DonyRony LOGO

Brass Fitting Sizes: How to Measure Brass Fittings

measuring brass fittings using a caliper

How do you measure brass fitting sizes? When it comes to fittings, dimensions can be confusing, what with the variation in metrics and the so called nominal and inner or outer diameters. Not to worry, though. In this brass fittings size guide, we show you how to measure brass fittings and match them with the right tubing or pipe diameters.

How do you Determine Your Fitting Size?

Knowing how to measure fittings is crucial for ensuring correctly sized plumbing pipes or other tubing. Wrongly matched pipes and fittings lead to weak joints and leaking lines, and should be avoided at all costs.

To measure the size of pipe fittings, you need to understand the industry terms for their dimensions. These include nominal size, outside diameter, and inside diameter.

  • Nominal Size– denoted by DN, this a number used for pipe size reference. Note that this number does not represent pipe actual diameters but their approximations.
  • Outside Diameter– used to indicate the fitting size when measured externally across its end.
  • Inside diameter– measured in the same way as outside diameter but this time from the inner edges.
Different brass fitting sizes and types illustrated
Different brass fitting sizes and types illustrated

Brass Fitting Sizes

These are fittings made from a type of alloy called brass. With characteristic yellow or golden colors, brass fittings are common across different applications (plumbing or water lines, gas line, and other commercial or industrial settings).

These pipe fittings are designed in many different dimensions, with the most popular being 1/4”, 3/8”, 1/2”, and 3/4”. These are mostly meant for residential applications. Larger brass fitting sizes for commercial and industrial installations are also available.

Besides size, brass fittings are sold in a range of configurations. Examples are threaded brass fittings, flare fittings, compression fittings, and barbed hose fittings. Below, we explain how to measure the mentioned types of the fitting.

Measuring brass pipe fitting sizes
Measuring brass pipe fitting sizes

How to Measure Brass Fittings

Knowing how to measure brass fittings allows you to correctly size them for the pipes they will connect to. That in turn, ensures fitting joints that will not leak. Because designs are different, well look at how measure brass fittings based on their different types or configurations.

What you’ll need

  • Thread pitch gauge and IO/ID caliper
  • You can also use a measuring tape or ruler
  • A brass fittings chart

1. Brass Fitting Thread Sizes

Starting with the brass fitting thread sizes, here is what you need to know: fitting threads can be male or female. Male threads are located on the outside of fittings, female thread inside of them. Fitting threads can also be NPT and NPS or, in full, national pipe tapered and national pipe straight.

NPT (National Pipe Tapered): the threaded part assumes a conical shape, which means it tapers or becomes narrower as you move outward. These require Teflon tape or sealing compound to form a leak-free connection or joint.

NPS (national pipe straight): these are non-tapering, which means they maintain the same diameter. They’re normally sealed using O-rings or sealing gaskets and washers. Here’s how to measure brass thread sizes.

  • Determine if you have male or female threads
  • Using a caliper, measure the thread diameter for both ID and OD
  • If you have female thread, measure the inner diameter, which is also abbreviated ID
  • For a female thread, measure the outside diameter or OD
  • Use these measurements to match your fittings with the right pipe on a brass fitting size chart

Note: To determine the distance between threads, place the gauge on the fitting thread until snug and read the measurement.

2. Brass Compression Fitting Sizes

Brass compression fittings form connections using compression sleeves/ferules and nuts. In order to match this type of fitting with a pipe, it’s important that you know how to measure it correctly. Use these steps to determine brass compression fitting sizes.

  • Place the caliper on the inner edges of the fitting
  • Read the inside diameter of the fitting
  • Use this measurement to find a fitting pipe size on a sizing chart
  • When sizing a tube or pipe for the compression fitting, take the pipe’s OD dimensions

3. Brass Flare Fitting Sizes

Brass flare fittings are used in high-pressure lines and are mostly found in gas distribution systems. Just like when measuring other brass fitting sizes, you need a measuring tool to take the measurements.

  • Place a caliper on the widest point of the flare fitting thread
  • Measure the thread diameter at this point.
  • Using a measurements chart, compare or match your brass flare fitting sizes
  • The chart will provide the corresponding tube sizes that will ensure a proper connection or joint.

4. Brass Barbed Hose Fitting Dimensions

A brass barbed hose fitting is a type of fitting that’s meant for use with a soft pipe. So you normally use it in low-pressure lines or applications. Just as its name suggests, it features barbs that serve as grippers to make the fitting hold onto the tubing. To measure brass barbed hose fitting dimensions, use these steps:

  • Measure the fittings ID, or inner diameter in full, but at the barbed end.
  • That means the fittings barbed section will be larger than the hose that it will connect to.
  • As an example, if your barbed fitting measures 3/8, you need a soft tube that measure 3/8 for ID.
  • Avoid using a hose larger than the barbed fitting, as the fitting will not hold.

Pipe Size in Inches

Nominal Size

Female Thread ID

Male Thread OD





























Brass compression fitting size chart

Brass Fittings Size Chart

After measuring brass fitting sizes, the next step is to find the right pipes or hose sizes to use with them. One of the ways to do is by using a sizing chart. This a chart that allows you to match your brass fitting dimensions with those of the required tubing.

There are plenty of these charts online, and all you have to do if find one that suits your conversion or matching needs. An example of a brass fittings size chart that you could use is seen above. That being said, it’s also important that you understand what your measurements mean as explained below:

  • Always remember that nominal measurements will vary slightly across different pipes since the value depends on the pipe thickness.
  • On the other hand, outside brass pipe fitting dimensions remain the same. That’s because varying pipe thickness only changes the ID or inner diameter.
  • So you’ll normally find your fitting size dependent on the pipe OD. That’s because the fitting goes over the pipe, the diameter of which remains constant.


Knowing how to measure brass fittings the right way can mean the different between achieving a proper fit, or mismatching the two and ending up with a weak connection. So, whether looking to match pipe and brass fitting sizes for plumbing and gas applications or other need, be sure to use the right measurements.

Contact US

Contact Us