Pipe Volume Calculator
A pipe is just a long cylinder: V = πr²L using the inner diameter. Enter the ID in inches and the run length in feet to get gallons and the water’s weight.
Example: with Inner diameter (in) 1 · Pipe length (ft) 50 → Pipe volume: 2.04 gallons.
Computed by the calculator below using its default values. Change any input to see your own numbers.
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Check it outPipe volume in gallons, per foot and per run
Volume of a pipe = π × (ID ÷ 2)² × length. Work in inches (length × 12), then divide by 231 to get gallons. The default 1-inch ID line running 50 ft holds π × 0.5² × 600 ≈ 471.24 in³ = 2.04 gallons — about 17.0 lb of water.
Handy per-foot figures: a ½-in ID pipe holds 0.0102 gal per foot, ¾-in holds 0.0229, 1-in holds 0.0408, and 2-in holds 0.1632 gal per foot. Use the actual inner diameter, not the nominal trade size — “¾-inch” type L copper actually has a 0.785 in ID, and schedule-40 PVC runs different again. That gap matters when you’re sizing a recirculation loop, estimating how much antifreeze to displace, or figuring how long the hot water takes to arrive.
How it’s calculated
Volume = π × (inner diameter ÷ 2)² × (length × 12), all in inches, giving cubic inches. Gallons = in³ ÷ 231 (a US gallon is exactly 231 in³, NIST Handbook 44); cubic feet = in³ ÷ 1,728. Water weight uses 8.345 lb per gallon (maximum-density water, USGS).
Results update as you type and are estimates, not professional advice — verify important decisions with a qualified professional.
Common mistakes
- Using the nominal pipe size or outer diameter — capacity depends on the actual inner diameter, which varies by material and schedule.
- Forgetting to convert the run length from feet to inches (× 12) when doing the math by hand.
- Measuring a coiled or sloped run short — volume follows the full pipe length, not the straight-line distance.
Frequently asked questions
How do I find the volume of a pipe in gallons?
Multiply π × (inner diameter ÷ 2)² × length in inches, then divide by 231. A 1-in ID pipe 50 ft long: π × 0.25 × 600 ≈ 471.24 in³ = 2.04 gallons.
Do I use the inner or outer diameter?
Inner. Water fills only the bore, and wall thickness varies — nominal ¾-in copper type L has a 0.785 in ID, while the OD is 0.875 in. Measure or look up the true ID for your material.
How much does the water in a pipe weigh?
Multiply gallons by 8.345 lb (cold water at maximum density). The 2.04 gallons in the default 50 ft run weighs about 17 lb — worth knowing before pressure-testing overhead runs.
How many gallons per foot does a 2-inch pipe hold?
About 0.1632 gallons per foot of true 2-in ID. Multiply by the run length: 100 ft of 2-in pipe holds 16.32 gallons.