Pipe Volume Calculator
Gallons, cubic feet, and liters of water inside a pipe run for any diameter and length.
- Volume (gallons)
- 65.28
- Volume (cubic feet)
- 8.727
- Volume (liters)
- 247.11
- Per 100 ft
- 65.28 gal
Why pipe volume matters
Pipe volume shows up any time you have to fill, flush, disinfect, or pressure test a pipe run. A new water service line has to be chlorinated and flushed to code, which requires knowing how many gallons of chlorine solution to prepare and how many gallons of clean water to push through afterward.
For pressure testing, volume tells you how much water it takes to charge the line and how much air might be trapped. For irrigation supply lines and pool circulation, volume determines flush time and dose calculations for shock treatments.
The formula from geometry
Pipe volume is a cylinder: pi times radius squared times length. The math is easy; unit conversion is where mistakes happen. Radius in feet times radius in feet times length in feet gives cubic feet. Multiply by 7.48 to get US gallons.
Worked example: a 4 inch inside diameter pipe running 100 feet. Radius is 2 inches, or 0.167 feet. Volume is π x 0.167 x 0.167 x 100 = 8.73 cubic feet, or 65.3 gallons. A 6 inch pipe of the same length holds 146.9 gallons; a 2 inch pipe holds 16.3 gallons.
Common pipe capacities per 100 ft
1/2 inch ID: 1.0 gallons per 100 ft.
3/4 inch ID: 2.3 gallons per 100 ft.
1 inch ID: 4.1 gallons per 100 ft.
1.5 inch ID: 9.2 gallons per 100 ft.
2 inch ID: 16.3 gallons per 100 ft.
3 inch ID: 36.7 gallons per 100 ft.
4 inch ID: 65.3 gallons per 100 ft.
6 inch ID: 146.9 gallons per 100 ft.
Inside diameter vs nominal size
Pipe is labeled by nominal size, not actual inside diameter. Schedule 40 PVC has different wall thickness than Schedule 80 or CPVC, so the inside diameter differs slightly. For water volume calculations, use the actual ID from the manufacturer specification.
For rough estimates, nominal size is close enough to ID for pipes 2 inch and larger. For smaller pipes, especially copper types L and M, the wall thickness difference matters. Copper type L 3/4 inch has an ID of about 0.785 inches; copper type M 3/4 inch has an ID of about 0.811 inches. Not enough to change a flush volume, but enough to affect flow calculations.
For plumbing and irrigation contractors
Volume math shows up every day in service work. Peak Local Leads builds and ranks local plumbing and irrigation sites for one contractor per Texas market. Seven days of calls to prove it, flat monthly after.
Frequently asked.
- How many gallons in a 100 ft run of 1 inch pipe?
- About 4.1 gallons. Multiply by pipe run length in hundreds of feet for total volume.
- How do I calculate pipe volume in gallons?
- Volume in cubic feet equals pi times (radius in feet)² times length. Multiply cubic feet by 7.48 to get US gallons.
- What is the volume of a 4 inch pipe?
- A 4 inch ID pipe holds about 65.3 gallons per 100 feet, or 0.653 gallons per foot.
- Does pipe material affect volume?
- Only through inside diameter. PVC, copper, PEX, and steel all hold the same volume of water at the same ID, but different materials have different ID at the same nominal size due to wall thickness.
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