Pipe Volume Calculator (Metric)
Enter your pipe inside diameter and length to get the volume in cubic feet and gallons.
What your result means
This is the fluid a full pipe holds, figured as a cylinder at 7.48 gallons a cubic foot. Use the inside diameter, not the outside, since the ID is the actual fluid space. For drain capacity, figure a pipe runs about half to two-thirds full, not brimming.
How to use this calculator
- Measure or look up pipe inside diameter.
- Measure pipe length in feet.
- Read cubic feet and gallons of fluid.
- Useful for water volume, drainage capacity.
- Use ID (inner diameter) not OD (outer diameter).
The formula
Convert the diameter to a radius in feet, then the volume is pi times the radius squared times the length. Multiply cubic feet by 7.48 for gallons.
Worked example
Say you've got a 5.1 cm ID pipe 30.5 m long. That's 0.06 m³, or 16.32 gallons.
Pipe water facts
| Item | Value |
|---|---|
| 0.03 m³ | 7.48 gallons |
| Water weight | 8.34 lb/gal |
| Head pressure | 0.433 psi per ft |
| 2.5 cm pipe x 30.5 m | ~4.1 gallons |
Tips & gotchas
- Use the inside diameter, not the outside.
- Nominal pipe sizes are just names; the actual ID varies.
- One cubic foot is 7.48 gallons.
- Water column pressure is 0.433 psi per foot of head.
- For drain pipes, figure half to two-thirds full for capacity.
Frequently asked questions
How much water is in a pipe?
Use the calculator with the pipe ID and length.
Why ID and not OD?
The inside diameter is the actual fluid-carrying space.
How many gallons per 30.5 m of 2.5 cm pipe?
About 4.1 gallons.
Does pipe material affect volume?
Only through the ID. Same nominal size in steel or copper has a similar ID.
How much does the water weigh?
8.34 lbs a gallon, or 62.4 lbs a cubic foot.
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