How fast is the Flash? Barry himself is wondering that...
Of course, if the CW is right, than mankind has already invented several vehicles that should have pilots (and the X-Men!!) traveling through time on a regular basis (click to embiggen):
But the comic book? Well, sadly, "Roemers" never caught on as a multiplier for the speed of light, because, well, science sort of mostly says that physical objects cannot exceed the speed of light. So multiple of that would be useless (and please don't go on about tachyons and other hypothetical particles, because they haven't been actually discovered, and most scientists think they couldn't exist). In cases where the effective travel speed, via "hyperspace" or "warp drive" or what have you, appears to be faster than light, we've been stuck with "warp factors" or just mundane measurements like "light years" or "parsecs" or what have you. Sorry, Ole Christensen Rømer (his actual name), your name just didn't stick!
However, this is DC Science, Silver Age style, so the Flash has already traveled seven times the speed of light. Can he do 10?!?!
Plus, Barry has invented a device that will measure velocity to 10 times the speed of light?!? Why the hell isn't he winning the Nobel Prize for physics, instead of working in the podunk crime lab in Central City?
Of course, it did (temporarily) give him the power to read minds (what???) and give some thieves he bumped into the power of telekinesis (WHAT?!?!?!)!! DC Science, man...DC Science.
So, the TV show leaves Barry way to slow (but conveniently able to travel through time) whereas the comics make him impossibly fast. The choice is yours....As for me? No way can I live with a Flash who can only achieve Mach-2. Free Barry Allen!!
Comic books portions are from Flash #150 (1965)