Drain & vent pipe size by fixture units

Drains and vents are sized by drainage fixture units (DFU): the more DFU a branch carries, the larger the required pipe. The table shows a minimum drain size and a minimum vent size by DFU as labeled planning bands — building drains, stacks, slope and developed length change the allowance, and your local plumbing code governs. Use them with the drain pipe size and vent size tools.