It isn't. Star Trek has sometimes contradicted itself, and "warp factor" is just a pseudoscientific term that has varied over the years
Kirk's original Enterprise had done something like Warp 14, but that The Enterprise D from TNG could only do Warp 9.6 Voyager could do 9.975 and so on. Aparently Gene Roddenbury rearranged the scale from the original 60's series for Next Gen, and so where the eponymous series' Enterprise fits, I have no idea.
But...
I found this online...
According to page 54 of the Star Trek Technical Manual:
Warp 1 = Speed of light
Warp 2 = 10 times the speed of light
Warp 4 = 100 times the speed of light
Warp 8 = 1000 times the speed of light
If you like maths, try here
Or just realise that The Enterprise will either a) arrive just in the nick of time or b) arrive just a moment to late to avert a tragedy, regardless of how warped it's factors are
Kirk's original Enterprise had done something like Warp 14, but that The Enterprise D from TNG could only do Warp 9.6 Voyager could do 9.975 and so on. Aparently Gene Roddenbury rearranged the scale from the original 60's series for Next Gen, and so where the eponymous series' Enterprise fits, I have no idea.
But...
I found this online...
According to page 54 of the Star Trek Technical Manual:
Warp 1 = Speed of light
Warp 2 = 10 times the speed of light
Warp 4 = 100 times the speed of light
Warp 8 = 1000 times the speed of light
If you like maths, try here
Or just realise that The Enterprise will either a) arrive just in the nick of time or b) arrive just a moment to late to avert a tragedy, regardless of how warped it's factors are