About the Pipe Volume Calculator
This pipe volume calculator works out how much liquid fits inside a length of pipe, tube or hose. Enter the inside diameter and the length in the units you have — inches and feet, or millimetres and metres — and it returns the capacity in US gallons, litres, cubic feet and cubic metres, the capacity per foot and per metre, and the approximate weight of the water it holds.
Plumbers use it to estimate how long it takes to get hot water to a tap or how much antifreeze a heating loop needs; irrigation and pool installers use it to size fill volumes; engineers use it for flushing, pressure-test and chemical-dosing volumes. If you also enter a wall thickness, the calculator treats the pipe as a hollow cylinder and gives the outside diameter and the volume of pipe material, which you can multiply by density to get the pipe’s own weight.
Use the actual inside diameter, not the nominal pipe size: a “1-inch” pipe can have an inside diameter anywhere from about 0.8 to 1.1 inches depending on the material and schedule, which changes the volume noticeably.
With the default inputs, the capacity is 16.32 US gal. Change any value above to recalculate instantly.
How to use the pipe volume calculator
- 1Measure or look up the pipe’s inside diameter and choose its unit.
- 2Enter the total length of the run and its unit.
- 3Optionally enter the wall thickness to get the outside diameter and material volume.
- 4Read the capacity in gallons and litres, plus the per-foot and per-metre figures.
Formula and method
The inside of a pipe is a cylinder, so its volume is the cross-sectional area π r² (with r half the inside diameter) multiplied by the length. The calculator converts both dimensions to metres first, so you can mix units — an inside diameter in inches with a length in feet, or millimetres with metres — and then converts cubic metres to litres (× 1,000), US gallons (1 gal = 3.785411784 L) and cubic feet (1 ft³ = 0.028316846592 m³).
Water weight assumes fresh water at about 20 °C (0.9982 kg per litre, about 8.33 lb per US gallon). For a hollow cylinder the outer radius is R = r + wall thickness, and the material volume is the difference between the outer and inner cylinders, π(R² − r²)L, reported in cubic centimetres.
- d
- Inside diameter
- r
- Inside radius (d ÷ 2)
- R
- Outside radius (r + wall thickness)
- L
- Pipe length
Worked examples
100 ft of 2-inch pipe
r = 1 in and L = 1,200 in, so V = π × 1 × 1,200 ≈ 3,769.9 in³. Dividing by 231 in³ per gallon gives about 16.32 US gallons (61.78 L), which weighs roughly 136 lb.
50 m of 100 mm pipe
r = 0.05 m, so the cross-section is π × 0.0025 ≈ 0.007854 m² — 7.854 L per metre. Over 50 m that is about 392.7 L, or 103.7 US gallons.
20 ft of 6-inch pipe with a 0.5-inch wall
The inside holds π × 9 × 240 ÷ 231 ≈ 29.38 gallons (about 1.47 gal per foot). With a 0.5-inch wall the outside diameter is 7 in and the wall material is π × (3.5² − 3²) × 240 ≈ 2,450.4 in³, or about 40,156 cm³.
Frequently asked questions
How do you calculate the volume of a pipe?+
Multiply π by the inside radius squared and by the length: V = πr²L, with all dimensions in the same unit. Then convert cubic units to gallons or litres.
How many gallons are in a foot of pipe?+
Gallons per foot ≈ 0.0408 × d², where d is the inside diameter in inches. A 1-inch pipe holds about 0.041 gal/ft, a 2-inch pipe about 0.163 gal/ft and a 4-inch pipe about 0.653 gal/ft.
Should I use the inside or outside diameter?+
Use the inside diameter for fluid capacity. The outside diameter only matters for the pipe material volume, insulation or clearance. Nominal sizes are neither exactly, so check the manufacturer’s inside diameter.
How much does the water in a pipe weigh?+
Fresh water weighs about 8.33 lb per US gallon or 1 kg per litre. 100 ft of 2-inch pipe holds about 16.3 gallons, so roughly 136 lb of water.
What is the volume of a hollow cylinder?+
Subtract the inner cylinder from the outer one: V = π(R² − r²)L, where R is the outer radius and r the inner radius. That gives the volume of the wall material.