Pipe Volume Calculator
Find how many gallons a length of pipe holds.
How this calculator works
volume = π × (inside diameter ÷ 24)² × length
Use the inside diameter, not the nominal size. Nominal pipe sizes are a naming convention, not a measurement — 2 inch schedule 40 PVC actually measures 2.049 inches inside, and copper is smaller than its nominal size.
Worked example
With inside diameter 2 in, pipe length 100 ft, this calculator returns 16.32 gal.
Frequently asked questions
How many gallons in 100 feet of 2 inch pipe?
About 16.3 gallons. A 4 inch pipe of the same length holds four times as much at 65 gallons, since volume scales with the square of the diameter.
Should I use nominal or inside diameter?
Inside diameter, always. Nominal pipe size is a naming convention that stopped matching reality decades ago — 2 inch schedule 40 PVC measures 2.049 inches inside, while 2 inch copper type L measures 1.985.
Why does pipe volume matter?
For flushing and chlorinating a new line, for sizing an expansion tank, for working out how long hot water takes to reach a fixture, and for knowing how much a system holds before draining it.
How much does water in a pipe weigh?
Water weighs 8.34 lb per US gallon. A 100 ft run of 4 inch pipe holds 65 gallons — about 545 lb, which matters when hanging pipe from joists.