Pipe Volume Calculator

This pipe volume calculator works out how much water a pipe holds from its inside diameter and length. Volume = π × (inside diameter ÷ 2)² × length, which for US gallons is 0.0408 × ID² (in inches) per foot of pipe.

Use the calculator Plumbing invoice template

Reviewed October 2026 · by the BrickByClick team

At a glance

What it does: US gallons, litres, cubic feet, gallons per foot and water weight for any pipe run.
Pipe sizes built in: Schedule 40 steel and PVC, copper type L and M, and PEX, or type your own inside diameter.
What it costs: nothing. It runs in your browser, and nothing you type is sent or stored.

Pipe capacity calculator

Choose the pipe and size, or enter the inside diameter yourself, then the length of the run.

Preset diameters are typical published values. Real pipe varies by maker and wall thickness, so use a measured or catalogue inside diameter when the answer matters, such as dosing chemicals or sizing an expansion tank.

Pipe volume formula

A pipe is a cylinder, so its volume is the area of the inside circle times the length. Always use the inside diameter, not the nominal size: a 2 in Schedule 40 pipe is 2.067 in inside.

volume = π × (inside diameter ÷ 2)² × length
US gallons per foot = 0.0408 × (inside diameter in inches)²
litres per metre = 0.000785 × (inside diameter in mm)²

The 0.0408 comes from π ÷ 4 × 12 in ÷ 231 cubic inches per US gallon. One cubic foot holds 7.4805 US gallons, and one US gallon is 3.7854 litres.

Worked example

100 ft of 2 in Schedule 40 pipe, inside diameter 2.067 in:

Gallons per foot: 0.0408 × 2.067² = 0.0408 × 4.2725 = 0.1743.
Total: 0.1743 × 100 = 17.43 US gallons.
In litres: 17.43 × 3.7854 = 66.0 L.
Water weight: 17.43 × 8.34 lb = about 145 lb.

Those are the numbers the calculator opens with.

Pipe volume chart: gallons per foot by pipe size

Typical inside diameters and how much water each size holds.

US gallons per foot = 0.0408 × ID²
Pipe	Inside dia.	Gal per ft	Gal per 100 ft	L per m
Schedule 40 steel or PVC 1/2"	0.622 in	0.0158	1.58	0.196
Schedule 40 steel or PVC 3/4"	0.824 in	0.0277	2.77	0.344
Schedule 40 steel or PVC 1"	1.049 in	0.0449	4.49	0.558
Schedule 40 steel or PVC 1-1/4"	1.380 in	0.0777	7.77	0.965
Schedule 40 steel or PVC 1-1/2"	1.610 in	0.1058	10.58	1.313
Schedule 40 steel or PVC 2"	2.067 in	0.1743	17.43	2.165
Schedule 40 steel or PVC 2-1/2"	2.469 in	0.2487	24.87	3.089
Schedule 40 steel or PVC 3"	3.068 in	0.3840	38.40	4.769
Schedule 40 steel or PVC 4"	4.026 in	0.6613	66.13	8.213
Schedule 40 steel or PVC 6"	6.065 in	1.5008	150.08	18.639
Schedule 40 steel or PVC 8"	7.981 in	2.5988	259.88	32.275
Schedule 40 steel or PVC 10"	10.020 in	4.0963	409.63	50.874
Schedule 40 steel or PVC 12"	11.938 in	5.8146	581.46	72.214
Copper type L 1/2"	0.545 in	0.0121	1.21	0.151
Copper type L 3/4"	0.785 in	0.0251	2.51	0.312
Copper type L 1"	1.025 in	0.0429	4.29	0.532
Copper type L 1-1/4"	1.265 in	0.0653	6.53	0.811
Copper type L 1-1/2"	1.505 in	0.0924	9.24	1.148
Copper type L 2"	1.985 in	0.1608	16.08	1.997
Copper type L 3"	2.945 in	0.3539	35.39	4.395
Copper type L 4"	3.905 in	0.6222	62.22	7.727
Copper type M 1/2"	0.569 in	0.0132	1.32	0.164
Copper type M 3/4"	0.811 in	0.0268	2.68	0.333
Copper type M 1"	1.055 in	0.0454	4.54	0.564
Copper type M 1-1/4"	1.291 in	0.0680	6.80	0.845
Copper type M 1-1/2"	1.527 in	0.0951	9.51	1.182
Copper type M 2"	2.009 in	0.1647	16.47	2.045
Copper type M 3"	2.981 in	0.3626	36.26	4.503
Copper type M 4"	3.935 in	0.6318	63.18	7.846
PEX (SDR 9, approx.) 1/2"	0.475 in	0.0092	0.92	0.114
PEX (SDR 9, approx.) 3/4"	0.671 in	0.0184	1.84	0.228
PEX (SDR 9, approx.) 1"	0.862 in	0.0303	3.03	0.377

How much water is in a pipe? Common uses

Flushing and disinfecting a line: the volume tells you how much water it takes to fill the line once, and how much disinfectant to add for a target dose.
Hydronic and glycol systems: add the pipe volume to the boiler, emitter and tank volumes to size an expansion tank or order glycol.
Wait time for hot water: a long 3/4 in line holds a lot of cold water before hot arrives, which is useful when you plan a recirculation loop.
Draining and filling: know how much will come out before you open a valve.

Fittings, valves and tanks add volume the calculator does not count, so add them for system totals.

From the job site to the invoice

Price the job with the margin calculator and bill it with the plumbing invoice template. To email invoices with a card payment link, BrickByClick Free is $0 a month; Starter, $99 a month, adds estimates, jobs, a calendar and the crew app.

Sources

US gallon = 231 cubic inches; 1 inch = 2.54 cm; 1 US gallon = 3.785411784 L: NIST Handbook 44, Appendix C (General Tables of Units of Measurement).
Schedule 40 inside diameters (ASME B36.10): The Engineering ToolBox, steel pipe dimensions. PVC Schedule 40 (ASTM D1785) shares the same outside diameters and walls.
Copper type L and M inside diameters (ASTM B88): The Engineering ToolBox, copper tubes ASTM B88.
PEX SDR 9 dimensions (ASTM F876): The Engineering ToolBox, ASTM F876 PEX tube. Inside diameters vary by maker; the presets are approximate.
Water weighs about 8.34 lb per US gallon: USGS Water Science School, Water Density.

Questions people ask

How do I calculate the volume of a pipe?

Multiply π by the inside radius squared and by the length: V = π × r² × L. For US gallons per foot, use 0.0408 × the inside diameter in inches squared.

How many gallons are in 100 feet of 2 inch pipe?

About 17.4 US gallons for 2 in Schedule 40 pipe (inside diameter 2.067 in): 0.0408 × 2.067² × 100 = 17.43 gallons, or about 66 litres.

How many gallons per foot are in a 3/4 inch pipe?

About 0.028 gallons per foot for 3/4 in Schedule 40 (ID 0.824 in), 0.025 for 3/4 in copper type L (ID 0.785 in) and 0.018 for 3/4 in PEX (ID about 0.671 in).

Should I use the inside or outside diameter?

The inside diameter. The water only fills the bore. Nominal pipe sizes are names, not measurements: a 1 in Schedule 40 pipe is 1.049 in inside and 1.315 in outside.

How many gallons are in a cubic foot?

7.4805 US gallons. A US gallon is defined as 231 cubic inches, and a cubic foot is 1,728 cubic inches, so 1,728 ÷ 231 = 7.4805.

How do I convert pipe volume to litres?

Multiply US gallons by 3.7854. Or work in metric: litres per metre = 0.000785 × the inside diameter in millimetres squared.

How much does the water in a pipe weigh?

About 8.34 pounds per US gallon, or about 1 kg per litre. 100 ft of 2 in Schedule 40 pipe holds about 17.4 gallons, roughly 145 lb of water.

Does pipe schedule change the volume?

Yes. Higher schedules have thicker walls and a smaller bore at the same nominal size. A 2 in Schedule 80 pipe holds less than a 2 in Schedule 40. Use the right inside diameter for the schedule.

Does the calculator include fittings and tanks?

No. It counts straight pipe only. Add the volume of tanks, boilers, coils and large fittings for a system total.

Are the preset pipe sizes exact?

They are typical published inside diameters. Real pipe varies with the maker and tolerances, especially plastic, so enter a measured or catalogue diameter when you need a precise figure.

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