Drain Slope Calculator

About the Drain Slope Calculator

Calculates the vertical fall a drain pipe needs over its horizontal run for a given slope, and the resulting slope percentage.

How to use this calculator

1. Enter the slope in a usable form, such as a decimal, percent, or ratio if the calculator supports it.
2. Enter the pipe length or run.
3. Read the fall, which is the vertical drop over that distance.
4. Check that your units match, for example meters, feet, or inches.

The formula explained

The formula \(fall = slope \times length\) computes the vertical drop of the drain pipe from its slope and horizontal run. It tells you how far the pipe falls over the given length.

• fall = the vertical drop of the drain pipe
• slope = the gradient of the pipe, written as a decimal, percent, or ratio converted to a decimal
• length = the horizontal run or pipe length

Step by step method

1. Write the slope as a decimal if needed. For example, a slope of \(2\\%\) becomes \(0.02\).
2. Multiply \(slope\) by \(length\) to find the fall.
3. Keep the units consistent, so the answer is in the same unit as the length.
4. If needed, convert the result back into inches, feet, meters, or centimeters.

Worked example

Problem. A drain pipe is \(12\\,\\text{m}\) long and has a slope of \(0.5\\%\). What is the fall?

1. Convert the slope to a decimal, \(0.5\\% = 0.005\).
2. Use the formula \(fall = slope \\times length\). So, \(fall = 0.005 \\times 12\).
3. Calculate \(fall = 0.06\\,\\text{m}\).

Tips and common mistakes

• Make sure you use the same unit for the length and the final drop, because mixing feet and inches can lead to mistakes.
• If your slope is given as \(1\\!:\\!100\), convert it to \(0.01\) before multiplying.

Frequently asked questions