Work out how many litres of water a run of pipe holds from its internal diameter and length — handy for flushing, disinfection dosing and pressure testing.
traqR keeps plumbing jobs, commissioning notes and certificates together on the site record. Try it free for 14 days.
Start free trialThe cross-sectional area of a round pipe is π × (internal radius)². Use the actual bore, since nominal size and internal diameter differ.
Multiplying the bore area by the pipe length gives the internal volume, which converts to litres.
Knowing the volume tells you how much water to flush, how much chemical to dose for disinfection, or how long a line takes to clear.
Work out the bore area — π × (internal diameter ÷ 2)² — then multiply by the length. A 20 mm bore pipe holds about 0.314 litres per metre, so a 50 m run holds roughly 15.7 litres. This tool does the conversion for you.
It’s needed for flushing and disinfecting new or repaired mains (to work out chlorine dosing and contact time), for estimating how long it takes to clear a line, and for filling and pressure-testing. It also helps size expansion and dead-leg concerns.
Use the actual internal diameter. Nominal size (DN) is a label, and the real bore varies with the pipe’s material and pressure class. For accurate volume, take the internal diameter from the manufacturer’s data.
Yes, for round pipes running full of water. Just enter the internal diameter and length. For part-full drains or non-circular sections the calculation differs.
This calculator gives the internal volume of a round pipe running full, based on the bore you enter. Use the actual internal diameter for accuracy. For disinfection, testing and plumbing work, follow AS/NZS 3500 and your water authority’s requirements.
traqR keeps plumbing jobs, commissioning notes and certificates together on the site record. Try it free for 14 days.