Drain Slope
Verify a drain pipe's slope against the required fall.
About Drain Slope
Slope is the total fall divided by the pipe length, giving inches of drop per foot. Comparing it to the required slope confirms the drain will flow. Gravity drains need a minimum slope to keep waste moving, and too little fall causes clogs and standing water.
Formula
Drain Slope
Slope = total drop / pipe length
- required slope
- Commonly 1/4 inch per foot
Worked example
With the default values below, Drain Slope returns Actual Slope of 0.125. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Pipe length
- 20 ft
- Total drop
- 2.5 in
- Required slopeminimum 0 in/ft
- 0.25 in/ft
Results
- Actual Slope
- 0.125 in/ft
- Percent Slope
- 1.04%
- Drop Needed
- 5.00 in
- Slope Check
- Below the required slope
Step by step
- 1Values used
- 2Drain Slope
- 3Actual Slope= 0.125 in/ft
- 4Percent Slope= 1.04
- 5Drop Needed= 5.00 in
- 6Slope Check= Below the required slope
Assumptions and limits
- The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Drain Slope calculated?
Slope = total drop / pipe length Slope is the total fall divided by the pipe length, giving inches of drop per foot. Comparing it to the required slope confirms the drain will flow.
Why does Drain Slope matter?
Gravity drains need a minimum slope to keep waste moving, and too little fall causes clogs and standing water.
What values do I need to enter?
This calculator takes 3 inputs: Pipe length, Total drop, Required slope. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.