Vent Pipe Size Calculator

A drain needs to breathe. Every fixture that discharges pushes air ahead of it and sucks air behind it; the vent keeps the pressure balanced so traps stay sealed and solids keep moving.

Vent Pipe Size Calculator gives a preliminary vent size from your connected fixture units and vent length, using typical IPC-style capacity tables.

• DFU in, vent out: minimum vent size for the load.
• Length aware: longer vents step up in size.
• Context: individual and common vent modes.
• Capacity shown: the DFU/length the size covers.
• Export: Copy or download the report.

1. Total the connected fixture units on the vent.
2. Enter the vent length to the stack or open air.
3. Choose the vent type - individual or common.
4. Read the minimum vent size and its limits.

Example - Bathroom group. Toilet 3 + shower 2 + lav 1 = 6 DFU on a 20 ft vent. The table suggests 2 in comfortably; a 1.5 in works for the lav but the shared vent for the group should follow the heaviest fixture rule.

• Plan the vent core early: sizes before the wall closes.
• Common or individual: both normal cases covered.
• Pairs with DFU tools: reuse the fixture unit total.
• Free and private: no uploads, no logging.