Volumetric Flow Rate Calculator

At a glance:Volumetric flow rate (symbol Q) is 'the volume of fluid passing a cross-section per unit time', in cubic metres per second (m³/s). It is the most basic and common quantity in hydraulics, irrigation and water supply. From the continuity equation: Q=A×v, where A is the cross-sectional flow area (m², the area actually occupied by the flow) and v is the average velocity over that section (m/s). It is intuitive: imagine a column of water advancing at speed v — the volume pushed through area A each second is 'base area × distance travelled' = A×v. Details: A is the flow area perpendicular to the flow — for a full circular pipe A=π·D²/4 (D diameter); for a rectangular open channel A=b·y (b bottom width, y depth); for partly-full pipe or irregular channel, use the geometry at the water level. v is the average velocity — because real velocity is non-uniform across a section (slow at walls, fast at centre), we use the mean so that A·v equals the true flow. A key corollary of continuity: for incompressible flow (water), flow is conserved along the pipe, A₁v₁=A₂v₂, so a narrower section flows faster (nozzle) and a wider one slower. Example: A=0.05 m², v=2 m/s → Q=0.05×2=0.1 m³/s (100 litres per second). Uses: (1) flow estimation for supply/irrigation and pump selection; (2) sizing pipe and channel sections (from required Q and allowable v, back-calculate A); (3) accounting sprinkler/drip water use; (4) with continuity, analyse velocity change in variable-diameter pipes. Notes: (1) use the actual flow area — for partly-full pipe or open channel compute by water level, not the whole pipe cross-section; (2) v is the average velocity; if you have the centre (max) velocity, convert to average first; (3) keep units consistent (A m², v m/s → m³/s; ×1000 for L/s, ×3600 for m³/h); (4) this applies to steady incompressible flow. In short, volumetric flow rate follows Q=A·v — the core formula for pipe, channel and irrigation flow estimation.