Pipe Volume Calculator
A straight 100-foot pipe with a true 2-inch inside diameter holds about 2.1817 cubic feet, 16.32 US gallons, or 61.78 liters when full. This pipe volume calculator models the internal space as a circular cylinder. Enter actual inside diameter and centerline-equivalent straight length with their units. The result does not automatically include fittings, valves, branches, tanks, wall thickness, or unfilled air space.
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.
- •Diameter can be entered in inches, feet, millimeters, or centimeters.
- •Length can be entered in inches, feet, yards, or meters.
- •US gallons are based on 231 cubic inches per gallon, not imperial gallons.
- •Because radius is squared, a small inside-diameter error can create a larger volume error.
How to Use
- 1Find the actual inside diameter from a reliable specification or measurement, not only the nominal trade size.
- 2Enter the diameter and select inches, feet, millimeters, or centimeters.
- 3Enter the straight pipe length or a carefully developed equivalent length for the volume being estimated.
- 4Select inches, feet, yards, or meters for length.
- 5Calculate and read the same internal volume in cubic feet, US gallons, and liters.
- 6Add separately calculated component volumes when fittings, equipment, tanks, or branches matter to the total system fill.
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 inside diameter and length to feet. It divides diameter by 2 for radius, then applies V = pi x radius squared x length. A 2-inch diameter becomes 1/6 foot, with radius 1/12 foot. Multiplying pi x (1/12)^2 x 100 gives 2.1816616 cubic feet. The code multiplies cubic feet by 1728 / 231 to get US gallons and by 28.316846592 to get liters. That produces about 16.32 gallons and 61.78 liters. Outputs retain ordinary floating-point precision, so practical rounding should match input accuracy.
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.
Four-inch inside diameter over 50 feet
A 4-inch diameter has a 2-inch radius. The cylinder volume is 4.3633231 cubic feet, which converts to 32.6399 US gallons and 123.5556 liters.
Metric pipe with 50 mm inside diameter
Fifty millimeters converts to 0.164042 feet and 30 meters converts to 98.4252 feet. The resulting cylinder holds 2.0802056 cubic feet or 58.9049 liters.
Small 25 mm line over 12 meters
The smaller diameter has a large effect because radius is squared. The calculated volume is 0.2080206 cubic feet, 1.5561 US gallons, or 5.8905 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.
Fittings need separate treatment when precision matters. A simple elbow may add some internal space, while a valve body, filter housing, heat exchanger, manifold, or vessel can add much more than an equal length of straight pipe.
Partially full gravity piping does not use the full-circle cylinder volume. Its liquid area depends on fill depth and pipe slope, which this calculator does not request or solve.
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
- Using outside diameter without subtracting twice the wall thickness to find the internal diameter
- Reading the gallon result as imperial gallons even though the conversion uses US gallons
- Using full-pipe capacity for a gravity drain that normally carries air above the liquid
Embed this calculator on your site
Drop this single line where you want the calculator to appear. It is responsive, mobile-friendly, resizes automatically, and is free to use with attribution.
<script src="https://calctide.com/embed.js" data-tool="pipe-volume-calculator" async></script>Preview the embed at /embed/pipe-volume-calculator/.