Pipe Volume Calculator
Gallons, liters & flow per pipe size
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Formula & explanation
The pipe is treated as a cylinder: cross-sectional area (π × radius²) times length gives cubic feet. Multiply by 7.48 to get US gallons. This is the static fill volume — useful for sizing pumps, estimating drain-down, or planning thermal storage. Flow rate is a separate calculation depending on pressure and pipe roughness.
Example calculation
100 ft of 1\" pipe:
Radius = 0.0417 ft. Area = π × 0.00174 = 0.00545 sq ft × 100 ft = 0.545 cu ft × 7.48 = 4.08 gallons of water.
Buying & project-planning tips
- Nominal pipe size isn't the actual inside diameter — check pipe schedule (SCH 40 vs 80) for precision.
- Use this to estimate how much water drains when you shut off supply for repairs.
- For heating systems, water volume determines expansion-tank sizing — consult your boiler manual.
- Long horizontal runs hold more water than expected — plan drainage for freeze protection.
- Flow rate (GPM) depends on pressure, not just volume — see the water pressure calculator.
Frequently asked questions
Is nominal pipe size the actual inside diameter?+
No — nominal sizes are historical labels. A 1" SCH 40 pipe has an actual inside diameter of about 1.05", while a 1" SCH 80 is about 0.95". Verify the actual ID for precise volume.
How do I convert pipe volume to flow rate?+
Volume × frequency of fill = flow rate. For continuous flow, GPM depends on pressure and pipe friction — use the water pressure calculator or a flow-rate chart for your pipe material and size.
Why calculate pipe water volume?+
To size expansion tanks in heating systems, estimate how much water drains during repairs, plan freeze protection, or size a pump for a known pipe fill.
Does pipe material affect volume?+
Only through wall thickness (which changes actual ID). A 1" copper, PVC, or steel pipe each hold slightly different volumes at the same nominal size.