How far can a drainpipe go before it reaches the vent stack ?

A 1 1/2"drain line can go 3 1/2'.
A 2" " " " " 5'
A 3" " " " " 6'
A 4" " 6'
A 4" " " 10

UPC measured from the weir of the trap to the vent opening.
Other codes can very but UPC's about average. Cheers, Tom