Water Volume in a Pipe Calculator
How much water is sitting in that line? Enter the bore and length and this water volume in a pipe calculator tells you the water content in gallons or litres, how much it weighs, and how long it takes to fill or drain at a given flow rate.
Same volume in every unit
Fluid weight
Estimated fill / drain time
Your recent calculations (saved on this device)
| When | ID | Length | Result |
|---|
Fluid is set to water for the weight figure. Change it in Advanced for other liquids.
For a full pipe, water volume is the internal volume
When a pipe runs full, the volume of water is simply the internal volume of the pipe — there is no separate "water" calculation. So the same formula applies: cross-sectional area of the bore times length. What people usually want on top of the raw number is the weight of that water and the time to move it, which is why both are built into the result.
The weight of water in a pipe
Water is heavy: about 8.34 lb per US gallon, or very nearly 1 kg per litre. A full 100 ft run of 4-inch pipe holds around 66holds around 65 US gallonsnbsp;US gallons — close to 550 lb of water. That load matters for hangers, brackets and roof structures, and it is why draining a large system noticeably changes what the supports carry. The calculator shows the water weight in both pounds and kilograms automatically.
Water per foot of Schedule 40 pipe
| 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 |
Part-full pipes and gravity drains
Not every pipe runs full. Gravity drains, waste lines and vented systems often carry water only part of the way up the bore. Set a fill level below 100% in the Advanced section and the water volume scales to match. Bear in mind that for detailed gravity-flow design the depth of flow depends on slope and roughness, so treat the part-full figure as a sound estimate rather than a hydraulic design result.
Everyday reasons to know water content
- Flushing and disinfection — dose and dwell times are set per gallon or litre of water.
- Freeze protection — line contents tell you how much to blow out or how much antifreeze to add.
- Leak checks — a known volume makes pressure-loss and make-up-water tests meaningful.
- Structural loads — the weight of water informs support spacing and roof loading.
From water volume to fill and drain time
Enter a flow rate — from a tap, a pump or a hydrant — and the tool divides the water volume by that rate to estimate fill or drain time. This is the practical end of the calculation: you rarely want the volume for its own sake, you want to know how long a job will take or how long a chemical needs to sit in the line.
Reading and trusting your result
A volume figure is only useful if you know what it assumes — so a quick word on reading your water volume in a pipe 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.
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 water in a pipe?
For a full pipe it is the internal volume: area of the bore × length. Enter the inside diameter and length above to get the water content in gallons or litres, plus its weight.
How much does the water in a pipe weigh?
About 8.34 lb per US gallon or 1 kg per litre. The calculator shows the total water weight in both pounds and kilograms for your pipe.
How do I find water volume in a part-full pipe?
Set the fill level below 100% in Advanced. The volume scales with the fill percentage as a good estimate; use open-channel methods for design-grade gravity flow.
How long will my pipe take to fill with water?
Divide the water volume by the flow rate. Enter a flow rate in the Advanced section and the tool estimates the fill (or drain) time for you.
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What people say
Used the litres-per-metre figures to size a glycol charge for a radiant job. Numbers matched the datasheet.
Switches between US and metric without losing the pipe. Small thing, big time-saver.
Would love more HDPE DIPS sizes, otherwise excellent.