BuildMeter guide · Water & Mechanical
Pipe Volume Chart
Convert known inside diameter and pipe length into internal liquid volume, with quick reference values for several example diameters.
Direct answer
What to know first
Pipe volume is based on inside diameter, not nominal trade size: volume = π × inside radius² × length. Because wall thickness varies by material and schedule, obtain the actual inside diameter from the selected pipe specification before relying on the result.
Open Pipe Volume CalculatorInside diameter controls liquid volume
A nominal pipe label does not always equal the physical inside diameter. Wall thickness changes with material, schedule, dimension ratio and pressure class. Use the inside diameter listed for the exact product, then calculate the cylinder volume.
Volume = π × (inside diameter ÷ 2)² × pipe length. Keep diameter and length in compatible units before converting the result to gallons or litres.
| Actual inside diameter | US gallons per 100 ft | Litres per 100 ft |
|---|---|---|
| 0.50 in. | 1.02 gal | 3.86 L |
| 0.75 in. | 2.29 gal | 8.69 L |
| 1.00 in. | 4.08 gal | 15.44 L |
| 1.25 in. | 6.37 gal | 24.13 L |
| 1.50 in. | 9.18 gal | 34.75 L |
| 2.00 in. | 16.32 gal | 61.78 L |
| 3.00 in. | 36.72 gal | 139.00 L |
| 4.00 in. | 65.28 gal | 247.11 L |
The chart is geometric and uses the stated actual inside diameter. It is not a nominal-size chart for PVC, steel, copper or PEX.
Worked example
A 250 ft pipe has an actual inside diameter of 1.00 in. The chart gives about 4.08 gallons per 100 ft. Multiply 4.08 × 2.5 = 10.2 gallons, or about 38.6 litres. Fittings, tanks and equipment volume are separate.
Metric calculation example
A pipe has a 50 mm inside diameter and is 30 m long. Radius is 0.025 m. Volume = π × 0.025² × 30 = 0.0589 m³. Since 1 m³ = 1,000 L, the pipe contains approximately 58.9 L.
Why nominal size can mislead
| Pipe system | Dimension that may vary | Where to verify it |
|---|---|---|
| PVC or CPVC | Inside diameter changes with schedule or SDR/DR. | Manufacturer dimension table or submittal. |
| Steel pipe | Outside diameter may stay constant while wall schedule changes. | Applicable pipe dimension standard and product data. |
| Copper tube | Type and wall thickness change inside diameter. | Tube specification and manufacturer table. |
| PEX | Inside diameter depends on tubing standard and product. | Product technical data. |
| Flexible hose | Actual bore can differ from the trade label and deform under use. | Manufacturer specifications. |
Where pipe volume matters
- System filling, flushing and chemical dosing.
- Antifreeze or hydronic fluid estimates.
- Water-heater wait time and stored hot-water volume.
- Drain-down and winterization planning.
- Weight of a liquid-filled pipe run.
- Estimating how much water is displaced during testing.
What volume does not tell you
Internal volume does not determine flow capacity by itself. Flow also depends on pressure, elevation, length, roughness, fittings, valves and allowable velocity. A larger stored volume can still have inadequate flow if the hydraulic conditions are poor.
Common mistakes
- Entering nominal size as actual inside diameter.
- Using outside diameter.
- Mixing millimetres with metres without converting.
- Forgetting fittings, manifolds, coils or equipment volume.
- Using volume alone to size pipe for pressure or flow.
Use the calculators
Enter exact inside diameter and length in the Pipe Volume Calculator. Use the Water Flow Rate Calculator and Water Velocity Calculator for separate flow scenarios.
Sources and limitations
- NIST SI units — volume
- Charlotte Pipe plastics technical manual
- Uponor example product dimensions showing actual inside diameter
Pressure rating, temperature, fluid compatibility, expansion, support, joints and system design must be verified independently from the volume calculation.