Get the recommended drainage slope based on pipe diameter and calculate the required fall.
How to Use the Drainage Pipe Slope Calculator
Select your pipe's "Pipe Diameter" category.
Enter the "Pipe Length (m)".
Click "Calculate" to see the recommended slope and required fall.
Frequently Asked Questions
Smaller-diameter drain pipes (up to 3 inch) need a steeper slope (around 2%) to keep flow velocity high enough to carry solids, while larger pipes (4-6 inch and above) can use a gentler slope (around 1% or less) because they already have more flow capacity.
They reflect common plumbing code guidance (such as the widely referenced 1/4 inch per foot for smaller pipes and 1/8 inch per foot for larger pipes). Always check your local building code, since exact minimums vary by jurisdiction.
Yes, a steeper slope is usually acceptable and often improves drainage, as long as it doesn't create installation/depth issues. Going below the recommended minimum is what typically causes problems.
Yes, it's completely free and requires no sign-up.