Pipe Volume Calculator
A pipe's volume is π × (inside diameter ÷ 2)² × length; multiply cubic feet by 7.48 for US gallons. A 4 in bore, 100 ft long, holds 8.72 ft³ — about 65.2 gallons running full. Use the actual inside diameter, not the nominal size, because volume changes with its square. For tanks, use the Tank Volume Calculator.
How it's calculated: Volume = π × (inside diameter ÷ 2)² × length; 1 ft³ ≈ 7.48 US gallons, 1 m³ = 1,000 L.
Result appears here
Fill in the fields and press Calculate.
Formula, calculation, assumptions and sources
V = π × (Inside diameter ÷ 2)² × Length
1 ft³ ≈ 7.48 US gallons; 1 m³ = 1,000 L
Run the calculation to see each step with your own numbers.
A 4 in ID pipe, 100 ft long, running full.
Cross-section = π × (2 in)² = 12.57 in²
Volume = 12.57 in² × 1,200 in = 15,080 in³ = 8.72 ft³
≈ 65.2 US gallons
- The pipe runs full. For a partly full gravity line, this is the maximum.
- Use the actual inside diameter — nominal pipe sizes differ from the bore, and the difference matters for volume (it's squared).
- Fittings, valves and the small taper at joints are ignored.
- Nominal size or actual bore?
- Actual bore (inside diameter). A 'nominal 2-inch' pipe can have an ID anywhere from about 1.9 to 2.1 in depending on material and schedule, and volume changes with the square of that.
- How do I find the inside diameter?
- From a pipe-dimension table for your material and schedule. A nominal 4-in Schedule-40 PVC pipe has an ID close to 4.0 in; the same nominal size in Schedule-80 or in copper is smaller.
- What if the pipe isn't running full?
- This gives the full capacity, which is the maximum. A gravity drain line typically runs part-full — estimate the fraction of the cross-section that is wetted and scale the result down.
- How many gallons are in 100 feet of 4 inch pipe?
- About 65 US gallons for a 4 in inside diameter running full: π × (2 in)² × 1,200 in = 15,080 in³, or 8.72 ft³. A pipe with a smaller actual bore holds less.
- How do you calculate the volume of water in a pipe?
- Square half the inside diameter, multiply by π and by the length, keeping the units consistent. Convert cubic feet to US gallons by multiplying by about 7.48, or cubic metres to litres by multiplying by 1,000.
Geometry
Cylinder volume. Unit conversions per NIST SP 811 (1 US gallon = 3.785411784 L exactly).
About the Pipe Volume Calculator
The Pipe Volume Calculator gives how much liquid a full length of pipe holds, from the inside diameter (the bore, not the nominal size) and the length. Volume changes with the square of the diameter, so getting the bore right matters. For the weight of the pipe itself rather than its contents, use the Pipe Weight Calculator.
What you enter
- Inside diameter — The bore, not the nominal size — a nominal 4-in Schedule-40 PVC pipe is about 4.0 in ID.
- Pipe length
What you get back
- Liquid volume — the exact result of the calculation.
- Volume — the exact result of the calculation.
The formula, a worked example, the assumptions behind it and the sources are shown in full below the calculator.
Related calculators
- Tank Volume Calculator — Capacity of a tank — cylindrical, rectangular or oval — full or partly filled.
- Pipe Weight Calculator — Weight of a length of pipe from its size, wall thickness and material.
- Pond Calculator — Volume of a pond and the liner size it needs.
Part of the Water & Volume calculators.