Free Plumbing Tool
Pipe Volume Calculator
Enter pipe size and length to instantly get volume in gallons, cubic feet, and liters. Add an optional flow rate to calculate fill time. Includes a full Schedule 40 pipe volume reference table.
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Calculate Pipe Volume
Select a Schedule 40 pipe size or enter a custom inner diameter. Add length and an optional flow rate for fill time. Results update instantly.
Based on Schedule 40 inner diameter. Use “Enter inner diameter” for other schedules.
Enables fill time calculation.
Volume results
Gallons (US)
17.43
Cubic feet
2.33
Liters
65.99
Fill time
Enter GPM above
Inner diameter used
2.067"
Gallons per foot
0.1743
Cubic inches total
4,026.7
Schedule 40 Pipe Volume Reference Table
Gallons and liters per linear foot for standard Schedule 40 pipe sizes. Use these values to quickly estimate system volume without entering each run individually.
Why does pipe volume matter on the job?
Pipe volume drives several critical decisions: sizing expansion tanks for hydronic systems, calculating glycol and chemical treatment doses, pressure-testing line segments, and estimating fill and flush times for commissioning.
For glycol-filled systems, the industry rule of thumb is to move at least two full pipe volumes during a flush to fully remove the old fluid. Underestimating volume means undertreated or inadequately flushed systems — and callbacks.
Schedule 40 vs Schedule 80: volume difference
Schedule 80 pipe has thicker walls and a smaller inner diameter than Schedule 40 of the same nominal size. A nominal 2“ Schedule 80 pipe has an ID of 1.939“ vs 2.067“ for Schedule 40 — about 12% less volume per foot.
For accurate results on Schedule 80 or other non-standard schedules, switch to “Enter inner diameter” mode above and type in the actual ID from the pipe spec sheet or manufacturer data.
How Much Water Is in a Pipe? Quick Examples
These are the pipe volumes contractors look up most often, calculated for full Schedule 40 pipe. Need a different size, length, or schedule? Enter it in the calculator above for an exact answer.
1/2" pipe, 100 ft
≈ 1.6 gallons
3/4" pipe, 100 ft
≈ 2.8 gallons
1" pipe, 100 ft
≈ 4.5 gallons
2" pipe, 100 ft
≈ 17.4 gallons
4" pipe, 100 ft
≈ 66 gallons
6" pipe, 100 ft
≈ 150 gallons
Working in metric? The calculator accepts any inner diameter in inches — convert millimeters to inches by dividing by 25.4 (a 50 mm ID = 1.969") — and returns liters alongside gallons and cubic feet.
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Common Questions About Pipe Volume
How do you calculate the volume of a pipe?
Pipe volume = π × (inner radius)² × length. Find the pipe's inner diameter, halve it to get radius, square it, multiply by π (3.14159), and multiply by pipe length in inches. Divide by 231 to convert cubic inches to US gallons, or by 1728 for cubic feet. This calculator handles the math — just enter size and length.
What is the difference between nominal pipe size and inner diameter?
Nominal pipe size is a standardized label, not the actual measurement. A nominal 2" Schedule 40 pipe has an outer diameter of 2.375" and an inner diameter of 2.067". Wall thickness varies by schedule: Schedule 80 is thicker, so the ID is smaller and volume per foot is less. Always use actual inner diameter for volume calculations.
How many gallons are in a 100-foot run of 2-inch pipe?
A 100-foot run of 2-inch Schedule 40 pipe (ID 2.067") holds approximately 17.4 gallons. Schedule 80 of the same nominal size (ID 1.939") holds about 15.3 gallons.
How do I calculate how long it takes to fill a pipe?
Divide pipe volume in gallons by flow rate in GPM. A pipe holding 17.4 gallons at a 5 GPM supply takes 3.5 minutes to fill. Use this calculator's flow rate field to get fill time automatically.
Why does pipe volume matter for plumbing contractors?
Pipe volume drives expansion tank sizing, chemical and glycol dosing, pressure test planning, and flush duration. Underestimating volume leads to undersized expansion tanks, undertreated systems, and incomplete flushes — all of which cause callbacks.
How much does pipe schedule affect volume?
Significantly for large pipe. A nominal 4" Schedule 40 pipe (ID 4.026") holds 0.660 gal/ft; Schedule 80 (ID 3.826") holds about 0.597 gal/ft — 10% less. Use the custom ID field in this calculator for non-Schedule-40 pipe.
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Related Guides & Tools
Volume calculations are based on Schedule 40 inner diameters per ASME B36.10M unless a custom inner diameter is entered. Verify specifications against actual pipe data sheets before use in system design. All calculations are estimates based on historical information and should be verified by the user. This tool is provided as a free service for planning purposes only and is not a substitute for a professional assessment, a supplier quote, or applicable local code requirements.
Frequently Asked Questions
- How do you calculate the volume of a pipe?
- Pipe volume = π × (inner radius)² × length. In practical terms: find the inner diameter (ID) of your pipe in inches, halve it to get the radius, square it, multiply by π (3.14159), and then multiply by the pipe length in inches. Divide by 231 to convert cubic inches to US gallons, or by 1728 for cubic feet. This calculator handles all of that automatically — just enter pipe size and length.
- What is the difference between nominal pipe size and inner diameter?
- Nominal pipe size (NPS) is a standardized label — a 2" pipe is not actually 2 inches in diameter. For Schedule 40 pipe, a nominal 2" pipe has an outer diameter of 2.375" and an inner diameter of 2.067". The wall thickness depends on the schedule: Schedule 40 and Schedule 80 have different wall thicknesses (Schedule 80 is thicker/smaller ID) and will hold different volumes. Always use the actual inner diameter for volume calculations.
- How many gallons of water are in a 100-foot run of 2-inch pipe?
- A 100-foot run of 2-inch Schedule 40 pipe (inner diameter 2.067") holds approximately 17.4 gallons. The formula: π × (1.0335)² × (100 × 12) = 4,013 cubic inches ÷ 231 = 17.4 gallons. Larger or smaller schedule ratings change the inner diameter and therefore the volume.
- How do you calculate how long it takes to fill a pipe?
- Divide the pipe volume (in gallons) by the flow rate (in gallons per minute). For example, a pipe holding 17.4 gallons with a 5 GPM flow rate takes 17.4 ÷ 5 = 3.5 minutes to fill. This matters for commissioning systems, pressure testing, and flushing procedures. This calculator includes an optional fill time calculation — enter your flow rate in GPM to get the fill time.
- Why does pipe volume matter for plumbing contractors?
- Pipe volume is critical for: (1) Sizing expansion tanks — undersized tanks cause pressure spikes and relief valve discharge. (2) Pressure testing — knowing volume helps calculate system pressure drop from a leak. (3) Chemical treatment — glycol, descalers, and disinfectants are dosed by system volume. (4) Flush times — you need to move at least 1–2 pipe volumes to fully flush a system. (5) Fill and drain times — critical for scheduling on job sites with shared water sources.
- How much does pipe schedule affect volume?
- Schedule affects wall thickness, which changes the inner diameter and therefore volume. For a nominal 2" pipe: Schedule 40 has an ID of 2.067" (17.4 gal/100 ft), Schedule 80 has an ID of 1.939" (15.3 gal/100 ft). That's about 12% less volume in Sch 80. For large systems with glycol or chemical treatments, this difference matters for correct dosing. Use the Custom entry in this calculator to enter your pipe's exact inner diameter if you're on a non-standard schedule.
- How many gallons per foot does a 4-inch pipe hold?
- A 4-inch Schedule 40 pipe (inner diameter 4.026") holds approximately 0.660 gallons per linear foot. A 100-foot run holds about 66 gallons. A 4-inch Schedule 80 pipe has an inner diameter of 3.826" and holds about 0.597 gallons per foot — about 10% less than Schedule 40.
- How do I calculate glycol volume for a hydronic system?
- First calculate total pipe volume using this calculator for each pipe segment, then add the volume of all terminal units, the boiler heat exchanger, and the expansion tank. Glycol manufacturers specify dose as a percentage of total system volume — typically 30% for freeze protection to about 0°F or 50% for protection to -30°F. Multiply total system volume by the glycol percentage to get the glycol volume needed.
- How much water is in a pipe?
- The amount of water in a pipe depends on its inner diameter and length. As a quick reference for Schedule 40 pipe per 100 feet: 1/2" holds about 1.6 gallons, 3/4" about 2.8 gallons, 1" about 4.5 gallons, 2" about 17.4 gallons, 4" about 66 gallons, and 6" about 150 gallons. For any other size or length, enter the inner diameter and run length in the calculator above to get the exact volume in gallons, cubic feet, and liters.
- Can I use this calculator for metric or millimeter pipe sizes?
- Yes. The calculator works from the inner diameter in inches, so for metric pipe, convert the inner diameter from millimeters to inches by dividing by 25.4 (for example, a 50 mm ID = 50 ÷ 25.4 = 1.969"), then enter that value in the 'Enter inner diameter' field. Results are shown in liters as well as US gallons and cubic feet, so you get metric output either way.