Speed Converter

Speed is expressed differently across road, aviation, and maritime contexts. 1 mph = 0.44704 m/s (exact, NIST SP 811) and 1 knot = 1852/3600 m/s (exact; 1 nautical mile = 1852 m, BIPM). Type any speed and all others update live; click any result to use it as the new input.

The formula

All conversions route through meters per second (m/s) as base:

target = value × (fromUnit_to_ms / toUnit_to_ms)

For mph to km/h:

km/h = mph × (0.44704 / (5/18)) = mph × 1.609344

For knots to mph:

mph = knots × (1852/3600) / 0.44704 = knots × 1.15078

Practical examples

Example 1 — Speed limit comparison (mph to km/h)

A US highway speed limit is 65 mph. What is the equivalent for a Canadian driver used to km/h?

65 × 1.609344 = 104.61 km/h

Example 2 — Aircraft cruise speed (knots to km/h)

A commercial aircraft cruises at 450 knots. What is that in km/h?

450 × 1.852 = 833.4 km/h

Example 3 — Wind speed (m/s to mph)

A weather report shows wind at 12 m/s. What is that in mph?

12 / 0.44704 = 26.84 mph

Common mistakes

Mistake 1 — Confusing knots and mph as roughly equal

One knot is 1.151 mph — not 1 mph. At airspeeds of 450 knots, treating knots as mph understates speed by about 68 mph. The distinction matters in aviation and maritime navigation.

Mistake 2 — Using 1.6 instead of 1.60934 for mph to km/h

The exact factor is 1.609344. At 100 mph, rounding to 1.6 gives 160 km/h instead of 160.93 km/h — a 0.6% error. For everyday use this is acceptable; for engineering or official records, use the exact factor.

International and regional variations

Quick reference: common speed conversions