How to use the pipe volume calculator
The calculator sits at the top of the page so you can get an answer before you read anything else. Three inputs are all it needs:
- Pick the pipe type (or leave it on Custom). Choosing Schedule 40, Type L copper, PEX and so on loads the true inside diameter for the size you select, so you never have to look up a bore chart by hand.
- Enter the length of the straight run in feet, metres or any unit you like.
- Read the result. The headline shows the unit you asked for; the cards below show every other unit, the per-foot and per-metre capacity, the cross-sectional area and the weight of water inside.
Everything recalculates as you type. Switching between US, Imperial and metric keeps the same physical pipe — only the units on screen change.
The formula behind pipe volume
A pipe is a cylinder, so its internal volume is the cross-sectional area of the bore multiplied by the length:
V = π × (ID / 2)² × L
ID is the internal diameter and L is the length. Both diameter terms must be in the same unit before you multiply by length.
The single most common mistake is using the nominal size or the outside diameter instead of the bore. A "2-inch" Schedule 40 pipe has a 2.375 in outside diameter and only a 2.067 in inside diameter — feeding "2" into the formula overstates the volume by more than a third. That is why this tool asks for the inside diameter and shows you which value it used.
Every unit, one calculation
Different trades want different units. A plumber sizing a water heater loop thinks in US gallons; a European heating engineer thinks in litres; an oil-and-gas planner thinks in barrels; a civil engineer pouring around a culvert thinks in cubic yards. Rather than run the numbers several times, the result panel converts a single calculation into all of them, so you can copy whichever one your paperwork needs.
Volume per foot of common Schedule 40 pipe
For quick estimates, here is how much water each foot of Schedule 40 pipe holds. Multiply by your run length, or just use the calculator above for exact figures at any length and fill level.
| Nominal size | Inside diameter | US gal / ft | US gal / 100 ft |
|---|---|---|---|
| 1/2" | 0.622" | 0.016 | 1.58 |
| 3/4" | 0.824" | 0.028 | 2.77 |
| 1" | 1.049" | 0.045 | 4.49 |
| 1-1/4" | 1.380" | 0.078 | 7.77 |
| 1-1/2" | 1.610" | 0.106 | 10.58 |
| 2" | 2.067" | 0.174 | 17.43 |
| 2-1/2" | 2.469" | 0.249 | 24.87 |
| 3" | 3.068" | 0.384 | 38.40 |
| 4" | 4.026" | 0.661 | 66.13 |
| 5" | 5.047" | 1.039 | 103.93 |
| 6" | 6.065" | 1.501 | 150.08 |
| 8" | 7.981" | 2.599 | 259.88 |
| 10" | 10.020" | 4.096 | 409.63 |
| 12" | 11.938" | 5.815 | 581.46 |
| 24" | 22.624" | 20.883 | 2088.32 |
What people calculate after the volume
Knowing the raw volume is usually step one. The extra outputs are built in because you will almost certainly want them next:
- Water weight — a full 100 ft run of 2-inch pipe holds roughly 17 US gallons, about 140 lb of water. That matters for hanging brackets and roof loads.
- Fill and drain time — enter a flow rate and the tool estimates how long the line takes to charge or empty, useful for flushing, chlorination dwell time and commissioning.
- Chemical dosing — accurate internal volume is the basis for shock-chlorination, glycol charge and pickling calculations.
- System inventory and weight — total the volume across several runs to size an expansion tank or estimate the water a system will lose if it drains.
Where this calculator is used
The same underlying calculation serves very different jobs. Homeowners use it to work out how much water sits in a garden or radiant-heat loop. Plumbers and HVAC technicians use it on site to confirm capacity before charging a system. Irrigation and pool operators use it to plan top-ups and back-flush cycles. Facility engineers log system inventory and weight for commissioning records. On the industrial side, the same tool handles fire-sprinkler flushing volumes and chemical-transfer line contents.
How accurate is it, and where are the limits
For a round, uniform, essentially full straight pipe, the result is exact to the precision of the inside diameter you enter. The realistic limits are worth knowing: bends, valves and fittings add a little volume the straight-length model does not see (use the fittings allowance to approximate it); corrugated, oval or partially full gravity lines need different geometry; and if you only have the outside diameter you must supply the wall thickness so the tool can derive the bore. Treat the figure as a solid engineering estimate for planning, and confirm against manufacturer data for anything safety-critical.
Where the pipe dimensions come from
The built-in bore values are the published standards the trades actually use: ASME B36.10 for steel and PVC schedules, ASTM B88 for copper tube types K/L/M, and ASTM F876 for PEX. HDPE is derived from its IPS outside diameter and the dimension ratio (DR) you choose. Nominal sizes are labels, not measurements — the tool always converts them to the real bore before calculating.
Reading and trusting your result
Here is how to read the number this 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.
Where the unit conversions come from
Conversions use exact factors: 231 cubic inches per US gallon, 3.785411784 litres per US gallon, 1,000 litres per cubic metre and 42 US gallons per oil barrel. Because they are exact, the only source of error is the inside diameter you supply — get the bore right and every unit is right.
Data sources and precision
Built-in bores follow ASME B36.10 (steel and PVC schedules), ASTM B88 (copper types K/L/M) and ASTM F876 (PEX); HDPE is derived from its IPS outside diameter and dimension ratio. These are nominal standard values — real pipe carries tolerances, and scale or lining reduces the effective bore in service, so treat the output as a sound engineering estimate and confirm safety-critical figures against manufacturer data.
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 US gal. The per-foot figure is constant, so any length is one multiplication away.
| Length (ft) | Volume (US gal) | Per foot |
|---|---|---|
| 10 ft | 1.74 | 0.1743 |
| 25 ft | 4.36 | 0.1743 |
| 50 ft | 8.72 | 0.1743 |
| 100 ft | 17.43 | 0.1743 |
| 250 ft | 43.58 | 0.1743 |
| 500 ft | 87.16 | 0.1743 |
Schedule 40 pipe: volume across sizes
Volume held by a fixed 100 ft run across common Schedule 40 sizes, in US gal. Doubling the diameter roughly quadruples the capacity.
| 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 |
| 1-1/2" | 1.610 | 10.58 |
| 2" | 2.067 | 17.43 |
| 3" | 3.068 | 38.40 |
| 4" | 4.026 | 66.13 |
| 6" | 6.065 | 150.1 |
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: 13.07 US gal for a 75 ft run of Schedule 40 2" pipe.
Frequently asked questions
How do I calculate the volume of a pipe?
Measure the inside diameter (ID) and the length, then apply V = π × (ID/2)² × L. Keep the diameter and length in the same unit, or let the calculator above handle the conversion. Always use the bore, not the nominal size or outside diameter.
Should I use inside or outside diameter?
Always the inside diameter for the fluid a pipe holds. The outside diameter includes the wall, which does not carry water. If you only have the OD, enter it in OD mode with the wall thickness and the tool derives the bore.
Why is nominal pipe size different from the actual diameter?
Nominal Pipe Size (NPS) is a naming convention. For sizes up to 12 inch, neither the outside nor inside diameter equals the nominal number — a 1-inch Schedule 40 pipe has a 1.315 in OD and a 1.049 in bore. Choosing a standard in the calculator loads the correct bore automatically.
Can it give the result in gallons and litres at the same time?
Yes. One calculation produces US gallons, Imperial gallons, litres, millilitres, cubic feet, cubic inches, cubic metres, barrels and cubic yards together, plus the capacity per foot and per metre.
Does it work on my phone?
Yes. The layout is mobile-first, the inputs are large enough to tap, and results update live. Your recent calculations are saved on your own device so you can reopen them later.
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What people say
I stopped second-guessing my line-fill numbers. Enter the bore, read every unit at once — done.
The per-foot readout is the one I keep coming back to on site. Fast and it uses the real bore.
Great for round pipe. Add oval duct one day and it'd cover everything I touch.