Convert Mach to Knot (Ma → kn)

Converting Mach to knots is straightforward: multiply by the conversion factor. Follow these three steps to do it by hand or in your head.

1. 1
   Take your value in Mach

   Start with the number of Mach (Ma) you want to convert.
2. 2
   Multiply by 661.47085

   The conversion factor from Ma to kn is 661.47085. Multiply your value by this number.
3. 3
   Read the result in knots

   The result is your value in knots (kn).

Multiply the value in Mach by 661.47085. For the reverse direction, multiply by 0.001512.

• ✓Mach 1 = ~1225 km/h at sea level, standard conditions.
• ✓Local speed of sound decreases with altitude (colder air) — true Mach value varies.
• ✓Mach 0.8+ is "transonic"; Mach 1+ supersonic; Mach 5+ hypersonic.

• ✗Assuming Mach 1 is a fixed speed — depends on altitude and temperature.
• ✗Multiplying Mach values as simple ratios across altitudes.
• ✗Using Mach for subsonic everyday speeds — not practical.

What is the Mach?

Mach is a dimensionless speed ratio comparing an object's speed to the local speed of sound (about 343 m/s in air at sea level, varying with altitude and temperature). Named after Austrian physicist Ernst Mach (1838–1916), who pioneered supersonic photography, the unit became standard with high-speed aviation. Mach 1 = sound speed; Mach 2 = twice sound speed. The Concorde cruised at Mach 2.04, the SR-71 Blackbird reached Mach 3.3, and modern commercial jets cruise at Mach 0.78–0.85 (subsonic). 'Breaking the sound barrier' (first achieved by Chuck Yeager in 1947) means crossing Mach 1 in horizontal flight. Hypersonic missiles operate above Mach 5. Mach is essential in aerodynamics because shock waves, drag, and heating all depend on the relationship between vehicle speed and sound speed. At sea level: Mach 1 ≈ 1,235 km/h ≈ 767 mph ≈ 343 m/s.

• Military and supersonic-aircraft speeds
• Aerospace engineering
• Hypersonic missile specifications

What is the Knot?

The knot equals exactly one nautical mile per hour (1.852 km/h or 0.5144 m/s) and is the universal speed unit for ships and aircraft worldwide. The name derives from the historical practice of measuring ship speed by counting knots tied at regular intervals along a 'log line' that was let out over the stern of a ship — the number of knots that passed in a given time gave the speed. International maritime regulations, aviation flight plans, and weather reports for sailors all use knots. A typical cruise ship sails at 18–22 knots, container ships at 18–25 knots, and commercial airliners at 470–500 knots cruise speed. The knot relates to km/h (1 knot ≈ 1.852 km/h), mph (1 knot ≈ 1.151 mph), m/s (1 knot ≈ 0.514 m/s), and the nautical mile (1 knot = 1 nmi/h). Wind speeds in aviation are also given in knots.

• Ship speeds and ocean currents
• Aircraft airspeed and ground speed
• Marine weather (wind reports in knots)