Plumbing Fall Calculator
Calculate minimum pipe fall and grade per run length for drainage compliance.
Estimate only — not a substitute for a licensed tradesperson, a certified engineer, or sign-off from your local building surveyor. Verify against current standards and site conditions before ordering materials or starting work.
Result
- Total fall over run
- 100mm
CORRECTED 2026-08-31. The previous note described 1:100 as the 'commonly-cited' minimum sanitary drain fall - that was never verified against AS/NZS 3500.2 and should not have read as though it had been. The minimum grade depends on pipe size and application, and comes from AS/NZS 3500.2, which is a licensed standard whose tables are deliberately not reproduced here. This calculator converts a fall ratio YOU supply into a total fall over the run - it does not tell you which ratio is correct for your pipe. Get that from AS/NZS 3500.2 or your plumber.
What this is based on
Governed by AS/NZS 3500.2 (Sanitary plumbing and drainage). The minimum grade depends on pipe size and application and comes from that standard's tables, which are a licensed compilation and are deliberately NOT encoded here. This calculator converts a fall ratio you supply into a total fall - it does not tell you which ratio is correct for your pipe.
We cite the clause and link to the publisher so you can read the source yourself. We do not reproduce the text or tables of the NCC or of any Australian Standard.