The rule.
Horizontal drainage slopes at ¼ inch per foot for pipe under 4 inches. At 4" and larger, many codes allow ⅛" per foot with an approved reason.
Free demo · Drain slope
Drain slope calculator.
Run length and pipe size in, required fall out. A quarter inch per foot is the rule everybody knows — this shows the number and where the rule changes. Demo limits apply.
Required fall
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Published code values: ¼"/ft for pipe under 4"; ⅛"/ft is commonly permitted at 4" and larger. Your AHJ is the final word.
Why it matters.
Too flat and solids settle; too steep and water outruns them. The fall is checked on every run of a real isometric — inside the product it snaps automatically.
What stays inside.
The drawing applies slope to every drain run, shows flow direction markers in 3D, and counts hangers at the shop's spacing. The demo does one run at a time.
See it on a drawing
Slope is drawn, not calculated, inside NectARM.
Every drain run carries its fall on the isometric, snaps to shop drain angles, and shows flow markers in the 3D walk.