Pipe Volume Calculator

What Is a Pipe Volume Calculator?

A pipe volume calculator finds how much liquid is held inside a pipe when you give it the inner diameter and the length. It returns the volume in gallons and liters, which is handy for purging lines, dosing chemicals, and estimating the water held in long supply runs. Homeowners use it to figure out how much water sits in a hot water loop or a lawn irrigation line before they drain or flush it.

How It Works

Volume = π × (Diameter ÷ 2 ÷ 12)² × Length. Gallons = Volume × 7.48052. Liters = Volume × 28.3168.

Example

A 3/4 in pipe 20 ft long holds about 0.46 gallons.

How to Calculate

1. Measure or look up the inner diameter of your pipe. For accuracy use the inside diameter, not the nominal label. A 3/4 in PVC pipe has an inner diameter of about 0.82 in.
2. Measure the length of the pipe run in feet. A run from the water heater to a far bathroom might be 40 ft.
3. Enter the diameter and length into the tool. For a 3/4 in pipe 20 ft long it returns about 0.46 gallons.
4. Scale to your actual run. Multiply the per foot volume by your total length. A 3/4 in line holds about 0.023 gallons per foot, so 40 ft holds roughly 0.92 gallons.
5. Use the result to plan purging or dosing. If you need to flush the line, now you know the exact water volume you are moving.

Approximate water volume per 100 feet of pipe

Sources

• International Plumbing Code (IPC)
• American Society of Mechanical Engineers (ASME)
• American Water Works Association (AWWA)

Frequently Asked Questions