What Are the Dimensions of A Fire Hydrant?

Dimensions of A Fire Hydrant

When a building is ablaze, we don’t have to hand over buckets of water to the next person before pouring it on the flames. Instead, firefighters connect their hoses to fire hydrants to put the flames out in hardly any time at all. But have you ever wondered how large a fire hydrant is?

A typical wet barrel fire hydrant stands between 4 and 5-1/4 feet tall, with the barrel measuring about 19 inches in diameter.

In this guide, I’ll explain the various types of fire hydrants, their dimensions, and how a fire hydrant works.

Types of Fire Hydrants

Types of Fire Hydrants

Fire hydrants are categorized by the availability of water inside the barrel—i.e., the shaft-like section that juts out of the ground. There are two main types of fire hydrants in this case: wet barrel and dry barrel.

Wet Barrel

A wet barrel fire hydrant is the more common of the two main types. Water from underwater supply lines is continually gushing upward through the fire hydrant, but the valves, which remain closed when the fire hydrant is unused, prevent the water from seeping out. The moment a firefighter or maintenance worker opens the valve to alleviate built-up pressure, water from the supply line will immediately come out at a rate of at least 500 gallons per minute.

This type of fire hydrant, which can remain usable for upwards of a century with proper maintenance, is more common in places where freezing isn’t a possible risk. If this type of fire hydrant was found in a place like, say, St. Paul, Minnesota, where temperatures can drop to 12°F in the winter, then the water inside the fire hydrant would freeze, rendering the hydrant system unusable for months at a time.

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Dry Barrel

The barrel of a dry barrel fire hydrant remains dry when it’s not in use. Water is flushed out of the fire hydrant via a drain valve whenever the main valve is shut. When the main valve is disengaged via the top-facing stem nut, water from the supply line, which is located underground and below the frost line, comes gushing upward and through the operating stem.

Essentially, a dry barrel remains dry whenever it’s not used. Unlike wet barrel fire hydrants, dry barrels are not filled with pressurized water 24/7. It’s only when a firefighter opens up the underground water supply line that water will begin pouring out of the fire hydrant.

This sort of system is ideal in places where temperatures drop to below freezing. If the water were to stay inside the cast-iron or brass barrel, it would not only prevent firefighters from fighting fires, but the water would also expand and cause damage to the operating stem.

Parts of a Fire Hydrant

Parts of a Fire Hydrant

Before talking about the dimensions of a fire hydrant, it’s important that we first understand what a fire hydrant consists of.

Bonnet—The domed top of a fire hydrant where the stem or operating nut is located.

Stem/Operating Nut—The main port that is used to open and shut the main valve and bring up through the operating stem and into the barrel.

Main Valve—The underground valve that opens and shut to allow water from the supply line into the barrel.

Barrel—The standpipe section is made of cast iron, brass, or another durable metal. It houses all of the internal components, including the main valve and the operating stem.

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Drain Hole—The underground port that allows water inside the barrel to drain. Pressurized water from the supply line will cause the drain hole to seal. When pressure is alleviated, the drain holes will automatically open, letting water flow into the surrounding soil.

Operating Stem—The pipeline that directs water from the water supply line, when opened, to the pumper nozzle.

Pumper Nozzle—The exterior section of a fire hydrant where a hose is connected to redirect water.

What Are the Dimensions of a Fire Hydrant?

What Are the Dimensions of a Fire Hydrant

In terms of appearance and dimensions, there is virtually no difference between the wet barrel and dry barrel fire hydrants. They will both stand roughly 4 to 5-1/4 feet above the surface of the ground and measure roughly 19 inches in diameter around the barrel.

However, the figures above only describe the sections of a fire hydrant that we can see. The chart below will describe the technical specifications of a fire hydrant from the inside and out.

Height above ground level4 to 5-1/4 feet
Barrel Diameter19 inches
Buried Depth3 to 10 feet
Hose Connection2.5 inches
Thread Size7.5 threads per inch
Stem Nut Diameter7/8 inches
Operating Stem Diameter4 to 16 inches

The Meaning Behind Fire Hydrant Colors

The most common fire hydrant color is yellow. It’s brightly colored to increase its visibility, so motorists will have an easier time seeing the fire hydrant when looking for a safe place to park.

According to the NFPA (National Fire Protection Association) 291, there are four distinct fire hydrant bonnet and/or cap colors:

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Blue (Class AA)—1,500+ GPM

Green (Class A)—1,000 to 1,499 GPM

Orange (Class B)—500 to 999 GPM

Red (Class C)—Less than 500 GPM

What Water Do Fire Hydrants Use?

All fire hydrants are connected to a water company’s supply line. That means the water that firefighters use to douse flames is the same water you drink from the tap or use to shower. However, if you’re thirsty or if you want to soak your body in fresh water, don’t tap a fire hydrant. It’s not just incredibly dangerous, but it’s also illegal!

However, there is a uniquely colored fire hydrant that someone uploaded to Reddit. Violet fire hydrants, which are quite rare, are connected to sources of non-potable water—i.e., water that is not safe to drink since it has not been treated. Sources of non-potable water include natural bodies of water, such as lakes and ponds.

Can I Remove Fire Hydrants?

No, you cannot. First and foremost, fire hydrants, while on public property, are maintained by the city and/or water companies. In addition, removing a fire hydrant doesn’t just involve lifting the 800-pound structure, but you also have to shut off the water supply line, which even the most hardcore DIYers might be ill-equipped to do.


Baron Cooke has been writing and editing for 7 years. He grew up with an aptitude for geometry, statistics, and dimensions. He has a BA in construction management and also has studied civil infrastructure, engineering, and measurements. He is the head writer of measuringknowhow.com

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