What this calculator does
This Pipe Volume Capacity Calculator tells you how much water (or any liquid) a length of pipe can hold based on its inside diameter and length. It treats the pipe as a perfect cylinder and reports the capacity in liters, US gallons, cubic meters, and cubic feet so you can plan plumbing, irrigation, draining, or flushing jobs.
How to use it
Enter the inside (internal) diameter and the pipe length, then choose the unit they are measured in (meters, centimeters, inches, or feet). Always use the inside bore, not the outside diameter, because pipe walls do not hold water. The calculator instantly returns the total volume in several common units.
The formula explained
The internal volume of a cylinder is the cross-sectional area times the length. The cross-section is a circle of area \(\pi D^{2}/4\), so the volume is $$V = \frac{\pi D^{2}}{4} \times L.$$ The diameter and length are converted to meters to produce cubic meters, then \(1\ \text{m}^{3} = 1000\) liters, and gallons are found by dividing liters by \(3.785411784\).
Worked example
For a pipe with a 1 m inside diameter and 2 m length: $$V = \frac{\pi \times 1^{2}}{4} \times 2 = 1.570796\ \text{m}^{3} = 1570.8\ \text{liters}.$$ Dividing by \(3.785411784\) gives about 415 US gallons.
FAQ
Should I use inside or outside diameter? Use the inside diameter — that is the space water actually occupies.
Does it handle non-full pipes? No, it assumes the pipe is completely full. Multiply by your fill fraction for partial fills.
Are these US or imperial gallons? US liquid gallons (1 gal = 3.785411784 liters). UK gallons are larger.
