How long is the drive from Austin to Phoenix?

Question

and at what speed?

Answer 1

It would probably be 2 days minimum to drive. It might be 12 to 20 hours depending on how fast you drive and if you take rest.

Answer 2

I would say that if you only use the Interstates and start out very early in the morning, you could reach Phoenix by the evening. That includes rest and gas stops as well as a speed of around 70 MPH for much of the way. Otherwise, you could get there in about a day and a half. It depends on how quick you want to get there.