Drain Pipe Slope Calculator
Estimate minimum drain pipe slope, grade, and total pipe drop based on pipe diameter and length.
Choose a pipe diameter group and enter the pipe length. Results update automatically as you change your measurements.
Minimum Drain Pipe Slope
Total drop is calculated using the minimum slope for the selected diameter group.
How to Use the Calculator
- Select SI / Metric or US / Imperial units.
- Choose the pipe diameter group that matches your drain pipe and locally adopted plumbing code.
- Enter the total horizontal pipe length. Results update automatically.
- Use Reset Calculator to restore the default settings.
Assumptions and Limitations
This calculator uses common minimum horizontal drainage slopes associated with IPC Table 704.1: 1/4 inch per foot for pipe sizes 2.5 inches or smaller, 1/8 inch per foot for 3–6 inch pipe, and 1/16 inch per foot for pipe 8 inches or larger. These are reference values, not a guarantee of local code compliance. The listed groups do not cover every possible nominal pipe size; verify the applicable requirement and locally adopted plumbing code before installation. The calculator estimates slope and elevation drop only; it does not size pipe capacity or account for fittings, flow, or site-specific conditions.
