What it calculates
Calculate water volume inside a pipe run.
Pipe Volume Calculator
Calculate gallons contained in a round pipe run.
Planning and estimating aid only. Verify project requirements, manufacturer instructions, adopted codes, permits, and field conditions before performing regulated work.
Plumbing planning
How to Use This Calculator
Use the field units shown below, then compare your result with the worked example. This is a capacity calculation, not a flow-rate or pressure-loss calculation.
How the calculation works
The pipe is treated as a cylinder. Internal cross-sectional area is multiplied by pipe length, then cubic inches are converted to gallons.
What the result means
Use actual inside diameter rather than nominal pipe size when accuracy matters.
Use internal diameter for the water-holding volume
With an internal diameter of 1 inch and length of 100 feet, cross-sectional area is π × 0.5² square inches. Multiply by 1,200 inches of length and divide by 231 cubic inches per U.S. gallon to obtain about 4.08 gallons.
Contractor tip: This is a capacity calculation, not a flow-rate or pressure-loss calculation. Two pipes with the same holding volume can have very different hydraulic behavior.
Verify the final quantity
Use actual inside diameter, not outside diameter or nominal pipe size. The model represents a straight cylindrical volume and does not add water held in fittings, tanks or equipment.
Good practice: Compare the calculated quantity with plans, specifications, product packaging and current field conditions before purchasing material.