Pipe Volume Calculator — Cubic Feet
Cubic feet is the natural unit for air, gas and larger duct-like lines. This pipe volume calculator in cubic feet converts a bore and length straight into ft³, with cubic-feet-per-foot and conversions to gallons and cubic metres alongside.
Same volume in every unit
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| When | ID | Length | Result |
|---|
Result is shown in cubic feet by default; every other unit is in the cards below.
When cubic feet is the right unit
Liquids are usually counted in gallons or litres, but cubic feet comes into its own for gases and air volumes, for large-diameter lines, and whenever a spec sheet or duct calculation is already in imperial volume. Because a cubic foot is a fairly large unit, small pipes give small decimals — which is exactly why the calculator also reports cubic inches for tight bores.
Cubic feet from the pipe dimensions
The cleanest route keeps everything in feet:
ft³ = π × (IDft / 2)² × Lft
Convert the bore from inches to feet (divide by 12) before you start.
For example, 200 ft of 6-inch Schedule 40 pipe (bore 6.065 in = 0.5054 ft) has an area of 0.2006 ft² and a volume of about 40.1 cubic feet — roughly 300 US gallons, which the tool shows in the same result.
Converting cubic feet to other units
- 1 cubic foot = 7.4805 US gallons = 6.229 Imperial gallons.
- 1 cubic foot = 28.317 litres = 0.02832 cubic metres.
- 1 cubic foot = 1,728 cubic inches.
The result panel applies all of these automatically, so a cubic-feet answer comes with its gallon and metric equivalents attached.
Air, gas and duct volumes
For compressed-air receivers, natural-gas line contents and ventilation runs, the internal cubic feet is the geometric volume the calculator returns. Remember that gas volume changes with pressure and temperature — the geometric figure is the physical space inside the pipe, not the standard-condition gas quantity, which needs a further pressure correction.
Typical cubic-feet jobs
Sizing an air receiver or purge volume, estimating the free air a long pipe run holds, checking duct and large-bore line capacity, and reconciling a volume that a datasheet already quotes in ft³ are the everyday reasons people land here. Whatever the job, enter the bore and length once and read ft³ up top.
Reading and trusting your result
The result above answers most questions; this note covers how to interpret it and its limits.
What the number actually means
The headline value is the internal capacity of a round, uniform pipe running full — the fluid the bore can hold along the length you entered. Every other unit on the panel is the same physical quantity re-expressed, so you can quote whichever your paperwork needs without recalculating.
The full-pipe assumption
By default the figure assumes the pipe is completely full and perfectly cylindrical. For gravity drains and vented lines that run part full, set a fill level below 100% and the result scales with it. Bends, valves and fittings add a little capacity the straight-length model does not see — use the fittings allowance to approximate them.
Capacity reference tables & a worked example
Concrete numbers for this page, calculated the same way the tool above does — use them as a quick check or a lookup.
Schedule 40 2" pipe: volume by run length
How much a 2" Schedule 40 bore holds as the run gets longer, in ft³. The per-foot figure is constant, so any length is one multiplication away.
| Length (ft) | Volume (ft³) | Per foot |
|---|---|---|
| 10 ft | 0.2330 | 0.0233 |
| 25 ft | 0.5826 | 0.0233 |
| 50 ft | 1.17 | 0.0233 |
| 100 ft | 2.33 | 0.0233 |
| 250 ft | 5.83 | 0.0233 |
| 500 ft | 11.65 | 0.0233 |
Schedule 40 pipe: volume across sizes
Volume held by a fixed 100 ft run across common Schedule 40 sizes, in ft³. Doubling the diameter roughly quadruples the capacity.
| Nominal size | Bore (in) | Volume in 100 ft (ft³) |
|---|---|---|
| 1/2" | 0.622 | 0.2110 |
| 3/4" | 0.824 | 0.3703 |
| 1" | 1.049 | 0.6002 |
| 1-1/2" | 1.610 | 1.41 |
| 2" | 2.067 | 2.33 |
| 3" | 3.068 | 5.13 |
| 4" | 4.026 | 8.84 |
| 6" | 6.065 | 20.06 |
Worked example, step by step
- Bore = 2.067 in, so radius = 1.0335 in.
- Area = π × radius² = 3.3556 in².
- Length = 75 ft = 900 in; volume = 3.3556 × 900 = 3,020.0 in³.
- Convert to the unit you need: 1.75 ft³ for a 75 ft run of Schedule 40 2" pipe.
Frequently asked questions
How do I calculate pipe volume in cubic feet?
Convert the inside diameter to feet, compute π × (radius)² for the area in ft², and multiply by the length in feet. The calculator above does this and shows the conversions to gallons and m³.
How many cubic feet in a gallon?
One US gallon is 0.13368 cubic feet; equivalently, one cubic foot is 7.4805 US gallons.
Why is my small pipe showing a tiny cubic-feet number?
A cubic foot is large relative to a small bore, so thin pipes read as small decimals. Use the cubic inches card, or switch the result unit to gallons or litres for a more readable figure.
Does cubic feet work for gas volume in a pipe?
It gives the geometric internal volume in ft³. Actual gas quantity at standard conditions also depends on pressure and temperature, which is a separate correction.
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What people say
I needed line volume in ft³ for a purge sheet and got it in one shot, no unit gymnastics.
The cubic-feet figure plus per-foot saved me rebuilding a spreadsheet. Bookmarked.
Accurate and quick. An export-to-CSV button would make it perfect.