Not a definitive source, but the Marvel Wiki estimates a range of 60 feet.
The web line's tensile strength has been estimated to be 120 pounds
per square millimeter of cross section. The 300 p.s.i. pressure in
each cartridge is sufficient to force a stream of the complex web
pattern an estimated 60 feet. (It goes significantly farther if
Spider-Man shoots it in a ballistic parabolic arc.)
There's plenty of room for argument here, but it's a base to to start from. That doesn't allow for wind, elevation, or any other number of factors either.
One could be cynical and say that it fires as long (or as short) as the plot demands.