Pipe Volume Calculator (Gallons in a Pipe)
Enter the pipe’s inside diameter and length to get the volume of water it holds in gallons, cubic feet, and liters — handy for flushing, chlorination dosing, and pressure-test volumes. The math updates as you type.
Pipe Volume Calculator
Enter inside diameter in inches and length in feet.
Uses inside diameter, not nominal pipe size — actual inside diameter varies by pipe schedule and material. Estimates only; confirm with pipe spec sheets for chlorination or pressure-test dosing.
How the pipe volume formula works
A pipe is a cylinder, so its volume is π × radius² × length. Convert the inside diameter to a radius in feet, multiply by length in feet to get cubic feet, then convert to gallons (1 ft³ = 7.48052 gallons) or liters (1 gallon = 3.78541 liters).
| Step | Example: 2 in inside diameter, 100 ft long |
|---|---|
| Radius in feet | (2 ÷ 2) ÷ 12 = 0.0833 ft |
| Volume in cubic feet | π × 0.0833² × 100 = 2.18 ft³ |
| Gallons | 2.18 × 7.48052 = 16.32 gallons |
| Liters | 16.32 × 3.78541 = 61.78 liters |
For chlorination or disinfection dosing, this volume tells you exactly how much water is in the run so you can calculate the correct chemical concentration. For pressure testing, it tells you how much water (or air) you are working with before you charge the line.
Contractor Estimate Calculator (Excel & Google Sheets)
Turn quantities into a priced, itemized estimate — materials, labor, markup, and profit, auto-totaled. The estimate you hand the client after the calculator tells you the numbers.
Common uses on the job
Plumbers use pipe volume most often for flushing new lines (knowing how many gallons must pass through before water runs clean), chlorination of potable water mains (dosing chemical to a known volume of water), and hydrostatic pressure testing (knowing how much water fills the test section). Always use the actual inside diameter for the pipe schedule and material in use — nominal size and inside diameter are not the same thing.
Once the volume is known, send a clean invoice
The calculator gives you the volume; your bid turns it into a price. When the job is done, bill it with an itemized plumbing invoice that separates materials, labor, and testing — so your margin is in the number before the job wraps.
Frequently asked questions
Does nominal pipe size equal inside diameter?
No. Nominal pipe size is a naming convention, not a measurement. Actual inside diameter varies by pipe schedule, wall thickness, and material, so always check the manufacturer spec sheet for the exact inside diameter before dosing or pressure-test calculations.
How many gallons are in 100 feet of 2-inch pipe?
Using a 2-inch inside diameter, 100 feet of pipe holds about 16.3 gallons. The exact figure depends on the true inside diameter of the pipe in use.
Why does chlorination need the pipe volume?
Disinfection dosing is calculated as a chemical concentration per volume of water. Knowing the exact gallons in the pipe run lets you dose to the correct parts-per-million rather than guessing.
Is this pipe volume calculator free?
Yes — free, no sign-up. Enter inside diameter and length and read the gallons, cubic feet, and liters. Estimates only; confirm with pipe spec sheets.