The conversion
Kilometres in. Nautical miles out.
Every kilometre is 0.54 of a nautical mile. That is not an analogy. It is the same distance, in the unit we actually use.
The converter needs JavaScript to do the arithmetic. Every other word on this site reads without it. A kilometre is 0.54 of a nautical mile, if you would rather do it by hand.
No entry
Put a distance in. The figures fill themselves.
The arithmetic
There is no conversion factor to argue about.
A nautical mile is defined as 1,852 metres exactly. Not approximately, not by convention: that is the definition, agreed in 1929 and unchanged since. It comes from the length of one minute of latitude, which is why it is the unit that makes sense on a chart.
So a kilometre is 1000 / 1852 of a nautical mile, which is 0.5399568 and a bit. The converter carries the full precision and rounds only at the last step, when it prints the figure. Rounding first and multiplying afterwards is how you end up two tenths of a mile out over a marathon.
Miles work the same way. A statute mile is 1,609.344 metres exactly, so it is 0.868976 of a nautical mile. Switch the unit on the converter and it uses the right factor; it does not convert to kilometres first and then convert again.
1 km = 0.5399568 NM · 1 NM = 1 852 m · 110 kt
Reference
The distances you already know, in miles you can picture.
Block time is what the distance would take in a Cessna 172 at 110 knots true, which is the number this site uses everywhere. It is cruise in still air, so treat it as a yardstick rather than a flight plan.
| Distance | Kilometres | Nautical miles | Block time in a 172 | At the anchor rate |
|---|---|---|---|---|
| Parkrun | 5.00 | 2.70 | 1.5 min | Kč 67.49€2.70$2.70 |
| 10K | 10.00 | 5.40 | 2.9 min | Kč 134.99€5.40$5.40 |
| Ten miles | 16.09 | 8.69 | 4.7 min | Kč 217.24€8.69$8.69 |
| Half marathon | 21.10 | 11.39 | 6.2 min | Kč 284.79€11.39$11.39 |
| Marathon | 42.20 | 22.78 | 12.4 min | Kč 569.59€22.78$22.78 |
| 50 km ultra | 50.00 | 27.00 | 14.7 min | Kč 674.95€27.00$27.00 |
| 100 km ultra | 100.00 | 54.00 | 29.5 min | Kč 1,349.89€54.00$54.00 |
What it buys
A marathon is about twenty-three minutes of flying.
That is the honest scale of it. A marathon converts to 22.79 nautical miles, which at 110 knots is a little over twenty minutes in the air. Nobody is funding a type rating with one race.
Which is the point, not a problem. The club is a few hundred people each turning an ordinary week of running into an ordinary amount of money, repeatedly. A single donation is a rounding error and a year of them is a scholarship.
The rate is an anchor rather than a price. Move it up if the month allows and down if it does not. The arithmetic is the same either way, and nobody sees what you set it to.
Why nautical miles
Because it is the unit we already use.
A nautical mile is 1,852 metres exactly, by definition. It is the unit aviation uses for distance, alongside knots for speed and feet for altitude. A 10K is 5.40 NM, and unlike 10 kilometres, that is a distance you can picture from the left window.