Gas Pipe Volume Calculator
Same volume in every unit
Fluid weight
Estimated fill / drain time
Your recent calculations (saved on this device)
| When | ID | Length | Result |
|---|
This gives the geometric internal volume. For gas quantity, apply a pressure correction (see 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.
Geometric volume vs gas quantity
There are two different "volumes" for a gas line, and mixing them up causes real errors. The geometric volume is the physical space inside the pipe — area of the bore times length — and it does not change with pressure. The gas quantity is how much gas that space holds, which does depend on pressure and temperature because gases compress. This calculator gives the geometric volume; the section below shows how to convert it.
Turning geometric volume into standard volume
A rough, room-temperature conversion for the gas contained is:
Standard volume ≈ Geometric volume × (absolute pressure ÷ standard pressure)
Absolute pressure = gauge pressure + atmospheric (~14.7 psi). Use consistent absolute units.
For example, 100 ft of 2-inch pipe has a geometric volume of about 2.33 ft³. At 100 psi gauge (≈114.7 psia), it contains roughly 2.33 × (114.7 ÷ 14.7) ≈ 18.2 standard cubic feet of gas. This is an ideal-gas estimate; real gases and precise work need a compressibility factor and the actual temperature.
Where gas-line volume is used
- Purging — the geometric volume is the space to sweep clear of air or product.
- Leak-down and pressure decay — line volume affects how fast pressure falls.
- Compressed-air storage — long runs add usable receiver volume.
- Nitrogen and inert-gas systems — charge and purge quantities.
Compressed-air pipe as extra storage
Shop air mains hold more than people expect. A 200 ft run of 2-inch pipe is about 4.66is about 4.5 ft³ ofnbsp;ft³ of geometric volume; charged to 100 psi, that is roughly 36 standard cubic feet of stored air — enough to smooth out short demand spikes. The geometric figure from this tool is the starting point for that kind of sizing.
Safety and accuracy notes
Gas work is regulated for good reason. This calculator is a volume tool, not a sizing or safety authority: it does not size gas pipe for load, pressure drop or code compliance, and it does not evaluate leaks. Use the geometric volume for purge and pressure-decay estimates, apply a proper compressibility correction for accurate quantities, and follow the relevant code and a qualified professional for anything involving fuel gas.
Reading and trusting your result
Here is how to read the number this gas pipe volume calculator gives you, and where it stops being exact.
What the figure represents
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.
Internal volume of a Schedule 40 gas run
Gas pipe is still steel, so the geometric (empty) volume follows the same Schedule 40 bores as water pipe. This is what a 1" Sch 40 service line (bore 1.049 in) contains as it gets longer — the figure you need before applying pressure or a purge calculation.
| Length (ft) | Volume (US gal) | Per foot |
|---|---|---|
| 10 ft | 0.45 | 0.0449 |
| 25 ft | 1.12 | 0.0449 |
| 50 ft | 2.25 | 0.0449 |
| 100 ft | 4.49 | 0.0449 |
| 250 ft | 11.23 | 0.0449 |
| 500 ft | 22.46 | 0.0449 |
Common gas-pipe sizes at a glance
Geometric volume held by a fixed 100 ft run across the Schedule 40 sizes used for gas and air, in US gal. This is line volume at atmospheric conditions, before any density or pressure correction.
| Nominal size | Bore (in) | Volume in 100 ft (US gal) |
|---|---|---|
| 1/2" | 0.622 | 1.58 |
| 3/4" | 0.824 | 2.77 |
| 1" | 1.049 | 4.49 |
| 1-1/4" | 1.380 | 7.77 |
| 2" | 2.067 | 17.43 |
Reading it for a purge
- Suppose a 3/4" Sch 40 branch (bore 0.824 in) runs 60 ft.
- Per-foot geometric volume = 0.0277 US gal, so line volume = 0.0277 × 60 = 1.66 US gal (0.222 ft³).
- A safe purge typically moves several pipe-volumes of gas; multiply this figure by your purge factor to size the sweep.
- Remember: this is geometric volume — the mass of gas inside also depends on pressure and temperature.
Frequently asked questions
How do I calculate the volume of a gas pipe?
Start with the geometric internal volume: area of the bore × length. Enter the bore and length above. For the gas quantity, multiply by absolute pressure ÷ standard pressure.
Does gas pipe volume change with pressure?
The geometric volume of the pipe does not. The amount of gas inside does, because gases compress — higher pressure means more gas in the same space.
What is standard cubic feet (SCF) for a gas line?
It is the gas quantity expressed at standard conditions. Approximate it as geometric ft³ × (absolute pressure ÷ standard pressure); precise work needs a compressibility factor and temperature.
Can I use this to size a gas pipe?
No. This tool gives volume only. Sizing gas pipe for load, pressure drop and code must follow the relevant standard and a qualified professional.
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What people say
The fill-time estimate turned a vague flush task into a scheduled one. Handy.
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Clean and quick on my phone in the field.