Pipe Volume Calculator
Find how much water a pipe holds in litres, cubic metres, and gallons from its bore and length.
🚰 What is the Pipe Volume Calculator?
The pipe volume calculator tells you how much liquid a length of pipe holds. Enter the inner diameter and the length, and it returns the internal volume in litres, cubic metres, and US gallons, plus the weight of water the pipe contains. A pipe is simply a long cylinder, so the answer comes from the cylinder volume formula applied to the bore.
This matters in a surprising number of jobs. Plumbers work out how much water sits in a hot-water recirculation loop so they can size a pump. Irrigation designers total the water in a drip network. Pool and aquarium owners account for the volume held in the plumbing, not just the tank. Anyone chlorinating or flushing a new water main needs to know the pipe volume to dose it correctly. In every case the question is the same: how many litres or gallons fit inside this run of pipe.
The single most important rule is to use the inner diameter, not the outer. Only the hollow bore carries water, so the pipe wall must be excluded. Using the outside dimension always overestimates the volume, and the error grows with thicker-walled pipe. Because pipe diameters are usually given in millimetres or inches while lengths are in metres or feet, this calculator gives diameter and length their own unit selectors so you never have to convert by hand.
The tool is useful because it combines the geometry, the unit conversions, and the water-weight conversion in one step. You measure the bore and length, pick the units, and read the volume and weight instantly, with the working shown so you can verify it.
📐 Formula
📖 How to Use This Calculator
Steps
💡 Example Calculations
Example 1 - Single 4-inch pipe, 10 feet long
Example 2 - 50 mm bore pipe, 6 metres long
Example 3 - Three 2-inch pipes, 15 feet each
❓ Frequently Asked Questions
🔗 Related Calculators
How do you calculate the volume of a pipe?
A pipe is a cylinder, so Volume = pi x radius squared x length, where the radius is half the inner diameter. Convert the volume in cubic metres to litres by multiplying by 1,000. A 4-inch (0.1016 m) pipe that is 10 feet (3.048 m) long holds pi x 0.0508 squared x 3.048 = 0.0247 cubic metres, about 24.7 litres.
Should I use the inner or outer diameter of the pipe?
Always use the inner (bore) diameter. Only the hollow inside of the pipe holds water, so the pipe wall must be excluded. Using the outer diameter overstates the volume, and the error grows with thicker walls. If you only know the nominal size, look up the internal diameter for that pipe schedule.
How much water does a pipe hold per metre?
It depends on the bore. Volume per metre = pi x radius squared x 1 m. A 50 mm (0.05 m) inner-diameter pipe holds pi x 0.025 squared = 0.00196 cubic metres per metre, which is about 1.96 litres per metre. Doubling the diameter quadruples the volume per metre.
How do I convert pipe volume to gallons?
Calculate the volume in cubic metres, then multiply by 264.17 to get US gallons. For example, a pipe holding 0.0247 cubic metres contains about 6.5 US gallons. To get litres instead, multiply the cubic-metre figure by 1,000.
How much does the water in a pipe weigh?
Water has a density of about 1 kilogram per litre, so the weight in kilograms is essentially equal to the volume in litres. A pipe holding 24.7 litres of water carries about 24.7 kg of water. This calculator reports that weight directly alongside the volume.
Why does the calculator have separate units for diameter and length?
Pipes are almost always specified with the diameter in millimetres or inches and the length in metres or feet. Forcing a single unit would make you convert one of them by hand. Separate selectors let you enter each measurement in its natural unit, and the calculator handles the conversion.
How do I calculate the total volume of a piping system?
For several identical lengths of the same pipe, set the pipe count to the number of runs and the calculator multiplies the single-pipe volume accordingly. For a system with different diameters, calculate each size separately and add the results together.
Does pipe volume depend on the material?
No. The internal volume depends only on the bore diameter and length, not on whether the pipe is PVC, copper, steel, or PEX. Material affects wall thickness, which is why you should always measure or look up the internal diameter rather than the outside dimension.
How accurate is the pipe volume calculation?
The formula is exact for a straight cylindrical pipe with a constant bore. Fittings, bends, valves, and internal scaling change the real volume slightly. For most plumbing and irrigation estimates the straight-pipe figure is accurate to within a few percent.
How much water is in 100 feet of 1-inch pipe?
A 1-inch (0.0254 m) bore pipe holds pi x 0.0127 squared per metre, about 0.507 litres per metre. Over 100 feet (30.48 m) that is roughly 15.4 litres, or about 4.1 US gallons. Enter 1 inch diameter and 100 feet length to confirm the figure for your exact pipe.