Water gallons · air cubic feet · multi-segment · dry system reference
Quick Single Pipe
Multi-Segment Pipe Run Builder
Add multiple pipe segments to calculate total system volume. Useful for dry system air volume, drain-down estimates, and fill calculations.
Single Pipe Results
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Quick reference for common pipe sizes at Schedule 10 and Schedule 40. Values based on nominal internal diameters per ASME B36.10M.
| NPS | Sch 10 ID | Sch 10 Gal/ft | Sch 10 ft³/ft | Sch 40 ID | Sch 40 Gal/ft | Sch 40 ft³/ft |
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This calculator computes the internal volume of steel pipe in both water gallons and air cubic feet. It is designed for fire protection professionals who need volume data for system fill estimates, drain-down planning, dry system air volume calculations, nitrogen fill estimates, and antifreeze quantity planning.
Water volume (gallons) is the amount of water a pipe holds when completely filled. Air volume (cubic feet) is the internal volume of the pipe when empty — this is the volume that must be pressurized in dry and preaction systems. The relationship is simple: 1 gallon = 0.1337 ft³, or 1 ft³ = 7.481 gallons.
Dry sprinkler systems and preaction systems contain pressurized air or nitrogen in the piping above the dry valve or preaction valve. The total air volume in the system determines compressor sizing, trip time (time from valve activation to water delivery at the most remote sprinkler), and nitrogen generator capacity.
NFPA 13 limits the maximum time for water to reach the inspector's test connection to 60 seconds for most dry systems. Larger air volumes require larger valve sizes or faster air release to meet this requirement. Nitrogen inerting (replacing air with nitrogen) reduces internal corrosion in dry and preaction systems and is increasingly specified for system longevity.
When calculating nitrogen fill volume, use the total pipe air volume at the supervisory pressure (typically 40 PSI). The actual nitrogen quantity (in standard cubic feet or SCF) must account for the gauge pressure using Boyle's Law: SCF = pipe volume (ft³) × (gauge PSI + 14.7) / 14.7.
It varies widely based on system size and pipe diameters. A small system with 100 feet of 2″ pipe holds about 17 gallons. A large system with 500 feet of mixed 4″ and 6″ mains plus branches could hold 300+ gallons. Use the multi-segment builder to estimate your specific system.
When a sprinkler opens on a dry system, pressurized air must exhaust before water can reach the sprinkler. Larger air volumes mean longer delivery times. NFPA 13 limits this to 60 seconds for most systems. Knowing the air volume helps size the dry valve, quick-opening devices, and accelerators.
First calculate the total pipe volume in cubic feet using this tool. Then apply Boyle's Law: nitrogen quantity (SCF at atmospheric) = pipe volume (ft³) × (supervisory pressure + 14.7) / 14.7. For example, 50 ft³ of pipe at 40 PSI gauge needs 50 × 54.7/14.7 = 186 SCF of nitrogen.
No. This calculator computes volume for straight pipe segments only. Fittings, sprinkler drops, riser nipples, and branch line tees add small additional volumes. For most estimates, the straight pipe volume is sufficient. For precise dry system trip time calculations, include all components.
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