What's Average Cruise Speed in Miles?

I'm trying to find the average speed in mph of an average passenger jetliner. All the websites I see have the information only in knots. What is the average in mach?

Depends on the plane. From pilots I have talked to and some POM's I have for the
737, .78-.80
747, .82-.84
A knot is 1.1mph :wink:

When a jet is cruising, it measures speed in Mach number, not knots or mph. It is difficult to translate Mach into mph without a GPS, because the speed of sound varies with temperature, altitude, and atmospheric pressure, and because it doesn't take into account wind speed.

So given perfectly calm air, the ground speed in mph of an aircraft cruising at Mach 0.8 will be cruising faster if it is flying at FL350 than it would if it were flying at FL410. Temperature causes the same variation.

Additionally, Mach number doesn't take into account wind speed. So an aircraft flying at a given Mach number into a 100mph headwind will have a ground speed 100mph slower than it would if it were flying in calm air with all other things equal.

So in other words, it's going to be tough to come up with a reasonably accurate answer to your question, because airliners don't measure speed in mph.

Yes, of course the cruise speed is not written in stone. I was curious because Concorde always advertised its cruise speed at 1350 mph so I thought that all aircraft could do the same. Approximately, what would the speed be in mph from JFK to TYO using a B744? I am trying to figure-out how many hours the flight would be.

Ah, but Concorde can fly high enough in the stratosphere to eliminate some two of the variables that affect Mach-to-mph calculations: wind and pressure. Since there are fewer variations in the speed of sound, it's a lot easier to come up with a number that makes sense. And it was necessary for Concorde to advertise how much faster it was than other aircraft, given the prices they were charging to fly on it.

Again, it's hard to estimate how long a flight is going to take without knowing what the winds are going to be like...for example, I used to fly between New York and Denver rather frequently. The flight time varied from two and a half to four hours, depending on the winds. There's a bit less variation on extremely long flights because there is less variation in the wind near the North Pole, but it's still a factor.

That said, I usually use 500mph as a rule of thumb when saying "omg that's like an 18-hour flight!" I think the average speed is a bit faster than that, but you lose some time on climb and descent. And 500 is an easy number to do math on. :)