Australian Standard Measurement and Sizing Chart

Size	Male Fitting End	Male / Female Fitting (OD)	Threads Per Inch	Actual Barb End
6	⅛″	10	28	3
7	3⁄16″			4
8	¼″	13	19	6
9	5⁄16″			8
10	⅜″	17	19	10
15	½″	21	14	13
18	⅝″			16
20	¾″	26	14	19
25	1″	33	11	25
32	1¼″	42	11	32
40	1½″	48	11	38
50	2″	60	11	51
65	2½″	75	11	64
80	3″	88	11	76
100	4″	114	11	101
150	6″	165	11	152

How to Measure BSP Thread Accurately in Australia

If you are installing valves, fittings or pipework in Australia, knowing how to measure BSP thread accurately is essential. Choosing the wrong thread size leads to leaks, damaged fittings and wasted time on site.

As a plumbing specialist working with Valve Warehouse Australia, I regularly see issues caused by incorrect BSP measurements. The process is simple once you understand that BSP sizing is based on trade size, not the physical diameter you measure.

Watch the supporting video above where I demonstrate the full process step by step.

What Is BSP Thread

BSP stands for British Standard Pipe. It is the most common pipe thread type used in Australian plumbing, irrigation and hydraulic systems.

There are two main types:

BSPP which is parallel thread
BSPT which is tapered thread

Correct identification is the first step before measuring.

How to Measure BSP Thread Accurately

To measure BSP thread accurately, you must measure the thread diameter correctly, confirm the thread pitch, and then match your results to a BSP thread chart.

Step 1 — Identify Parallel or Tapered

Parallel BSPP threads have a consistent diameter along the entire thread.

Tapered BSPT threads gradually reduce in diameter toward the end.

For tapered threads, measure the diameter at the fourth or fifth full thread from the end. This provides a more accurate reference point due to taper and manufacturing tolerances.

Step 2 — Measure the Diameter Correctly

For a male BSP fitting:
Use vernier callipers to measure the outside diameter across the threads.

For a female BSP fitting:
Measure the internal diameter from inside wall to inside wall.

Important: BSP sizes do not match the physical measurement in millimetres. For example, a 1/2 inch BSP male thread measures approximately 20.9 mm across the outside. Like the watermarked brass hex nipple male x male.

Why Does a 1/2 Inch BSP Measure About 21 mm?

BSP thread sizes are based on nominal pipe bore, not the outside diameter of the thread. The nominal bore refers to the approximate internal diameter of the original pipe standard.

This means a 1/2 inch BSP thread will measure around 21 mm across the outside, even though it is labelled 1/2 inch.

You must always measure and then reference a BSP thread chart to determine the correct trade size.

Step 3 — Confirm Threads Per Inch

Use a thread pitch gauge to measure threads per inch.

For example:

1/2 inch BSP has 14 threads per inch
3/4 inch BSP has 14 threads per inch
1 inch BSP has 11 threads per inch

Confirming both diameter and pitch ensures accurate identification.

Step 4 — Match to a BSP Thread Chart

Once you know:

Whether the thread is parallel or tapered
The measured diameter
The threads per inch

You must match these measurements against a BSP reference table to determine the correct trade size. Never assume the measured diameter equals the labelled size.

Common Problems When Measuring BSP Thread

Using a tape measure instead of calipers
Assuming thread size equals measured diameter
Confusing BSP with NPT thread
Not measuring tapered threads at the correct point
Ignoring thread pitch

These mistakes lead to cross threading and leaks.

Choosing the Right BSP Valves and Fittings

Once you have measured your BSP thread accurately, selecting compatible valves becomes straightforward.

Explore our range of:

Brass BSP ball valves Stainless Steel BSP valves BSP threaded check valves BSP pressure reducing valves

All available at Valve Warehouse Australia with clearly listed thread specifications.

If you are unsure which valve matches your thread type, contact our team for guidance before purchasing.

Frequently Asked Questions About Measuring BSP Thread

How do I measure BSP thread size accurately?

To measure BSP thread size accurately, first identify whether the thread is parallel or tapered. Measure the outside diameter of a male thread or the inside diameter of a female thread using vernier callipers. Then measure the threads per inch with a thread pitch gauge. Finally, match your measurements to a BSP thread chart to determine the correct trade size.

Why does BSP thread size not match the measured diameter?

BSP thread sizes are based on nominal pipe bore rather than the physical outside diameter of the thread. For example, a 1/2 inch BSP thread measures about 20.9 mm across the outside. The labelled size refers to the original pipe standard, not the measured thread width.

How can I tell if a BSP thread is tapered or parallel?

A parallel BSPP thread maintains the same diameter along the entire thread length. A tapered BSPT thread gradually reduces in diameter toward the end. You can confirm this by measuring the diameter at different points along the thread. If the measurement changes, it is tapered.

What tool do I need to measure BSP thread?

The correct tools are vernier callipers to measure diameter and a thread pitch gauge to measure threads per inch. Using a ruler or tape measure is better than nothing but not ideal for accurately identifying BSP thread sizes.

What happens if I use the wrong BSP thread size?

Using the wrong BSP thread size can cause cross threading, leaks and damage to valves or fittings. It can also lead to costly replacements and downtime on site. Always confirm diameter, thread pitch and thread type before installing any valve or fitting.