Pipe Volume Calculator
A 2-inch pipe that runs 100 feet holds about 16.32 US gallons, or 61.78 liters. This pipe volume calculator uses inside diameter and pipe length to find the internal volume in cubic feet, gallons, and liters. Use it for plumbing runs, irrigation mains, hydronic loops, and any round pipe you expect to fill completely.
Quick answer
Volume is based on the pipe's inside diameter, not its outside diameter or trade size.
What this tells you
- •Volume is based on the pipe's inside diameter, not its outside diameter or trade size.
- •The calculator treats the pipe as a full round cylinder from end to end.
- •Results include cubic feet, US gallons, and liters for the same run.
How to Use
- 1Enter the pipe's inside diameter.
- 2Choose the diameter unit, such as inches or millimeters.
- 3Enter the pipe length.
- 4Choose the length unit, then calculate to see cubic feet, US gallons, and liters.
How It Works
Formula
Volume = pi x (Inside Diameter / 2)^2 x Length
Gallons = Cubic Feet x 1728 / 231
Liters = Cubic Feet x 28.316846592The calculator converts your inside diameter and pipe length to feet, finds the cylinder volume with V = pi x r^2 x L, then converts cubic feet to US gallons and liters. Inside diameter matters because wall thickness changes the space available for water or other liquid inside the pipe.
Calculation note: values are processed in the order shown above, using the current input units.
Worked Examples
Irrigation main
A 2-inch inside diameter means a 1-inch radius. Volume = pi x (1/12 ft)^2 x 100 ft = 2.1817 cubic feet, which converts to 16.32 US gallons or 61.78 liters.
Plumbing stack or drain run
A 3-inch pipe has a 1.5-inch radius. Multiply the circular area by 40 feet of length to get 1.9635 cubic feet, then convert that volume to gallons and liters.
Sample Pipe Capacities
Common full-pipe volumes using US gallons.
| Inside Diameter | Length | Cubic Feet | US Gallons | Liters |
|---|---|---|---|---|
| 1 in | 100 ft | 0.5454 | 4.08 | 15.44 |
| 2 in | 100 ft | 2.1817 | 16.32 | 61.78 |
| 4 in | 50 ft | 4.3633 | 32.64 | 123.56 |
| 50 mm | 30 m | 2.0802 | 15.56 | 58.90 |
These values assume a straight round pipe that is completely full.
Inside Diameter Matters
Nominal pipe size does not always match the true space inside the pipe. A 2-inch Schedule 40 pipe, a 2-inch Schedule 80 pipe, and a 2-inch flexible hose can each have a different inside diameter, so the stored volume changes even when the trade size on the label looks the same.
If you are estimating water for a fill, purge, chemical dose, or freeze protection job, pull the inside diameter from the product spec sheet or pipe chart first. That small check can move the result by several percent on long runs.
Common mistakes
- Using nominal pipe size instead of the actual inside diameter
- Entering the outside diameter from a tape measure around the pipe wall
- Mixing feet and meters without checking the selected units
- Assuming fittings, valves, and manifolds are included in the straight-pipe result