Though the number varies based on a number of factors, which we’ll get into more below, the average gallon per minute (GPM) flow rate of a standard garden hose is 17.4 gallons per minute. That’s assuming a 5/8″ garden hose that is 50 ft. in length with 50 PSI of water pressure. That is the size of what we think is the best garden hose on the market for most people.
- What is GMP and How is it Determined?
- Determining GPM Garden Hose Flow on Your Own
- A Helpful Video on Calculating GPM Flow Rate
- Flow Rate of Outdoor Spigot
- Factors That Effect GPM in a Garden Hose
- Useful Video on How to Measure the Diameter of a Garden Hose
- How to Determine PSI in a home?
What is GMP and How is it Determined?
GPM is the flow rate of water through a pipe or hose measured in gallons per minute. Determining it is simply a mathematical function of the dimeter of your hose, the length of your hose, and the water pressure flowing through your home’s pipes. In fact there’s a handy website that will do the GPM equation for you.
However, in order to get an exact GPM for your garden hose using this equation, you need to have exact inputs. For some people that’s challenging as they don’t remember the size of the hose they bought and don’t know the water PSI in their home.
Determining GPM Garden Hose Flow on Your Own
If you’re unsure of one or more of your inputs – hose length, hose diameter, water PSI – a great way to determine the GPM of your garden hose is to time the flow rate yourself. To do so, find a 5 gallon bucket and a stop-watch (most phones have them in the clock app). Turn the water on your hose bib to full blast and see how long it takes to fill up the bucket. Once you have that information, you have the flow rate. It’s now just a matter of converting your data to gallons per minute.
For instance, if it takes 30 seconds to fill a 5 gallon bucket, you have a 10 GPM flow rate in your garden hose.
A Helpful Video on Calculating GPM Flow Rate
The equation above was simple. 30 seconds for 5 gallons is easy to convert, most people can do that in their hear. More than likely you’ll have to do a little math to determine your GPM, but don’t worry! It’s pretty easy math. Here’s what your do:
Divide 60 by the seconds it takes to fill up your 5 gallon bucket and multiply it by 5. That’s it!
For those of you that like a mathematical equation, here’s what that looks like:
X = Seconds to fill up 5 gallon (G) bucket
60 = seconds in 1 minute (M)
Y = Gallons Per Minute (GPM)
Y = (60 ÷ X) x 5
For example, say it takes 23 seconds to fill your 5 gallon bucket. Plugging that into the equation above, you get a GPM of 13.04
Determining Garden Hose Flow Rate in Liters
If you’re looking for the flow rate in liters, you can go about that one of two ways: 1) You can find a 5 liter container and do the exact experiment above. 2) Or you can calculate the GMP flow rate then simply convert gallons to liters, which you can do here.
Flow Rate of Outdoor Spigot
You can do the same experiment as you did above with the 5 gallon bucket if you can. However, many hose bibs are low to the ground, which can make it difficult or impossible to fill a 5 gallon bucket with.
Flow rate of an outdoor spigot low to the ground
So how do you determine the flow rate for a garden hose spigot that’s only a foot or less above the ground? You’ll need to find the largest container you can find that fits under that hose bib and determine it’s volume. First look to see if the container has its volume printed or stamped onto it somewhere. Usually that will be on the bottom or on its outside shell somewhere.
If you can’t find it the volume printed on the container, you can take a container you know the volume of, ideally that will be a 1 gallon container and fill it with water. Empty your gallon container into the other, shallow container as many times as possible without over-flowing. Take note on how many times you had to re-fill your gallon container. Let the water in the shallow container settle, then place a piece of tape marking the water line.
You now have a volume measurement of the shallow container, which will enable you to conduct the same experiment above. Instead of multiplying by 5, however, you’ll need to multiply by the gallon measurement in the shallow container.
Factors That Effect GPM in a Garden Hose
As mentioned above, there are 3 factors that can change the rate of flow in your garden hose, which can be plugged into the tool on this page: hose length, hose diameter, and PSI. So how do you determine these inputs?
This is an easy one, especially if you can locate the receipt for your hose or recall the length you selected when you bought it. Garden hoses are manufactured at a variety of length, the most common being 25 ft, 50 ft, and 100 ft.
If you’re unsure what length your garden hose is, simply lay it out in your yard and measure it with a measuring tape.
Garden hose diameters range between 1/2″ to 1″. The most common household garden hoses are 1/2″ and 5/8″. If you’re unsure, you can measure itself by measuring the diameter of the inside of the hose.
Do this by rolling up an index card tightly as possible, fitting it into the garden hose as deeply as possible. Let it expand and measure the diameter of the circle it creates. Remember it’s the inside of the rubber part, not the metal fitting that determines the garden hose’s diameter.
If it’s an old hose, you may find the diameter may not be the same as when you bought the hose. That’s because the inside of is greatly affected by the condition of the hose itself. As the hose ages, the diameter may expand as the inner lining of the hose deteriorates.
Useful Video on How to Measure the Diameter of a Garden Hose
How to Determine PSI in a home?
The average PSI in homes is around 50 nationwide, but it varies between municipalities, your neighborhood’s geography, the quality of the plumbing in your area, and how water is generally being used around you by neighbors. If would not be unusual if you found that the PSI in your water pipes is 35 or even 80.
One way to check your PSI is to contact your city’s water district office. They should be able to tell you what the PSI of the water is in your city on average. This will vary between municipalities based on the equipment it is using to pump water out of the facility, amongst other factors.
Is your home up or down a hill? If the water has to flow uphill, it will generally flow with less force upon entering your home, resulting in lower PSI, than if it is flowing downhill, which would increase the PSI of your water-flow.
Quality of Plumbing
If you live in a city that was built a long time ago, chances are the plumbing has some issues. If there are leaks in the pipes somewhere in the city, that can affect the waster pressure in your home, even if the leaks aren’t actually in your home.
General Water Use
If you have neighbors who use an unusual amount of water, whether that be a household or a large factory nearby, that will also affect the water pressure in your home. If a fire hydrant has broken or the fire department is using a fire hydrant to fight a large fire, that can also be a factor. Any time a large amount if water is being used, some of the pressure is being diverted to accomadate that usage, lowering the PSI in your home.
Using a Gauge to determine PSI
The best way to determine your home’s water PSI is to buy gauge at your local hardware and measure it yourself. As mentioned earlier, you can contact your local water district office and they’ll be able to tell you the PSI leaving the plant, and even the average household PSI in your area. But they won’t be able to account for the factors mentioned above – the geography your home sits on, etc.
We determined the average GPM of water-flow in a garden hose to be 17.4, but as you can see there are so many factors that can change that figure. Do your best to determine your hose size, both in diameter and length. Then find find out what the PSI of the water flow is in your house. Once you have those three figures you can find out your GPM here (link).
An even easier method for most people is to simply time how long it takes to fill up a 5 gallon bucket of water.