Convert kilometers per hour to miles per hour. The ratio is the same exact 1.609344 that relates the two distance units, because an hour is an hour on both sides.
mph = km/h ÷ 1.609344
NIST SP 811 (2008), Appendix B.8 — mile per hour (mi / h) to kilometer per hour (km / h) = 1.609 344 E+00
Speed conversion inherits its factor from distance: the hour cancels out, so kilometers per hour to miles per hour uses exactly the same 1.609344 that converts the distances themselves. This is the conversion drivers need when a rental car shows the wrong unit, and the one sailors avoid entirely by using knots, which are nautical miles per hour rather than statute ones.
mph = km/h ÷ 1.609344
Because both scales measure distance over the same unit of time, the time cancels and only the distance factor remains. NIST publishes the same number for the speeds as for the lengths.
| kilometers per hour | miles per hour |
|---|---|
| 10 | 6.2137119 |
| 30 | 18.641136 |
| 50 | 31.06856 |
| 60 | 37.282272 |
| 80 | 49.709695 |
| 90 | 55.923407 |
| 100 | 62.137119 |
| 110 | 68.350831 |
| 120 | 74.564543 |
| 130 | 80.778255 |
| 140 | 86.991967 |
A number that disagrees with its source is a defect, not a rounding preference.
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Convert kilometers to miles instantly in your browser. One mile is exactly 1.609344 kilometers, the factor fixed by the international yard and pound agreement.
Convert miles to kilometers in your browser. One mile is exactly 1.609344 kilometers, so the answer is a fixed ratio rather than an approximation.
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