Pipe Volume Calculator
This calculator finds how much water a full pipe holds by treating the run as a cylinder. Enter the inner (bore) diameter in inches and the length in feet, and it returns the volume in cubic inches, US gallons and liters at once. It is handy for flushing new lines, dosing antifreeze, or estimating how long a line takes to drain.
How to calculate pipe volume
- Measure the inner (bore) diameter of the pipe in inches, not the outside diameter, since only the inside holds water.
- Measure the total length of the pipe run in feet.
- Type the diameter into the 'Inner diameter (in)' field.
- Type the run length into the 'Length (ft)' field.
- Read the headline gallons figure, with liters underneath and cubic inches in the result cards below.
- Click 'Copy result' to copy the one-line summary for your notes.
Examples
100 ft of half-inch pipe
Inner diameter 0.5 in, length 100 ft
235.6 cubic inches, 1.02 gallons, 3.86 liters
50 ft of one-inch pipe
Inner diameter 1 in, length 50 ft
471.2 cubic inches, 2.04 gallons, 7.72 liters
200 ft of three-quarter-inch pipe
Inner diameter 0.75 in, length 200 ft
1,060.3 cubic inches, 4.59 gallons, 17.37 liters
Frequently asked questions
How do I find the volume of water in a pipe?
Treat the pipe as a cylinder. Multiply pi by the inner radius squared by the length, all in inches, to get cubic inches, then divide by 231 to get US gallons. This tool does that for you.
Should I use the inner or outer diameter?
Use the inner (bore) diameter, since only the inside of the pipe holds water. The outer diameter includes the pipe wall and would overstate the volume, more so on thick-walled pipe.
What units does the tool use?
You enter the diameter in inches and the length in feet. Results come back in cubic inches, US gallons and liters at the same time, so you can use whichever unit suits the job.
Does it use US or imperial gallons?
US gallons. The conversion uses 231 cubic inches per US gallon. An imperial gallon is larger (about 277 cubic inches), so imperial figures would be roughly 17 percent lower.
Why does pipe volume matter?
It tells you how much water sits in a line, which you need for flushing debris, purging air, dosing antifreeze before winter, chlorinating a well line, and estimating drain or heat-up time.
How many gallons are in a 100 foot garden hose?
A common 0.625 inch inner diameter hose at 100 feet holds about 1.59 gallons. Enter your hose bore and length for the exact figure, since hose diameters vary by grade.
Does it account for fittings, valves or wall thickness?
No. It assumes a plain, straight, completely full run of one constant bore. Elbows, tees, valves and pipe wall are ignored. For a system of mixed sizes, add up each straight section separately.
How accurate is the result?
The geometry is exact for a full cylindrical pipe, so accuracy depends on your inner diameter measurement. Nominal pipe sizes rarely match the true bore, so use the actual inside diameter for the closest figure.
Is my data private?
Yes. The calculation runs entirely in your browser using JavaScript. Nothing you type is uploaded to a server, so your measurements never leave your device.
Learn more
- How pipe water volume is used on real jobs
Why the water held in a pipe run matters for flushing, winterizing and chlorination, and how to measure the bore for an honest figure.
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