How Many Millimeters Is A Garden Hose? | Common Hose Sizes

Guide / By

Most garden hoses measure about 13 mm, 16 mm, or 19 mm inside, with 16 mm matching the common 5/8-inch hose.

If you’re trying to match a nozzle, replace an old hose, or buy the right splitter, millimeters can trip you up. Garden hoses are often sold in inches in the U.S., yet many labels, fittings, and imported products use millimeters.

The fix is simple once you know what part is being measured. In most cases, a garden hose size refers to its inside diameter, not its outside width. That one detail clears up most of the confusion.

For a fast reference, the common conversions are:

  • 1/2 inch = 12.7 mm
  • 5/8 inch = 15.875 mm
  • 3/4 inch = 19.05 mm

In store listings, those numbers are often rounded to 13 mm, 16 mm, and 19 mm. So if a package says 15 mm or 16 mm, it’s usually pointing to a 5/8-inch garden hose.

What Garden Hose Size Actually Means

When people ask how many millimeters a garden hose is, they’re usually asking about the hose bore. That’s the open space inside the hose where water flows.

This matters because two hoses can look close in outer width and still have different flow rates. One may have thicker walls, which changes the outside measurement while leaving the inside diameter smaller.

That’s why hose size is not the same thing as fitting size. A standard garden hose fitting in the U.S. is often 3/4-inch thread, even when the hose itself is 1/2 inch or 5/8 inch. People mix those two numbers all the time, then end up ordering the wrong part.

Why Millimeters Show Up On Garden Hose Labels

Many hose makers sell into more than one market, so product pages and packaging may show both inch and metric sizes. European brands often lead with millimeters, while U.S. brands lean on inch fractions.

That’s not a different sizing system. It’s the same hose, just written two ways.

Garden Hose Millimeters By Common Size

The exact inch-to-millimeter conversion comes from NIST conversion guidance, which uses 25.4 millimeters per inch. Once you apply that number, the usual garden hose sizes fall into a neat pattern.

Common garden hose sizes in mm

  • 3/8 inch = 9.525 mm
  • 1/2 inch = 12.7 mm
  • 5/8 inch = 15.875 mm
  • 3/4 inch = 19.05 mm
  • 1 inch = 25.4 mm

For everyday home watering, the sizes you’ll see most are 1/2 inch, 5/8 inch, and 3/4 inch. A 1-inch hose exists, though it’s more common in heavy-duty or commercial setups than around a backyard spigot.

A good rule is this: if the label says 13 mm, think 1/2 inch; if it says 16 mm, think 5/8 inch; if it says 19 mm, think 3/4 inch.

Which size is most common

For many households, 5/8 inch is the sweet spot. It moves more water than a 1/2-inch hose without getting as bulky as a 3/4-inch line. You’ll see that reflected across many retail and brand listings, including products from Gilmour’s garden hose range, which offers 1/2-inch, 5/8-inch, and 3/4-inch options.

That said, the “best” size depends on hose length, water pressure, and what you’re doing at the other end. A short hose filling watering cans has different needs than a long hose feeding a sprinkler across a big lawn.

How Many Millimeters Is A Garden Hose In Real Buying Terms?

Here’s where the numbers become useful. You’re not just converting fractions into metric. You’re matching size to the job.

If a listing says 12.5 mm, 13 mm, 15 mm, or 19 mm, it’s telling you how much room water has to move through the hose. More room usually means more flow, though length and pressure still matter.

Hose Size Millimeters What It’s Often Used For
3/8 inch 9.5 mm Light watering, small specialty lines
1/2 inch 12.7 mm Patios, short runs, light yard work
5/8 inch 15.9 mm Most home gardens and general watering
3/4 inch 19.1 mm Large yards, stronger flow, faster filling
1 inch 25.4 mm Farm, commercial, or heavy water demand
13 mm label Rounded metric size Usually sold as 1/2 inch
16 mm label Rounded metric size Usually sold as 5/8 inch
19 mm label Rounded metric size Usually sold as 3/4 inch

That last group matters more than it may seem. Some brands round to the nearest whole number, while others use the cleaner metric name right on the front of the box. A 16 mm hose is not a strange size. It’s usually just a 5/8-inch hose written for a metric-friendly catalog.

How Hose Diameter Changes Water Flow

Bigger diameter usually means more water can move through the hose at once. That helps when you’re running a sprinkler, washing a car, or trying to keep pressure from dropping across a long run.

FITT’s official hose size guide makes the same point: diameter affects flow rate, and longer hoses add resistance. So a 1/2-inch hose may feel fine at 25 feet, then feel weak at 100 feet.

Small hose vs larger hose

A 1/2-inch hose is lighter, easier to coil, and easier to drag around corners. That makes it handy for small spaces or short watering sessions.

A 5/8-inch hose is the common middle ground. It gives you more flow without getting too heavy. For many yards, that’s the most balanced pick.

A 3/4-inch hose shines when you want volume. It’s handy for long runs, larger sprinklers, and jobs where waiting on water gets old fast. The tradeoff is weight, plus a stiffer feel when full.

Garden Hose Size Vs Fitting Size

This is where plenty of buying mistakes happen. The hose diameter and the connector thread are not the same measurement.

Your hose may be 1/2 inch or 5/8 inch inside, yet still attach to a standard outdoor faucet with a 3/4-inch garden hose thread connection. So if your nozzle says it fits a 3/4-inch garden hose connection, that does not mean you need a 3/4-inch bore hose.

Read the packaging with that split in mind:

  • Hose size = water path inside the hose
  • Fitting size = threaded connector at the end

Once you separate those two, hose shopping gets a lot less messy.

What You’re Measuring Typical Number Why It Matters
Inside diameter 13 mm, 16 mm, 19 mm Controls flow through the hose
Outside diameter Varies by wall thickness Not the main buying size
Fitting thread Often 3/4 inch Controls what the hose connects to

How To Measure Your Existing Hose

If you already own a hose and want the metric size, the cleanest method is to measure the inside diameter. A ruler can work in a pinch, though calipers give a neater reading.

  1. Cut the water and empty the hose.
  2. Look at the open end of the hose, not the metal connector.
  3. Measure the inside width straight across.
  4. Match it to the nearest common size: 13 mm, 16 mm, or 19 mm.

If you measure close to 16 mm, you almost surely have a 5/8-inch hose. If the number lands near 13 mm, it’s a 1/2-inch hose. If it lands near 19 mm, it’s a 3/4-inch hose.

Don’t panic if the reading is off by a hair. Rubber, vinyl, and reinforced hose walls can flex a little, and many consumer labels round the metric number anyway.

Which Garden Hose Size Makes Sense For Your Yard

If your yard is small and your hose run is short, a 13 mm or 1/2-inch hose will usually do the job. It’s lighter in the hand and easier to store.

If you want one size that covers most normal chores, 16 mm or 5/8 inch is the safe bet. It works well for hand watering, spray nozzles, and many sprinklers without feeling bulky.

If you’re feeding a larger sprinkler, covering a wider yard, or hauling water across a long distance, 19 mm or 3/4 inch can be worth the extra heft.

So, how many millimeters is a garden hose? Most of the time, the answer is one of three numbers: 13 mm, 16 mm, or 19 mm. For many homes, 16 mm is the one you’ll see most often.

References & Sources

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