The formula
km/h = kn × 1.852
Where the factor comes from — each unit by its definition, then its size in SI:
1 kn = nmi / h = 0.514444444444 m/s1 km/h = km / h = 0.277777777778 m/s
Dividing the two SI sizes gives the factor: 1.852, exact — every step above is a definition, not a measurement. The reverse factor is 0.539956803456.
Kinematics and energy formulas need speed in metres per second. Road speeds come in km/h or mph, so convert before you square anything: kinetic energy goes with v², so a unit slip is squared too.
Worked examples
- Motorway driving: 53.9957 kn = 100 km/h — 53.9957 × 1.852 = 100
- A brisk walk: 2.69978 kn = 5 km/h — 2.69978 × 1.852 = 5
- US highway driving (60 mph): 52.1386 kn = 96.5606 km/h — 52.1386 × 1.852 = 96.5606
- A hard-thrown ball (30 m/s): 58.3153 kn = 108 km/h — 58.3153 × 1.852 = 108
Frequently asked questions
How many kilometres per hour is 1 kn?
1 kn = 1.852 km/h, exactly, from the unit definitions.
How do I convert kilometres per hour back to knots?
Divide by 1.852 — or multiply by 0.539956803456: 1 km/h = 0.539956803456 kn.