Calculators / Pipe Volume
Pipe Volume calculator
Distribution exams ask for pipe volume when you disinfect a new main, flush a line or figure out a dose. Convert the diameter to feet first, then use 0.785 × D² × length × 7.48.
Volume (gal) = 0.785 × (D in ÷ 12)² × Length (ft) × 7.48
Worked example
A new 12-inch water main is 1,000 ft long. How many gallons does it hold?
- Diameter = 12 in ÷ 12 = 1 ft
- Area = 0.785 × 1² = 0.785 ft²
- Volume = 0.785 × 1,000 × 7.48 = 5,871.8 gal
Answer: 5,871.8 gal
Common mistakes
- Leaving the diameter in inches. Divide by 12 first.
- Forgetting 7.48 and answering in cubic feet.
Check your exam's reference sheet for its exact constants. Some use 3.14 instead of 3.1416, which changes answers in the last digit.