Pipe Volume Calculator
This pipe volume calculator finds how much water or other liquid a pipe holds from its inside diameter and length. Enter the bore in millimeters and the length in meters, and the pipe volume calculator returns the volume in liters, cubic meters, and US gallons, so you can size fills, flushes, and chemical doses.
Results
The Pipe Volume Calculator is part of our Fluids collection. Browse more fluids to size, convert, and check your work alongside this tool.
What the pipe volume calculator does
A pipe is a cylinder, so the volume inside a pipe is the area of the bore times the length. The pipe volume calculator takes the inside diameter, works out the round cross section, multiplies by the length, and converts the result to liters, cubic meters, and gallons. It answers the common site questions: how much water is in this line, how long it takes to fill, and how much inhibitor or disinfectant a flush needs.
Pipe volume formula
The volume of a pipe is the bore area times the length:
D is the inside diameter and L the length. One cubic meter is 1,000 liters, and one liter is 0.264172 US gallons, which is how the pipe volume calculator gallons figure is found.
Pipe volume calculator example
A 10 m run of pipe with a 50 mm bore:
A 30 m run of 100 mm pipe holds 235.619 liters, or 62.244 gallons. Doubling the diameter quadruples the volume, so the bore matters far more than the length.
How to use the pipe volume calculator
Enter the inside diameter of the pipe in millimeters and the run length in meters, then press Calculate. Use the true bore from the pipe schedule or the maker table, not the nominal size, because the wall thickness changes the bore. For a system with several sizes, run each size through the pipe volume calculator and add the results.
Reading the volume of a pipe
The liters figure is what you dose chemicals against and what you fill or drain. Divide it by the pump flow rate in liters per minute to get the fill time. The gallons figure suits US fixtures and chemical labels. For heating and cooling loops, add the pipe volume to the volume of boilers, coils, and tanks to get the system total for antifreeze and expansion vessel sizing.
When to use a pipe capacity calculator
- Sizing antifreeze or inhibitor for a heating loop
- Working out water for pressure testing and flushing
- Dosing chlorine to disinfect a new water main
- Finding fill and drain times with a known pump flow
- Estimating liquid in a tube, hose, or drain line
Common pipe volume calculator mistakes
- Using nominal size. Enter the true inside diameter.
- Mixing units. Diameter goes in millimeters and length in meters.
- Using the radius. The field takes the full diameter.
- Forgetting fittings and equipment. Boilers, coils, and tanks add volume.
Tips for accurate pipe volume figures
- Keep a liters per meter list for the pipe sizes you use most.
- Round up chemical doses slightly for fittings and bends.
- Measure long runs from the drawings, not by eye.
How to calculate pipe volume for a whole system
Real systems mix pipe sizes, so the fastest method is liters per meter. Build a short list of each size and its total length, multiply each length by the liters per meter from the chart, and add the totals. A heating system with 40 m of 22 mm copper (about 0.3 liters per meter for the bore), 25 m of 28 mm, and a few radiators may hold 60 to 100 liters once emitters and the boiler are added. Nominal sizes hide the true bore: steel schedule 40 and schedule 80 pipe of the same nominal size have different bores, and plastic pipe sized by outside diameter has a bore well below its name. Use the maker table for the bore, enter it in millimeters, and the pipe volume calculator stays accurate. For the empty pipe weight rather than its water content, switch to a pipe weight tool.
Volume inside a pipe and flow time
Volume tells you how much; flow rate tells you how fast. Divide the volume by the flow to get the time to fill, drain, or replace the contents: 235.6 liters in a 30 m, 100 mm main takes about 4 minutes to replace at 60 liters per minute. Disinfection and flushing procedures often ask for several full volume changes, so the time scales by that number. Work out the flow from the bore and velocity with the flow rate calculator, and for open tanks at the end of the line use the tank volume calculator.
Pipe volume chart
Water held per meter and per 100 ft of pipe by inside diameter:
| Inside diameter | Liters per meter | US gallons per meter | US gallons per 100 ft |
|---|---|---|---|
| 15 mm | 0.177 | 0.047 | 1.42 |
| 20 mm | 0.314 | 0.083 | 2.53 |
| 25 mm | 0.491 | 0.130 | 3.95 |
| 32 mm | 0.804 | 0.213 | 6.48 |
| 40 mm | 1.257 | 0.332 | 10.12 |
| 50 mm | 1.963 | 0.519 | 15.81 |
| 65 mm | 3.318 | 0.877 | 26.72 |
| 80 mm | 5.027 | 1.328 | 40.47 |
| 100 mm | 7.854 | 2.075 | 63.24 |
| 150 mm | 17.671 | 4.668 | 142.29 |
| 200 mm | 31.416 | 8.299 | 252.96 |
Pipe Volume Calculator FAQ
How do you calculate the volume of a pipe?
Multiply π by the inside radius squared and by the length. With the diameter in millimeters, liters per meter equals π × D² ÷ 4,000; a 50 mm pipe holds 1.963 liters per meter.
Do I use the inside or outside diameter?
Use the inside diameter. The outside diameter includes the wall, which holds no liquid, and because volume depends on the diameter squared, a small error grows fast.
How many gallons are in a pipe?
Find liters with the pipe volume calculator and multiply by 0.264172. A 100 mm pipe holds about 2.075 US gallons per meter, or 63.24 gallons per 100 ft.
Can I use it for tubes and hoses?
Yes. Any round tube works the same way; enter its bore and length. The calculator works as a tube volume calculator for hoses, tubing, and drain lines.