Mach (SI Standard) to Knot (UK)

Mach (SI standard) uses the speed of sound at 0°C and 1 atm (295.0464 m/s) as the reference, based on SI standard conditions.

Mach (SI) = velocity / 295.0464 m/s. At 0°C, 1 atm: speed of sound ≈ 295 m/s (colder than 20°C).

To m/s (at 0°C): × 295.05. To km/h (at 0°C): × 1,062. To Mach (20°C): × 0.859.

Rarely used in practice. Theoretical aerodynamics at SI conditions, some scientific papers.

Mach 1 (SI) = 295 m/s, while Mach 1 (20°C) = 343.6 m/s. Same Mach number, different actual speeds depending on definition.

Assuming all Mach numbers use the same reference — they don't. Always check temperature and pressure conditions.

Rarely encountered. Mach 1 (SI) = 295 m/s at 0°C. Standard aviation Mach uses different conditions. Know your reference!

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.