring something different from the flat map distance a pilot expected. The unit, reference point and measuring method all matter.
DME shows slant range. It measures the direct distance between the aircraft and the ground station, not purely horizontal distance. An aircraft almost overhead but 6,000 feet above the antenna will still indicate roughly 1 NM. GPS and flight-management systems typically calculate waypoint or route distance differently; our explanation of GPS, DME and aircraft navigation readouts sets out those distinctions.
Route distance is not direct distance. A flight plan following airways, procedure legs or diversions will be longer than a straight line between airports. The remaining distance may also change when the active leg sequences or a shortcut is entered.
Simulator settings may not control cockpit avionics. A simulator's map or electronic flight bag may show kilometres while the aircraft's navigation display remains in NM. We recommend checking the label beside each value rather than assuming the regional unit setting applies everywhere.
Nautical miles are not used for every aviation measurement. Runway lengths are commonly published in metres or feet, altitude is usually expressed in feet but may be given in metres in some operations, and visibility can be reported in metres, kilometres or statute miles. In an ATC navigation or separation instruction, however, an unqualified distance in “miles” normally means nautical miles unless local procedures say otherwise.