Garden Hose Flow Rate Calculator

How it works

Hazen-Williams with the full tap pressure lost along the hose: Q = [ head × C^1.852 × D^4.87 ÷ (10.67 × 1.15 L) ]^(1/1.852), C = 140; 1 bar = 10.2 m of head

How much water a hose delivers depends on the pressure pushing it and the friction fighting it, and friction depends fiercely on diameter — a 3/4-inch hose passes roughly twice the water of a 1/2-inch one of the same length — and linearly on length, so a 50 m hose delivers a third less than a 30 m one. The model here treats the hose as a pipe discharging to air with all the tap’s pressure spent on friction (plus an allowance for couplings), which matches bucket-test measurements within 10–20% for hoses in good condition; kinks, cheap couplings and a nozzle cut it further. For filling a pool or a large tank, the diameter and length of the hose matter more than the tap.

Worked example

A standard 5/8″ (15.9 mm) hose, 30 m long, on a 3.5 bar tap: about 44 L/min (12 gpm), so a 1,000 L tank fills in roughly 23 minutes; the same hose at 15 m would give about 64 L/min.

Frequently asked questions