Pipe Volume & Flow Calculator

This calculator works out how much water a pipe holds and how fast it can move, two figures that matter for plumbing, irrigation, drainage and water-storage jobs. The volume tells you the capacity of a length of pipe in litres, which is useful for sizing pumps and pressure tanks, working out how long it takes to fill or flush a line, dosing a pipe with chemicals, or estimating how much water sits in a system. The flow rate tells you how much water passes a point each second or minute at a given velocity, which helps you check whether a pipe is big enough for the demand it serves, since a pipe that is too small chokes the flow and a pipe that is too large wastes money and can cause other problems. You enter the internal diameter of the pipe in millimetres, which is the bore the water actually flows through rather than the outside diameter, the length of the run in metres, and a flow velocity in metres per second, and the calculator returns the volume in litres and cubic metres, the cross-sectional area, and the flow rate in litres per second and litres per minute. As a guide, water in household and irrigation pipes typically flows at around 1 to 2 metres per second, with lower speeds preferred to reduce noise, friction loss and wear. Remember to use the internal diameter, because pipe is often described by its nominal or outside size, which is larger than the bore. This is a calculation tool for planning and learning; for pressurised systems and compliance work, follow the relevant standards and a plumber's or engineer's advice.

Use the internal diameter (the bore), not the outside size. Real flow is reduced by friction and fittings. An estimate only.