Calculator
Plumbing Pipe Volume Calculator
Work out how much water a pipe run holds, in gallons, litres, cubic feet, and pounds, from the material and nominal size, or from a bore you measured yourself. Add a run for every size change to get a system total, then check fill time, chlorination flush volume, and flush velocity. Free, no signup.
Free
Pipe runsAdd one row per size or material change. Inside diameters come from the ASTM B88, ASTM F876 and ASME B36.10M charts, pick Custom to type a measured bore.
| Material | Size | Length | Volume | Remove |
|---|---|---|---|---|
| 2.51 gal |
Bore, not nominal size, sets the volume, 1" PEX holds about a quarter less water per foot than 1" copper.
Pipe volume
2.51 gal
9.5 L · 0.34 ft³ · 21 lb of water
3.3 ft/s, meets the scour flush minimum100 ft total
Volume at a glance
Total volume
2.51 gal9.5 L · 0.34 ft³
Water weight
21 lb9.5 kg · 8.3454 lb per gallon
Volume per foot
0.0251 gal/ftgal/ft = 0.0408 × inside diameter²
Time to fill
30 secAt 5.0 GPM
Flush volume (3 pipe volumes)
7.54 gal1 min 31 sec at 5.0 GPM · scour flush
Velocity at this flow
3.3 ft/sIn the 3/4" Copper Type L run · needs 4.5 GPM to reach 3.0 ft/s
Industry benchmarks
- Scour flush velocity2.5-3.0 ft/s minAWWA C651 disinfection practice, flush until discolouration clears and the chlorine residual is restored. Confirm the figure your water authority specifies.
- Flush volume3 pipe volumesCommon utility minimum displacement before bacteriological sampling (EPA guidance says two).
- Water weight8.35 lb/galThe standard water conversion, use it to check hanger and joist loading on a filled line.
- Gallon definition231 in³US liquid gallon, exact. 1 ft³ = 7.48 gal.
- Copper Type LASTM B88 Type L, the default for domestic water and hydronic mains.
What you'll get
Add each pipe run
Pick the material and nominal size and enter the length. Inside diameters come from ASTM B88 (copper Type K, L, M), ASTM F876 (PEX), and ASME B36.10M (Schedule 40 and 80), or choose Custom and type a measured bore for hose, cast iron, or anything off-chart.
Get the volume and the weight
See total gallons, litres, cubic feet, and the weight of the water in pounds and kilograms, plus gallons per foot. Every run is totalled into one system figure and broken out row by row.
Check fill, flush, and velocity
Enter the flow rate you will actually push through the line to get time to fill, the three-pipe-volume flush required for disinfection, and whether that flow reaches the 3 ft/s scour velocity, with the GPM you would need if it does not.
How it works
- 1
Add each pipe run
Pick the material and nominal size and enter the length. Inside diameters come from ASTM B88 (copper Type K, L, M), ASTM F876 (PEX), and ASME B36.10M (Schedule 40 and 80), or choose Custom and type a measured bore for hose, cast iron, or anything off-chart.
- 2
Get the volume and the weight
See total gallons, litres, cubic feet, and the weight of the water in pounds and kilograms, plus gallons per foot. Every run is totalled into one system figure and broken out row by row.
- 3
Check fill, flush, and velocity
Enter the flow rate you will actually push through the line to get time to fill, the three-pipe-volume flush required for disinfection, and whether that flow reaches the 3 ft/s scour velocity, with the GPM you would need if it does not.
Why pipe volume decides your chlorine dose, glycol charge, and flush time
Pipe volume is the number behind three jobs that go wrong when it is guessed. Disinfecting a new water line means dosing a known volume to a target chlorine concentration, guess the volume and the residual comes back wrong and the line fails its bacteriological sample. Charging a hydronic or radiant loop means buying a known number of gallons of glycol at the right dilution. And flushing means moving a known number of pipe volumes before the water is clear. All three start with gallons, and gallons come from the bore, not the size stamped on the pipe.
That distinction is where most quick estimates go wrong. A "1-inch" pipe is not a 1-inch bore: Schedule 40 is 1.049", copper Type L is 1.025", and 1" PEX is only 0.875", which holds about 30% less water per foot than the Schedule 40. Because volume goes with the square of the diameter, a small error in the bore is a large error in the gallons. This calculator uses the published inside diameter for the material and schedule you pick, sums multiple runs into one system total, and reports gallons per foot so you can sanity-check the result against the charts on the truck.
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Pipe Volume Calculator FAQs
Treat the pipe as a cylinder: volume = π × (inside diameter ÷ 2)² × length. Working in inches and feet, the shortcut plumbers use is gallons per foot = 0.0408 × inside diameter², or equivalently inside diameter² ÷ 24.51. So 100 ft of 3/4" Schedule 40 (0.824" bore) holds 0.0408 × 0.679 × 100 = 2.77 gallons. Use the inside diameter, never the nominal size or the outside diameter.
It depends on the material, because the bore does. 3/4" Schedule 40 (0.824" ID) holds 0.0277 gal/ft, 3/4" copper Type L (0.785") holds 0.0251 gal/ft, copper Type K (0.745") holds 0.0226 gal/ft, and 3/4" PEX (0.681") only 0.0189 gal/ft. Over a 200 ft run that is the difference between 5.5 and 3.8 gallons.
Disinfection practice is to flush a minimum of three pipe volumes, at a velocity high enough to scour the pipe wall, 3 ft/s in current AWWA C651 guidance, with older editions and many utility specs citing 2.5 ft/s. This calculator gives you both: the three-volume flush quantity in gallons, and the flow rate in GPM you need to hit that velocity in the largest pipe in the system. Always confirm the requirement with your local water authority.
Time equals volume divided by flow rate: gallons ÷ GPM = minutes. A 100 ft run of 3/4" copper Type L holds 2.51 gallons, so at 5 GPM it fills in about 30 seconds. The same calculation at three pipe volumes gives your flush duration, exactly three times the fill time at the same flow.
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