Pipe Volume Calculator — Cubic Feet
Same volume in every unit
Fluid weight
Estimated fill / drain time
Your recent calculations (saved on this device)
| When | ID | Length | Result |
|---|
Result is shown in cubic feet by default; every other unit is in the cards below.
How to use this calculator
- Choose the unit system — US, Imperial or metric — at the top of the calculator.
- Pick the pipe type and schedule, then the nominal size, and the real inside diameter loads for you. Or choose Custom and type any bore.
- Enter the pipe length. Open Advanced to set fill level, number of identical runs, a fittings allowance, the fluid, or a flow rate.
- Press Calculate to see the volume in every unit, plus fluid weight, cross-section area and fill or drain time.
- Copy, share or print the result. Recent calculations are saved on your own device so you can reopen them later.
Tip: not sure where to start? Use the Fill example data button to load a complete worked example — a 2-inch Schedule 40 line, 50 ft long, at 10 gal/min — then adjust the numbers to match your job.
Real-world uses, with numbers
Charging a radiant-heat loop
How much water sits in a 300 ft run of ½" PEX.
≈ 2.9 US galSizing a well pressure tank
Line-fill volume in 100 ft of 1" Schedule 40.
≈ 4.5 US galFlushing a main
Water to displace in 100 ft of 4" Schedule 40.
≈ 66 gal · 250 LWater weight on hangers
Load from a full 100 ft run of 2" pipe.
≈ 145 lb · 66 kgMetric heating fill
Charge volume for 50 m of 28 mm bore.
≈ 30.8 LFuel or oil line contents
Diesel held in 20 m of 50 mm bore.
≈ 39 L · 33 kgMore questions, answered
How do I convert between gallons, litres and cubic metres?
1 US gallon = 3.785 litres; 1 Imperial gallon = 4.546 litres; 1 m³ = 1,000 litres = 264.2 US gallons. The calculator shows all of them from a single entry, so you never convert by hand.
Does the pipe material change the volume?
Only through the bore. Two pipes with the same inside diameter hold the same volume whether they are steel, PVC, copper or PEX. Material and schedule matter because they set the real inside diameter for a given nominal size.
How much does the water inside a pipe weigh?
About 8.34 lb per US gallon, or 1 kg per litre. A full 100 ft run of 2" Schedule 40 holds roughly 17.4 gallons, about 145 lb. Set the fluid in Advanced for hot water, glycol, diesel or seawater.
What if I only know the outside diameter?
Switch the diameter to OD mode and enter the wall thickness; the tool subtracts two wall thicknesses to reach the bore. For a listed standard, just pick the size and the published inside diameter loads automatically.
Can I use it for a part-full or sloped drain?
Yes for a straight, round pipe: open Advanced and set the fill level below 100%, and the volume scales with it. Truly partial gravity flow in a sloped line follows a curved free surface, so treat the part-full figure as an approximation.
Notes and derived figures
- Volume scales with the square of the bore: doubling the inside diameter roughly quadruples the capacity, while doubling the length only doubles it.
- Per-foot and per-metre capacity are constant for a given bore, so any length is a single multiplication — handy for quick field estimates.
- Nominal size is a label. A "2-inch" Schedule 40 pipe has a 2.067-inch bore; using "2" overstates the volume by more than a third.
- Fill and drain time is volume divided by flow rate. Enter a flow rate in Advanced to turn any result into a charge, flush or drain time.
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.