Pipe and fitting volume sketches show up when you are estimating water in a sprinkler branch, a test header, or a short supply segment. The geometric volume of a circular pipe is V = π(d/2)²L with diameter and length in consistent units. This page explains that sketch and gives a free browser calculator that accepts internal diameter (inches) and length (feet), then reports volume in cubic feet and U.S. gallons (ft³ × 7.4805 for freshwater). It is for learning and quick checks—not a substitute for manufacturer data, the criteria adopted by your authority having jurisdiction, or review by a licensed design professional.
How pipe volume is used
- Enter the actual internal diameter (ID), not the nominal trade size. Schedule and material change ID for the same nominal size (for example Schedule 40 vs Schedule 10 steel).
- Enter the developed length of the segment in feet (include fittings only if you are intentionally approximating their volume separately).
- Compute V = π(d/2)²L with d and L converted to the same unit system (here: inches → feet for the diameter).
- Convert ft³ to gallons with the freshwater factor 7.4805 gal/ft³ when you need a gallon sketch.
- Treat the result as geometry only. It does not size pumps, confirm listing data, or replace hydraulic calculations in the adopted edition.
Free calculator
Educational approximation only. Freshwater gallons = ft³ × 7.4805. Nothing you enter leaves your browser. For velocity sketches see the sprinkler pipe velocity calculator; for orifice flow see the orifice flow calculator; for pressure/head see PSI to feet of head. Full segment friction tables live in the Sprinkler Pipe Friction Loss workbook.
Worked example
A 100 ft segment of pipe with an actual internal diameter of 2.067 in (a common Schedule 40 steel ID near 2 in nominal): d = 2.067/12 ≈ 0.1723 ft, V = π(0.1723/2)²×100 ≈ 2.33 ft³ ≈ 17.4 gallons. Change the ID or length and the sketch moves with them. Always confirm the published ID for the exact schedule and material you are modeling, and check the result against the adopted edition, manufacturer data, and AHJ.
Next steps: estimate velocity with the free sprinkler pipe velocity calculator, sketch orifice flow with the orifice flow calculator, convert pressure and head with PSI to feet of head, and run full segment friction tables in the Sprinkler Pipe Friction Loss workbook ($29).