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[The Flash - TV] How does Flash know how fast he is going or how far he has gone? Spoilers from this week's episode

How does Flash know how fast he is going or how far he has run?  In many episodes he asks how fast he has to go, but it is unclear how he knows his speed, especially when they aren't reporting his speech to him.  This week he ran 5.3 miles without GPS / backup, then runs exactly 838 mile per hour seemingly without any external confirmation of his current speed.
gpt
He's been shown to have an extremely analytical mind, to the point he's able to accurately measure wheel width without the use of any kind of measuring device.

He's been running on the STAR Labs treadmill, so he's gotten a feel for how fast he's able to cover ground at certain speeds, and on top of that he was running inside a city, which has standards for the sizes of city blocks. That takes care of the distance.

Speed is also likewise pretty easy - accelerate as hard as he can until he finally breaks the sound barrier, then accelerate a bit more until it "feels" like the right speed.

There's also the fact that, while not explicitly named, he's likely got access to the Speed Force which grants some degree of intuition on the speed the runner is going. Every time he gets up to a certain speed or readies a new stunt (see the train rescue from a few weeks earlier), his eyes crackle with electricity - and of course he's often trailed by similar lightning while running.