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Plumbing & Piping

Drain Pipe Slope Calculator — Fall per Foot

Inputs

1200
0.524

Smart analysis

Recommendations

Tailored to your live inputs and result—guidance only, not professional advice.

  • Interpret

    Treat this as a planning estimate

    Primary result: Slope = 2.08%. Re-run with optimistic and pessimistic inputs to understand the range—not just a single point.

Scenario studio

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Scenario A

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Plain-English guide

Terms & how it works

Confused by a field? Read the short definitions here while you use the tool.

  • Horizontal run (ft)

    The “Horizontal run (ft)” value used in this tool’s formula. Adjust it to see results update live.

  • Vertical drop (in)

    The “Vertical drop (in)” value used in this tool’s formula. Adjust it to see results update live.

Slope % = (drop ÷ run) × 100; fall per foot = drop ÷ run.

Compute drain grade from horizontal run and vertical drop. Planning estimates only — verify measurements and local codes on site.

How this calculator works

Compute drain grade from horizontal run and vertical drop. Planning estimates only — verify measurements and local codes on site. Slope % = (drop ÷ run) × 100; fall per foot = drop ÷ run. Scenario: 20 ft run with 5 in drop → 2.08% slope, 0.25 in/ft fall.

Slope % = (drop ÷ run) × 100; fall per foot = drop ÷ run.

Scenario: 20 ft run with 5 in drop → 2.08% slope, 0.25 in/ft fall.

When to use this Drain Slope

Common use cases

  • Compute drain grade from horizontal run and vertical drop.
  • Sanity-check with this scenario: 20 ft run with 5 in drop → 2.08% slope, 0.25 in/ft fall.
  • The relationship is: Slope % = (drop ÷ run) × 100; fall per foot = drop ÷ run.

Localized examples

  • Plumbing & Piping: the example on this page uses the same formula as the widget.

What you get

  • Fields: Horizontal run (ft), Vertical drop (in)
  • Slope % = (drop ÷ run) × 100; fall per foot = drop ÷ run.
  • Scenario on the page: 20 ft run with 5 in drop → 2.08% slope, 0.25 in/ft fall.

How to Calculate Drain Slope

  1. 1Enter Horizontal run (ft), Vertical drop (in). Use the values you have, not a catalog average, unless that is all you know.
  2. 2Slope % = (drop ÷ run) × 100; fall per foot = drop ÷ run.
  3. 3Scenario: 20 ft run with 5 in drop → 2.08% slope, 0.25 in/ft fall.
  4. 4Buy materials after you walk the job. This is a first-pass quantity, not a purchase order.

Governing formula

Slope % = (drop ÷ run) × 100; fall per foot = drop ÷ run.

20 ft run with 5 in drop → 2.08% slope, 0.25 in/ft fall.

20 ft run with 5 in drop → 2.08% slope, 0.25 in/ft fall.

Variable definitions

  • runLengthFt

    Horizontal run (ft)

    The “Horizontal run (ft)” field. Default 20; typical range 1–200.

  • dropIn

    Vertical drop (in)

    The “Vertical drop (in)” field. Default 5; typical range 0.5–24.

  • The takeoff (Slope % = (drop ÷ run) × 100; fall per foot = drop ÷ run.) ignores waste, code, and what you find when you open the wall. Measure twice on site.
  • Nothing here is uploaded for the calculation itself.

Frequently Asked Questions

Slope % = (drop ÷ run) × 100; fall per foot = drop ÷ run.

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Community

Reviews & Ratings

See what others think about this tool, then leave your own rating to help improve CalculioHub.

4.8

out of 5.0

4 reviews

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Your rating

Aisha K.

Mar 12, 2026

Clean layout and the results update instantly. Exactly what I needed for a quick planning check.

Daniel R.

Feb 28, 2026

Very usable on mobile. Would love a save/export option later, but the math feels solid.

Priya S.

Feb 3, 2026

The FAQ section answered my questions before I even had to search. Smooth dark mode too.

Marcus L.

Jan 19, 2026

Simple inputs, clear outputs. This replaced three bookmarks I used to juggle.

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