Tube Volume Calculator
Same volume in every unit
Fluid weight
Estimated fill / drain time
Your recent calculations (saved on this device)
| When | ID | Length | Result |
|---|
Tube is sized by outside diameter and wall. Use OD mode with the wall thickness, or enter the bore.
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.
Tube vs pipe — the sizing difference
The words are often used loosely, but there is a real distinction. Pipe is specified by a nominal size and schedule; tube is specified by its actual outside diameter and a wall thickness (or gauge). So a "1/2-inch tube" really is 0.5 in on the outside, and its bore is 0.5 in minus twice the wall. To get tube capacity, either enter the bore directly or use OD mode and supply the wall thickness so the tool derives the bore.
Capacity from OD and wall
ID = OD − 2 × wall → V = π × (ID/2)² × L
For example, 3 m of 12 mm OD tube with a 1 mm wall has a 10 mm bore, an area of 78.5 mm², and a volume of about 0.236 litres — a little under a cup. Small-bore tubing is where millilitres and cubic inches earn their place in the result panel.
Where tubing capacity matters
- Fluid power and instrumentation — line volume affects response and bleed time.
- Lab and process tubing — internal volume for dead volume and flushing.
- Fuel, oil and brake lines — small but important line contents.
- Aquarium and hobby setups — tubing volume for dosing and turnover.
A note on gauge and drawn tube
Some tube is specified by gauge rather than a decimal wall — the lower the gauge number, the thicker the wall. If you only have a gauge, look up its decimal thickness for your tube standard and enter that as the wall. For drawn or seamless tube with tight tolerances, a direct bore measurement is the most reliable input, and Custom mode accepts it straight away.
Getting tube capacity right
The two things that move the answer are the wall thickness and whether you used OD or ID. Double-check which diameter you have, and remember that for thin-wall tube the bore is close to the OD, while for heavy-wall tube the difference is large. Once the bore is correct, the capacity is exact for a round, uniform tube.
Reading and trusting your result
A volume figure is only useful if you know what it assumes — so a quick word on reading your tube volume calculator result.
How to interpret the result
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.
3/4" OD tubing: contents by length
Tubing is called out by outside diameter and wall, so the bore takes one subtraction first. This tracks a 3/4" OD tube with a 0.049" wall (bore 0.652 in) as the run lengthens.
| Length (ft) | Volume (US gal) | Per foot |
|---|---|---|
| 10 ft | 0.17 | 0.0173 |
| 25 ft | 0.43 | 0.0173 |
| 50 ft | 0.87 | 0.0173 |
| 100 ft | 1.73 | 0.0173 |
| 250 ft | 4.33 | 0.0173 |
| 500 ft | 8.66 | 0.0173 |
Wall thickness moves the bore
Two tubes with the same outside diameter hold different amounts once the wall changes. Volume in a fixed 100 ft run for common OD/wall pairs, in US gal:
| OD × wall | Bore (in) | Volume in 100 ft (US gal) |
|---|---|---|
| 1/4" × 0.035" | 0.180 | 0.13 |
| 3/8" × 0.035" | 0.305 | 0.38 |
| 1/2" × 0.049" | 0.402 | 0.66 |
| 3/4" × 0.049" | 0.652 | 1.73 |
| 1" × 0.065" | 0.870 | 3.09 |
Working it through
- Start from a 1/2" OD tube with a 0.049" wall.
- Bore = 0.500 − 2 × 0.049 = 0.402 in, radius 0.201 in.
- Area = π × 0.201² = 0.1269 in²; across 200 ft (2,400 in) = 304.6 in³.
- That equals 1.32 US gal — and it would be larger for a thinner wall at the same OD.
Frequently asked questions
How do I calculate tube volume?
Find the bore (OD minus twice the wall), then apply V = π × (ID/2)² × L. Enter OD and wall in OD mode above, or type the bore directly.
What is the difference between tube and pipe volume?
The calculation is identical; only the sizing differs. Tube is measured by actual OD and wall, while pipe uses nominal size and schedule. Both need the true bore.
How do I find the bore from OD and gauge?
Convert the gauge to a decimal wall thickness for your tube standard, then bore = OD − 2 × wall. Enter OD and that wall in OD mode.
Can I get the result in millilitres?
Yes. The result panel includes millilitres and cubic inches, which suit small-bore tubing.
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What people say
The fill-time estimate turned a vague flush task into a scheduled one. Handy.
Clear about its own limits — tells you when to check manufacturer data. Trustworthy.
Clean and quick on my phone in the field.