Mach (20°C, 1 atm) to Knot (UK)

Mach number is the ratio of an object's speed to the speed of sound in the surrounding medium. Mach 1 at 20°C, 1 atm equals approximately 343.6 m/s (1,235 km/h).

Mach = velocity ÷ speed_of_sound. At 20°C: Mach 1 = 343.6 m/s. Speed of sound = √(γRT/M) where γ = heat capacity ratio.

To m/s (at 20°C): × 343.6. To km/h (at 20°C): × 1,237. Note: changes with altitude and temperature.

Fighter jets (Mach 1.5–2.5), commercial aircraft (Mach 0.8–0.85), space shuttle reentry (Mach 25), and missile speeds.

Concorde: Mach 2.04. SR-71 Blackbird: Mach 3.3. X-15: Mach 6.7. Meteorites enter at Mach 50+. Subsonic <1, supersonic >1, hypersonic >5.

Thinking Mach is constant — it varies with temperature/altitude. At 30,000 ft, Mach 1 ≈ 295 m/s (colder air = slower sound).

Mach 1 = speed of sound. Below Mach 1 = subsonic. Mach 1–5 = supersonic. Above Mach 5 = hypersonic. It's a ratio, not a fixed speed.

The UK knot is a historical variation of the knot based on the British nautical mile (6,080 feet) rather than the international nautical mile (6,076.12 feet).

1 UK knot ≈ 1.853184 km/h = 0.5148 m/s. Slightly faster than the international knot (1.852 km/h).

To international knots: × 1.00064. To km/h: × 1.853. To m/s: × 0.5148.

None in modern use. Only relevant for interpreting historical British naval records.

The difference between UK and international knots is only 0.064% — barely noticeable but important for precise navigation.

Assuming all old British ship logs use the same knot as today — they don't, but the difference is tiny.

Historical only. Effectively identical to modern knot. Only matters for historical maritime research.