What Does “Mach” Mean?

The measurement of speed is a common question; sometimes aircraft speed is measured in knots and sometimes it’s measured in Mach.

But what are these measurements and how do they relate to ground or nautical speed measurements, such as miles or kilometers per hour? Let’s break it down:

What is a knot?

A knot (often abbreviated as “kts”) is a unit of measurement of speed, with one knot equal to one nautical mile per hour.

Knots is the speed that the pilot uses as he flies – the air speed indicator inside a flight deck measures knots – just as a car driver would give the driver a speed in miles per hour. Knots were traditionally used in maritime navigation before airplanes were invented.

The nautical mile is based on the circumference of the earth. If you take a slide of the earth through the equator, you get a flat circle which can be divided into 360 degrees (as if you were navigating using a compass). Each degree can be split into 60 equal parts called minutes, and the length of one of these minutes equals one nautical mile.

By comparison, 1 nautical mile is equal to 1.15 miles.

What is Mach?

The Mach number describes the aircraft’s speed compared with the speed of sound in air, with Mach 1 equating to the speed of sound. It is named after Ernst Mach, an Austrian physicist, who first devised the measurement.

Concorde famously made the trip from London to New York in an average time of three hours and 30 minutes, cruising just above Mach 2 – aka flying at twice the speed of sound. Mach numbers are very useful when it comes to measuring the speed of aircraft traveling close to or beyond the sound barrier.

So if you’re looking for the fastest and most innovative aircraft, it’s often useful to use Mach numbers.

What is the fastest private jet aircraft and how fast does it fly?

The two current contenders for the speed crown are the Gulfstream G650 and Cessna Citation X+, which can both fly at speeds just above Mach 0.92 (just under the speed of sound).

The Citation X has recorded a top speed of Mach 0.935, narrowly beating the G650. However in an average flight, the two achieve similar average speeds.

But of course, there are some supersonic private jets that are in development, anticipating to have a Mach number of 1 and above. The Aerion Corporation’s trijet AS2, which will reportedly travel at Mach 1.6, is currently the main contender.

What is a sonic boom?

With environmental considerations a big focus for the future of aviation development, regulation around noise impact is a major issue holding back the new era of supersonic flight. When an aircraft goes above Mach 1 – the speed of sound – it will create a pressure wave, known as a sonic boom. And the larger the aircraft, the larger the boom.

In order to negate this, new technologies are beginning to emerge that muffle these booms, making them a key development in making supersonic private jets a reality within the next six to ten years.

How fast do other popular private jets fly?

Here are a few examples of existing, popular private jet aircraft and their cruising speeds in knots, alongside their Mach numbers:

Aircraft type

Cruising speed (Knots)

Mach number

Cessna Citation X



Gulfstream G650



Embraer Legacy 650



Cessna Citation XLS+



Embraer Phenom 300



Embraer Phenom 100



Cessna Citation Mustang



*The cruising Mach number depends on the length of the flight. An ultra-long range flight would fly slightly slower to save fuel.

If you want to compare private jet aircraft speeds for a specific itinerary, our team can help. Contact us online or call us at (866) 726-1222