How it works
gallons = π × (inner ⌀ ÷ 24)² × length × 7.48⌀ in inches, length in feet
- inner diameter
- the bore of the pipe, in inches
- length
- the pipe length, in feet
- ÷24
- halve the inches and convert to feet
Use the inner diameter, not the outer, since only the bore carries water. Nominal pipe sizes differ slightly from the true inner diameter.
Frequently asked questions
How much water is in a pipe?
It is π × radius² × length; a 2-inch pipe 100 ft long holds about 16.3 gallons.
Do I use inner or outer diameter?
The inner diameter, since the pipe wall does not hold water.
How many gallons per foot of 2-inch pipe?
About 0.16 gallons per foot.
Does nominal size equal inner diameter?
Not exactly; nominal pipe size is close but not identical to the true bore.