AeroCalc

Mach Number Calculator

Velocity divided by the speed of sound — the number that defines flight regimes.

Object speed (m/s)

Speed of sound (m/s)

Mach number

1.983

Ma = v / c

What you entered

Object speed (m/s): 680Speed of sound (m/s): 343

1
Mach number: Ma = v / c
680 / 343= 1.9825
2
Flight regime
Ma = 1.9825= Supersonic

Result

Mach number: 1.983

At 680 m/s (2,448 km/h), Mach 1.983 — supersonic flight.

Mach number and flight regime

Mach number is the object's speed divided by the local speed of sound, taken here as 343 m/s at sea level.

Speed (m/s)	Speed (km/h)	Mach number	Regime
100	360	0.2915	Subsonic
200	720	0.5831	Subsonic
343	1235	1.0000	Transonic
500	1800	1.4577	Supersonic
686	2470	2.0000	Supersonic
1200	4320	3.4985	Supersonic

The speed of sound is not constant - it falls with temperature, so at cruising altitude it is nearer 295 m/s and an aircraft reaches a given Mach number at a lower true airspeed. That is why aircraft are limited by Mach rather than by speed: the drag rise and shock formation depend on the ratio, not the absolute velocity. The transonic band around Mach 1 is the difficult region, where parts of the airflow are supersonic while others are not, which is what made early attempts at the sound barrier so dangerous.

The four flight regimes

Subsonic (Mach < 0.8) is normal commercial aviation; transonic (0.8–1.2) is where shockwaves first form and aerodynamics get tricky; supersonic (1.2–5.0) is Concorde and fighter jets; hypersonic (> 5.0) is re-entry vehicles and experimental scramjets. Each regime requires fundamentally different engineering.

Why the speed of sound changes with altitude

The speed of sound depends on temperature — at sea level (15°C) it's about 343 m/s, but at 35,000 ft (-56°C) it drops to about 295 m/s. This means the same aircraft velocity corresponds to a higher Mach number at altitude, which is why jets measure airspeed in Mach rather than km/h.

Frequently asked questions

A bullet travels at 900 m/s at sea level. What's its Mach number?

Mach = v/v_sound = 900/343 = 2.62 — supersonic (Mach 1.2-5.0). The bullet creates a shock cone with half-angle sin(θ) = 1/M = 1/2.62 → θ = 22.4°. This is the 'crack' you hear after a supersonic bullet passes.

Why does the Concorde fly at Mach 2 but commercial jets stay below Mach 0.85?

Above Mach 0.8, shockwaves form on the wing, dramatically increasing drag and fuel consumption. The Concorde's supersonic engines and delta wing accepted this penalty for speed; commercial jets optimize for fuel efficiency at Mach 0.78-0.85 (transonic regime). Concorde used 4× more fuel per passenger-mile.

What is the speed of sound on Mars?

Mars's thin CO₂ atmosphere at -60°C gives a speed of sound of only ~240 m/s (vs. 343 m/s on Earth). The Ingenuity helicopter's blade tips approach Mach 0.7 on Mars — they'd be subsonic on Earth but near transonic on Mars, which complicates blade design.

What happens exactly at Mach 1?

At Mach 1, pressure waves can't escape ahead of the object — they pile up into a shock wave (sonic boom). Drag peaks at the 'sound barrier' (about Mach 0.95-1.05), and aircraft need significantly more thrust to push through it. Once past, drag actually decreases slightly.