Pipe Volume Calculator

How the pipe volume calculator works

A pipe is a long cylinder, so its volume is the area of the circular opening times the length. Enter the inside diameter in inches and the length in feet. The calculator converts the diameter to a radius in feet, finds the volume in cubic feet, then converts to U.S. gallons and liters.

Use the inside diameter, not the nominal size. A pipe sold as 4 inch nominal can have an inside diameter that differs by schedule or wall thickness, so check the maker’s data. Inside diameter is the number that matters for how much liquid the pipe holds.

The formulas

There are 1,728 cubic inches in a cubic foot and 231 cubic inches in a U.S. gallon, which gives 7.480519 gallons per cubic foot. See the NIST conversion factors.

Example: A pipe with a 4 inch inside diameter and a length of 100 feet holds 65.28 gallons, which is 8.727 cubic feet or 247.1 liters. Per foot of pipe that is 0.653 gal/ft. These sizes are an illustration only.

Uses and limits

Typical uses are estimating the water that will drain out of a line, the amount of fluid needed to fill a new run, or how much chemical to dose a pipe. Fittings, valves, elbows and tees add volume that is not counted here, and a pipe that is partly full holds less. For a total run with several diameters, calculate each section and add the results.

The figure is a geometric capacity of the bore. It does not include flow rate or pressure loss, which depend on other factors. To work out volume for a large round or box-shaped container, use the pool volume calculator or the cubic yard calculator.

Finding the inside diameter

Pipe is sold by nominal size, and the true bore depends on the material and the wall thickness. Thicker walls mean a smaller bore. Look up the inside diameter for your material and schedule in the manufacturer’s data sheet, or measure the bore across the open end of a cut piece with calipers or a ruler.

Handling a run with several sizes

If a line steps down from one diameter to another, calculate each section on its own and add the gallons. The same method works for bends and long curves: use the developed length along the centerline of the pipe. Short fittings are small compared with the pipe itself, but on short runs with many fittings the extra volume can matter, so add an allowance.

Remember that gallons here are U.S. liquid gallons. If you have a result in cubic feet and need gallons, multiply by 7.48. To go from gallons to cubic feet, divide by 7.48. Liters are shown for metric work. The gallons per foot figure is handy for quick checks: multiply it by any length of the same pipe to get the capacity.

Frequently asked questions

More free tools: All free calculators · Pool volume calculator · Cubic yard calculator