Water Volume in a Pipe Calculator
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.
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.
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.