Hose Flow Rate Calculator — Water Flow Estimate

UK mains water pressure is typically 1-4 bar, with 3 bar being common. Water companies must supply a minimum static head of around 1 bar (7m) at the boundary stop tap. Check with a pressure gauge on an outside tap, or ask your supplier.

Yes, strongly. Friction loss rises with length, so flow falls off as roughly the inverse 0.54 power of length (Hazen-Williams). In practice doubling the hose length cuts flow by about 30%, and a 100m hose delivers little more than half the flow of a 25m hose of the same bore. For long runs, larger-bore hose or a fixed irrigation pipe keeps more pressure.

12.5mm (1/2 inch) is the standard bore and suits most gardens, giving roughly 25 L/min at 3 bar over 25m with the hose end open. Step up to 19mm (3/4 inch) for large gardens, long runs, or feeding multiple sprinklers - its larger bore can more than double the flow because flow scales with diameter to the 2.63 power.

Run the hose into a 10-litre watering can or bucket and time how long it takes to fill. Divide 10 by the seconds, then multiply by 60 for litres per minute (for example, 40 seconds to fill 10L = 15 L/min). A bucket test beats any calculation because it captures your real tap, fittings, and bends.

This calculator assumes the hose end is open to the air so the full supply pressure is lost to hose friction, which tends to over-estimate. Quick-connect fittings, nozzles, kinks, bends, and a partly open tap all add resistance and lower the true flow. Treat the figure as a sizing guide and confirm with a bucket test.