Pipe volume calculator
This pipe volume calculator gives the water a pipe holds from its inside diameter and its length. The volume of a pipe is V = π × r² × L, the area of the bore times the length. In US units, gallons per foot of pipe = d² × 0.0408, with the inside diameter d in inches; in metric, liters per meter = d² × π ÷ 4 ÷ 1,000, with d in millimeters.
Contents
V = π × r² × L. A pipe with a 2 in inside diameter, 100 ft long: π × 1² × 1,200 = 3,769.9 in³ = 16.32 US gal (61.8 L). That is 0.1632 gal per foot.
The calculator above takes the inside diameter and the length, each in its own unit. It returns the volume of the line, in gallons or liters, and the volume per foot and per meter of pipe.
Volume of a pipe: the formula
A pipe is a hollow cylinder. The water fills the bore, which is a cylinder whose diameter is the inside diameter of the pipe. Its volume follows the cylinder volume formula:
V = π × r² × L = π × d² × L ÷ 4
where d is the inside diameter, r = d ÷ 2 is the inside radius and L is the length. All three must be in the same unit. A diameter in inches and a length in feet must be converted first: multiply feet by 12 to get inches.
Why gallons per foot = d² × 0.0408
Take one foot of pipe (12 in) with a bore of d inches. Its volume is π × d² × 12 ÷ 4 cubic inches. One US gallon is exactly 231 in³, so the gallons per foot are π ÷ 4 × 12 ÷ 231 × d² = 0.040800 × d². The factor rounds to 0.0408 with an error of less than 0.001 %, so it is safe for any practical use.
Liters per meter = d² × 0.000785
In metric, one meter is 1,000 mm and one liter is 1,000,000 mm³. The volume of one meter of bore is π × d² ÷ 4 × 1,000 mm³, so liters per meter = π × d² ÷ 4 ÷ 1,000 = 0.0007854 × d², with d in millimeters. A 40 mm bore holds 1,600 × 0.0007854 = 1.257 L per meter.
Gallons of water per foot of pipe: chart
The chart below is computed from the inside diameter. Use the real bore of your pipe, not its nominal size.
| Inside diameter | US gal per foot | US gal per 100 ft | Liters per meter |
|---|---|---|---|
| 1/2 in | 0.0102 | 1.02 | 0.127 |
| 3/4 in | 0.0229 | 2.29 | 0.285 |
| 1 in | 0.0408 | 4.08 | 0.507 |
| 1 1/4 in | 0.0637 | 6.37 | 0.792 |
| 1 1/2 in | 0.0918 | 9.18 | 1.140 |
| 2 in | 0.1632 | 16.32 | 2.027 |
| 2 1/2 in | 0.2550 | 25.50 | 3.167 |
| 3 in | 0.3672 | 36.72 | 4.560 |
| 4 in | 0.6528 | 65.28 | 8.107 |
| 5 in | 1.0200 | 102.00 | 12.668 |
| 6 in | 1.4688 | 146.88 | 18.241 |
| 8 in | 2.6112 | 261.12 | 32.429 |
| 10 in | 4.0800 | 408.00 | 50.671 |
| 12 in | 5.8752 | 587.52 | 72.966 |
| 14 in | 7.9968 | 799.68 | 99.315 |
| 16 in | 10.4448 | 1,044.48 | 129.717 |
| 18 in | 13.2192 | 1,321.92 | 164.173 |
| 20 in | 16.3200 | 1,632.00 | 202.683 |
| 24 in | 23.5007 | 2,350.07 | 291.864 |
Doubling the bore multiplies the volume by four, because the diameter is squared: 1 in holds 0.0408 gal per foot, 2 in holds 0.1632, 4 in holds 0.6528.
Metric bores: liters per meter
| Inside diameter | L per meter | Inside diameter | L per meter |
|---|---|---|---|
| 10 mm | 0.0785 | 65 mm | 3.318 |
| 15 mm | 0.1767 | 80 mm | 5.027 |
| 20 mm | 0.3142 | 100 mm | 7.854 |
| 25 mm | 0.4909 | 150 mm | 17.671 |
| 32 mm | 0.8042 | 200 mm | 31.416 |
| 40 mm | 1.2566 | 250 mm | 49.087 |
| 50 mm | 1.9635 | 300 mm | 70.686 |
Inside diameter, not nominal size
Pipes are sold by a nominal size, a trade name that is often close to neither the inside nor the outside diameter. Two pipes with the same nominal size can have different bores, depending on the material, the standard they follow and the wall thickness (schedule, pressure class or type). Because the bore is squared, a small difference matters: 100 ft of pipe with a 1 in bore holds 4.08 gallons, while a 0.8 in bore holds 2.61 gallons.
For an accurate volume, measure the bore with calipers at a cut end, or take the inside diameter from the manufacturer's data for your exact pipe. If you only know the outside diameter and the wall thickness, the inside diameter is OD − 2 × wall. The hollow cylinder volume page computes the bore and the wall material separately, and the cylinder weight calculator gives the weight of the pipe itself.
Worked examples
A 2 in line, 100 ft long
- Inside radius: 2 ÷ 2 = 1 in. Length: 100 × 12 = 1,200 in.
- V = π × 1² × 1,200 = 3,769.9 in³.
- 3,769.9 ÷ 231 = 16.32 US gallons, or 61.8 liters.
With the shortcut: 2² × 0.0408 × 100 = 16.32 gallons. Water weighs about 8.3 lb per gallon, so the line holds roughly 136 lb of water.
A 3/4 in supply line, 60 ft long
0.75² × 0.0408 × 60 = 1.38 US gallons (5.21 L). That is the water you run off before hot water reaches a faucet 60 ft from the heater, if the whole run has a 3/4 in bore.
A 40 mm pipe, 50 m long
r = 20 mm = 0.02 m. V = π × 0.02² × 50 = 0.06283 m³ = 62.83 liters. With the per-meter figure: 1.2566 × 50 = 62.83 L.
A 6 in pipeline, one mile long
One mile is 5,280 ft. 6² × 0.040800 × 5,280 = 7,755 US gallons. For long pipelines, carry the full factor (π ÷ 4 × 12 ÷ 231) rather than 0.0408 if you need the last gallon.
A run with several sizes
Compute each size separately and add. 40 ft of 1 in (1.63 gal) plus 25 ft of 3/4 in (0.57 gal) plus 10 ft of 1/2 in (0.10 gal) makes about 2.31 gallons. Fittings, valves and equipment such as filters or heaters add their own volume, which the pipe formula does not include.
Partly full pipes and tanks
A drain or a culvert that runs partly full holds a circular segment of liquid, exactly like a tank lying on its side. Use the segment formula on the page about partly filled horizontal cylinders: a 12 in pipe running half full holds half of 5.8752, or 2.94 gallons per foot. Larger vessels follow the same formula as a pipe; the cylinder tank volume calculator covers vertical and horizontal tanks with their depth gauge.
A pipe or tube can also be used as a form and filled with concrete. In that case you need the volume in cubic feet or yards and the number of bags: see the concrete cylinder calculator.
Common mistakes
- Nominal size as the diameter. Use the measured or published inside diameter.
- Diameter used as the radius. The result is four times too large.
- Feet and inches mixed. d² × 0.0408 already contains the 12 in per foot: enter d in inches and L in feet. With π × r² × L, put both in inches.
- US and UK gallons. Divide liters by 4.54609 for UK gallons and by 3.785411784 for US gallons. The page on cylinder volume in gallons lists all the factors.
Rule of thumb: a 1 in bore holds about 4 gallons per 100 ft. Multiply by the square of the bore for other sizes: 2 in holds 4 × 4 = 16 gallons per 100 ft.
FAQ
How do you calculate the volume of a pipe?
Measure the inside diameter d and the length L in the same unit, then compute V = π × d² × L ÷ 4 (or π × r² × L with the radius). A pipe with a 2 in inside diameter and 100 ft long holds π × 1² × 1,200 = 3,769.9 in³, which is 16.32 US gallons.
How many gallons of water are in a foot of pipe?
Multiply the square of the inside diameter in inches by 0.0408. A 1 in bore holds 0.0408 gallons per foot, a 2 in bore 0.1632, a 4 in bore 0.6528 and a 6 in bore 1.4688. The factor comes from π ÷ 4 × 12 ÷ 231 = 0.040800.
Should I use the inside or outside diameter of the pipe?
The inside diameter, for the water a pipe holds. The nominal size printed on a pipe is a name, not a measurement, and the outside diameter includes the wall. Measure the bore or take the inside diameter from the maker's data for your exact pipe.
How do I find the diameter of a pipe from its volume?
Rearrange the formula: d = √(4V ÷ (π × L)). For 10 US gallons (2,310 in³) in 50 ft (600 in) of pipe, d = √(4 × 2,310 ÷ (π × 600)) = 2.21 in.
How long does it take to fill a pipe?
Divide the pipe volume by the flow rate. 100 ft of 2 in pipe holds 16.32 gallons; at 4 gallons per minute it fills in about 4.1 minutes.
What is the volume of a 6 ft pipe with a 2 inch inside diameter?
π × 1² × 72 = 226.19 in³, which is 0.979 US gallons or 3.71 liters.
Related
- Cylinder tank volumeTank volume calculator for vertical and horizontal cylinder tanks, full or partly filled. Get the capacity in gallons and liters, with worked examples.
- Hollow cylinderThe volume of a hollow cylinder is V = π(R² − r²)h. Find the material in a tube or pipe wall from radii, diameters or wall thickness, with worked examples.
- Cylinder volume in gallonsFind the volume of a cylinder in gallons: π × r² × h in inches ÷ 231, or in feet × 7.48052. US and imperial gallons, worked examples and a capacity chart.
Updated October 12, 2026