Fluid Mechanics

Pipe Volume Calculator

Find how much water a pipe holds from its inside diameter and length, in gallons, liters, cubic feet and cubic meters.

Formula V = π d² L / 4Reviewed Sep 19, 2026

A pipe holds a cylinder of fluid: volume equals the bore area times the length. The catch is that a pipe's nominal size is not its inside diameter. A 1 inch pipe has a bore of 1.049 in in Schedule 40, 0.957 in in Schedule 80, 1.025 in in Type L copper and 0.875 in in PEX, so a foot of 1 inch Schedule 40 holds about 44% more than a foot of 1 inch PEX. This pipe volume calculator fills in the real inside diameter for common sizes, or lets you type the inside diameter or outside diameter and wall thickness yourself. It returns gallons, liters, cubic feet, cubic meters and the weight of the water, or works backwards to the length that holds a given volume.

Calculation Bench

Solve for

Diameter Input

Pipe Type

Nominal Size

01Pipe Length

L · Total straight length of the run

Show Result In

Solution

Choose a pipe size and enter the length to get the volume it holds.

V = π d² L / 4

Formula Sheet

V=\dfrac{\pi d^{2}L}{4}

L=\dfrac{4V}{\pi d^{2}}

d=D-2t

VPipe Volume
dInside Diameter
LPipe Length
DOutside Diameter
tWall Thickness

Variables & Units

Symbol	Variable	Description	Common Units
V	Pipe Volume	Volume of liquid the full pipe holds.	US gal, L, ft³, m³
d	Inside Diameter	Bore of the pipe, the diameter of the space that holds liquid.	in, mm
L	Pipe Length	Length of straight pipe.	ft, m
D	Outside Diameter	Diameter measured across the outside of the pipe.	in, mm
t	Wall Thickness	Thickness of the pipe wall.	in, mm

How to Use This Calculator

01Choose Volume to find how much a pipe holds, or Length for Volume to find how much pipe holds a set amount of liquid.
02Pick how you know the diameter: a standard pipe size (the calculator uses the actual bore), the inside diameter directly, or the outside diameter and wall thickness.
03For a standard size, pick the pipe type (Schedule 40, Schedule 80, copper Type L or PEX) and the nominal size printed on the pipe or fitting.
04Enter the pipe length, or in Length mode the volume you want to hold.
05Read the volume in your unit, plus gallons per foot, liters per meter and the weight of the water in the full pipe.

How the Formula Works

The inside of a straight pipe is a cylinder. Its volume is the circular bore area multiplied by the length: V = π d² L / 4, where d is the inside diameter.

Only the inside diameter counts. Wall thickness takes up space without holding liquid, which is why the nominal size printed on the pipe is misleading. When you know the outside diameter D and the wall thickness t, the bore is d = D − 2t.

Volume grows with the square of the diameter. Doubling the bore gives four times the volume per foot, so a small error in the bore is squared in the result.

To find how much pipe holds a target volume, the same formula is rearranged to L = 4V / (π d²). The weight of the water uses 998.2 kg/m³ (8.33 lb per US gallon).

The result is the volume of a completely full, straight pipe. Fittings, valves, and partly filled or sloped pipes are not included.

Worked Example 01

100 ft of 2 in Schedule 40 PVC

Known

Pipe: 2 in Schedule 40 (bore 2.067 in = 0.05250 m)
Length: 100 ft (30.48 m)

Formula

V = π d² L / 4

Substitution

V = π × 0.05250² × 30.48 / 4 = 0.06599 m³

Result

17.43 US gal (65.99 L, 2.33 ft³)

The nominal size is 2 in, but the bore is 2.067 in. The run holds about 17.4 gallons, which is 0.174 gallons per foot. Full of water it weighs about 145 lb (65.9 kg), excluding the pipe itself.

Worked Example 02

50 ft of 3/4 in Type L copper

Known

Pipe: 3/4 in Type L copper (bore 0.785 in = 0.01994 m)
Length: 50 ft (15.24 m)

Formula

V = π d² L / 4

Substitution

V = π × 0.01994² × 15.24 / 4 = 0.004759 m³

Result

1.26 US gal (4.76 L)

A copper 3/4 in line holds 0.025 gallons per foot, so 50 ft holds about a gallon and a quarter. This is roughly the volume that has to run before hot water reaches a distant tap.

Worked Example 03

Length of 4 in Schedule 40 that holds 50 gallons

Known

Pipe: 4 in Schedule 40 (bore 4.026 in = 0.1023 m)
Target volume: 50 US gal (0.1893 m³)

Formula

L = 4V / (π d²)

Substitution

L = 4 × 0.1893 / (π × 0.1023²) = 23.05 m

Result

75.6 ft (23.05 m)

A 4 in Schedule 40 pipe holds 0.661 gallons per foot, so 50 gallons fills about 75 ft. Length mode is useful when the pipe is a holding volume, such as a buried storage line.

Applications

01Working out how much water a plumbing or irrigation run holds before flushing, disinfecting, or draining
02Estimating the fluid needed to fill a hydronic heating loop or chilled-water line
03Finding the weight of a water-filled pipe for hanger and support planning
04Sizing a chemical, glycol or antifreeze charge for a pipe run

US Gallons per Foot of Full Pipe by Nominal Size

Nominal size	Schedule 40	Schedule 80	Copper Type L	PEX (SDR 9)
1/2 in	0.0158	0.0122	0.0121	0.0096
3/4 in	0.0277	0.0225	0.0251	0.0189
1 in	0.0449	0.0374	0.0429	0.0312
1-1/4 in	0.0777	0.0666	0.0653	0.0466
1-1/2 in	0.1058	0.0918	0.0924	0.0651
2 in	0.1743	0.1534	0.1608	0.1115
2-1/2 in	0.2487	0.2202	0.2479	not listed
3 in	0.3840	0.3431	0.3539	not listed
4 in	0.6613	0.5972	0.6222	not listed
6 in	1.5008	1.3541	not listed	not listed
8 in	2.5988	2.3721	not listed	not listed

Nominal Size Is Not the Bore (Inside Diameter, in)

Nominal size	Schedule 40	Schedule 80	Copper Type L	PEX (SDR 9)
1/2 in	0.622	0.546	0.545	0.485
3/4 in	0.824	0.742	0.785	0.681
1 in	1.049	0.957	1.025	0.875
2 in	2.067	1.939	1.985	1.653
4 in	4.026	3.826	3.905	not listed

Assumptions

01The pipe is straight, completely full, and has a constant round bore.
02Standard-size bores: Schedule 40 and 80 follow ASTM D1785 (PVC) and ASME B36.10 (steel); copper Type L follows ASTM B88; PEX uses SDR 9 (ASTM F876), with the bore taken as outside diameter minus two minimum walls.
03Water weight uses 998.2 kg/m³ (fresh water at 20 °C). Other liquids weigh differently.
04US gallons are used (1 US gal = 3.785 L). An imperial gallon is about 20% larger.

Where This Model Stops

01Does not include the volume of fittings, valves, pumps, tanks, or heat exchangers in the system.
02Does not handle partly filled, sloped, or open-channel flow. Use the Manning Equation Calculator for those.
03Real bores vary by manufacturer and tolerance. PEX in particular varies; check the maker's data for exact values.
04Does not size pipe or find flow, velocity, or pressure loss. Use the Pipe Size Calculator and Flow Rate Calculator for that.

References

[1]
ASTM D1785 PVC plastic pipe, Schedules 40, 80 and 120
ASTM International
Source of the Schedule 40 and 80 outside diameters and wall thicknesses used for the standard-size bores.
[2]
ASTM B88 seamless copper water tube
ASTM International
Source of the Type L copper dimensions.
[3]
ASTM F876 crosslinked polyethylene (PEX) tubing
ASTM International
SDR 9 outside diameters and minimum walls used for the PEX bores.

Frequently Asked Questions

How do you calculate the volume of a pipe?

Multiply the bore area by the length: V = π × d² × L / 4, where d is the inside diameter. Use the inside diameter, not the nominal size or outside diameter. For example, a 2 in Schedule 40 pipe has a 2.067 in bore, so 1 ft holds 0.174 US gallons.

Why is the volume different from the pipe's nominal size?

Nominal size is a label. The real bore depends on the wall thickness and pipe type. A 1 in nominal pipe has a bore of 1.049 in in Schedule 40, 0.957 in in Schedule 80, 1.025 in in Type L copper and 0.875 in in PEX. This calculator fills in the real bore for standard sizes.

How many gallons are in a foot of pipe?

It depends on the bore: 0.045 gal/ft for 1 in Schedule 40, 0.174 for 2 in, 0.384 for 3 in and 0.661 for 4 in. The reference table on this page lists common sizes for Schedule 40, Schedule 80, copper Type L and PEX.

How much does the water in a pipe weigh?

Fresh water weighs 8.33 lb per US gallon (0.998 kg per liter). The calculator shows the weight of the water in the full pipe. It does not include the weight of the pipe itself.

How is this different from the Pipe Size Calculator and Flow Rate Calculator?

This calculator gives the static volume a full pipe holds. The Pipe Size Calculator picks a diameter from a flow rate and target velocity, and the Flow Rate Calculator relates volume flow, velocity and area while liquid is moving.

Does it work for partly filled or sloped pipes?

No. It gives the volume of a completely full pipe. For a partly filled pipe you need the fill level and a partial-circle area, or the Manning Equation Calculator for open-channel flow.

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