Garden Hose Flow Rate Calculator
Work out how much water a garden hose delivers from its diameter, length and supply pressure. The calculator uses the Hazen-Williams equation, the same method as the PSI to GPM calculator, and returns the flow in US gallons per minute and litres per minute. For charts, measuring tips and the causes of a weak hose, read the garden hose flow rate guide.
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Garden hose flow rateFree download
Get the printable pipe flow chart
Schedule 40 pipe sizes, water flow in GPM and LPM at four design velocities, and recommended velocities by application. One PDF, made to pin above the bench.
How It Works
A garden hose is a smooth-bore pipe, so the flow it delivers follows the same Hazen-Williams relationship as any other pipe run: bore diameter, length and the pressure pushing the water through it. Hose is sold by inside diameter, so the size on the label goes straight into the equation. The roughness coefficient C = 150 is the value for smooth plastic and rubber, the same one the PSI to GPM tool uses for PVC.
The Formula
Q = 0.442 × C × D2.63 × (P / L)0.54
Where Q is the flow in GPM, C = 150 for hose, D is the bore in inches, P is the supply pressure in psi and L is the hose length in feet. Diameter carries the 2.63 exponent, which is why a 3/4" hose delivers roughly twice what a 1/2" hose does at the same pressure.
Worked Example
A 5/8" hose, 50 feet long, on a 50 psi supply:
- • Q = 0.442 × 150 × 0.6252.63 × (50 / 50)0.54
- • Q = 66.3 × 0.2905 × 1
- • Q ≈ 19.3 GPM (72.9 litres per minute)
That is the open-ended figure with no nozzle fitted. A spray gun, a sprinkler or a kinked hose will all give less.
Garden Hose Flow Rate by Size and Pressure
Flow in GPM for a 50 foot hose, open-ended:
| Hose Size | 30 psi | 40 psi | 50 psi | 60 psi |
|---|---|---|---|---|
| 1/2" | 8.1 | 9.5 | 10.7 | 11.8 |
| 5/8" | 14.6 | 17.1 | 19.3 | 21.3 |
| 3/4" | 23.6 | 27.6 | 31.1 | 34.3 |
How Length Cuts the Flow
Flow in GPM at 50 psi supply pressure:
| Hose Size | 25 ft | 50 ft | 100 ft |
|---|---|---|---|
| 1/2" | 15.6 | 10.7 | 7.4 |
| 5/8" | 28.0 | 19.3 | 13.2 |
| 3/4" | 45.2 | 31.1 | 21.4 |
These are open-ended figures with no nozzle. Real hoses run lower: brass couplings, quick-connect fittings, a spray nozzle and any kink all add resistance, and the pressure at the tap drops while the water is running. Treat the table as the ceiling for a given hose, and measure with a bucket to get your own number.
FAQ
Common questions about garden hose flow rates.
How many GPM does a garden hose flow?
A 5/8" hose, the most common size, delivers about 17.1 GPM at 40 psi and 21.3 GPM at 60 psi over 50 feet, open-ended. Double the length to 100 feet and the 50 psi figure falls from 19.3 to 13.2 GPM. A 1/2" hose flows roughly half as much as a 3/4" one at the same pressure and length.
Does hose length reduce flow rate?
Yes, and more than most people expect. Friction along the bore consumes pressure, so a longer hose leaves less pressure to drive the flow. At 50 psi a 5/8" hose gives 28.0 GPM at 25 feet, 19.3 GPM at 50 feet and 13.2 GPM at 100 feet: doubling the length costs roughly a third of the flow each time. Two 50 foot hoses joined together behave as one 100 foot hose.
Is a 3/4 inch hose really worth it over 5/8 inch?
For flow, yes. At 50 psi over 50 feet a 3/4" hose delivers 31.1 GPM against 19.3 GPM for 5/8", about 1.6 times as much, because flow scales with diameter to the power of 2.63 rather than with area. The trade-off is weight and price: a 3/4" hose is noticeably heavier to drag around, which is why 5/8" is the usual domestic choice.
Why is my hose slower than the calculator says?
The calculator gives open-ended flow through the hose alone. In practice a nozzle or spray gun is the main restriction, and it, not the hose, then sets the flow. Couplings, quick-connects, a partly open tap, a kink, and the pressure drop in the house plumbing while the hose runs all take a share as well. The tap pressure to enter is the pressure while the water is flowing, not the static reading.
How do I measure my garden hose flow rate?
Run the hose into a container of known volume and time it. A 10 US gallon (40 litre) bucket filled in 31 seconds is 19.3 GPM; in general, GPM = gallons divided by seconds, times 60. Do it with the tap fully open and the nozzle removed to compare against the table above, then repeat with your nozzle fitted to see what it costs you.
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