What is typical UK mains water pressure?

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.

Does hose length affect flow rate?

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.

What size garden hose is best?

12.5mm (1/2 inch) is the standard bore and suits most gardens, giving around 10-15 L/min at 3 bar over 25m. 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.

How do I measure my actual flow rate?

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.

Why might my real flow be lower than the estimate?

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.

GardenCalcs

Hose Flow Rate Calculator — Water Flow Estimate

Estimate water flow rate based on hose diameter and pressure.

Hose DiameterInternal bore: 12.5mm (1/2 inch) is standard; 19mm (3/4 inch) flows far more for long runs or sprinklers.

Hose Length

Total run from tap to nozzle. UK reels are typically 25-50m; longer runs lose noticeable pressure.

Water Pressure

Static supply pressure at the tap. UK mains is usually 1-4 bar; 3 bar is a common default.

How We Calculate This

Flow rate is estimated with the Hazen-Williams garden-hose equation, which relates flow to the hose internal diameter, supply pressure, and length: a larger bore raises flow steeply (to the 2.63 power of diameter) while extra length reduces it (to the inverse 0.54 power).

It assumes the hose end is open to atmosphere, so the entire supply pressure is dissipated by friction along the hose. A roughness coefficient C of 135 is used for flexible garden hose (adjustable in advanced options).

Because dynamic pressure actually drops as flow rises, this equation tends to over-estimate. Real flow is also cut by nozzles, fittings, and bends - use a bucket test for an exact figure.

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates based on standard gardening guidelines. Results may vary with soil conditions, climate, and plant varieties.