Free tool · Pipe threads
Pipe thread chart: G, R and Rp in mm.
A 1/2 inch pipe thread is 20.955 mm across, not 12.7 mm. Look up the Whitworth pipe threads to ISO 228-1 and ISO 7-1 from 1/16 to 6 inch: major, pitch and minor diameter, threads per inch and the pipe each thread sits on.
What does the line say?
Paste an order or tender line. The tool reads the nominal size, inch size, dimensions, material and length and looks up the standard.
socket G 1/2 female
- Pipe system
- Threaded steel pipe, EN 10255
- Item
- Socket
- Material
- Steel
- Nominal size
- DN 15
- Inch
- 1/2"
- OD × wall
- 21.3 × 2.6 mm (Series M)
- Inside diameter
- 16.1 mm
- Volume
- 0.204 l/m
- Thread
- G 1/2" · G (ISO 228-1, parallel), female
- Thread Ø
- 20.955 mm
- TPI
- 14
- Pitch
- 1.814 mm
- Minor Ø
- 18.631 mm
- A 1/2" thread sits on threaded pipe DN 15 (21.3 mm outside).
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Inch pipe threads in mm
- Thread Ø
- 20.955 mm
- TPI
- 14
- Pitch
- 1.814 mm
- Minor Ø
- 18.631 mm
- Pitch Ø
- 19.793 mm
- Gauge length (ISO 7-1)
- 8.2 mm
Fits threaded pipe DN 15: 21.3 mm outside diameter.
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Pipe dimensions by standard
All sizes in mm. Inside diameter, volume and weight are calculated from outside diameter and wall. No liability; the standard and the manufacturer's data sheet apply.
Pipe thread chart (Whitworth): G, R and Rp
Pipe threads to ISO 228-1 (G, parallel, not sealing on the thread) and ISO 7-1 (R taper external, Rp parallel internal, sealing on the thread). Both use the Whitworth form (55°) and the same diameters. Gauge length for ISO 7-1 only.
| Size | Thread Ø | TPI | Pitch | Pitch Ø | Minor Ø | Gauge length R | DN |
|---|---|---|---|---|---|---|---|
| G / R 1/16" | 7.723 | 28 | 0.907 | 7.142 | 6.561 | 4.0 | – |
| G / R 1/8" | 9.728 | 28 | 0.907 | 9.147 | 8.566 | 4.0 | DN 6 |
| G / R 1/4" | 13.157 | 19 | 1.337 | 12.301 | 11.445 | 6.0 | DN 8 |
| G / R 3/8" | 16.662 | 19 | 1.337 | 15.806 | 14.950 | 6.4 | DN 10 |
| G / R 1/2" | 20.955 | 14 | 1.814 | 19.793 | 18.631 | 8.2 | DN 15 |
| G / R 5/8" | 22.911 | 14 | 1.814 | 21.749 | 20.587 | – | – |
| G / R 3/4" | 26.441 | 14 | 1.814 | 25.279 | 24.117 | 9.5 | DN 20 |
| G / R 7/8" | 30.201 | 14 | 1.814 | 29.039 | 27.877 | – | – |
| G / R 1" | 33.249 | 11 | 2.309 | 31.770 | 30.291 | 10.4 | DN 25 |
| G / R 1 1/8" | 37.897 | 11 | 2.309 | 36.418 | 34.939 | – | – |
| G / R 1 1/4" | 41.910 | 11 | 2.309 | 40.431 | 38.952 | 12.7 | DN 32 |
| G / R 1 1/2" | 47.803 | 11 | 2.309 | 46.324 | 44.845 | 12.7 | DN 40 |
| G / R 1 3/4" | 53.746 | 11 | 2.309 | 52.267 | 50.788 | – | – |
| G / R 2" | 59.614 | 11 | 2.309 | 58.135 | 56.656 | 15.9 | DN 50 |
| G / R 2 1/4" | 65.710 | 11 | 2.309 | 64.231 | 62.752 | – | – |
| G / R 2 1/2" | 75.184 | 11 | 2.309 | 73.705 | 72.226 | 17.5 | DN 65 |
| G / R 2 3/4" | 81.534 | 11 | 2.309 | 80.055 | 78.576 | – | – |
| G / R 3" | 87.884 | 11 | 2.309 | 86.405 | 84.926 | 20.6 | DN 80 |
| G / R 3 1/2" | 100.330 | 11 | 2.309 | 98.851 | 97.372 | – | – |
| G / R 4" | 113.030 | 11 | 2.309 | 111.551 | 110.072 | 25.4 | DN 100 |
| G / R 4 1/2" | 125.730 | 11 | 2.309 | 124.251 | 122.772 | – | – |
| G / R 5" | 138.430 | 11 | 2.309 | 136.951 | 135.472 | 28.6 | DN 125 |
| G / R 5 1/2" | 151.130 | 11 | 2.309 | 149.651 | 148.172 | – | – |
| G / R 6" | 163.830 | 11 | 2.309 | 162.351 | 160.872 | 28.6 | DN 150 |
Standard: ISO 228-1:2000, ISO 7-1:1994 (DIN EN 10226-1)
Pipe inch sizes in DN and mm
Threaded steel pipe to EN 10255 (formerly DIN 2440/2441): inch size, DN, outside diameter and wall of series M (medium) and H (heavy), with the thread diameter to ISO 228-1/ISO 7-1.
| Inch | DN | OD | Wall M | Wall H | ID M | Thread Ø | TPI | Inch as length |
|---|---|---|---|---|---|---|---|---|
| 1/8" | DN 6 | 10.2 | 2.0 | – | 6.2 | 9.728 | 28 | 3.175 |
| 1/4" | DN 8 | 13.5 | 2.3 | – | 8.9 | 13.157 | 19 | 6.35 |
| 3/8" | DN 10 | 17.2 | 2.3 | 2.9 | 12.6 | 16.662 | 19 | 9.525 |
| 1/2" | DN 15 | 21.3 | 2.6 | 3.2 | 16.1 | 20.955 | 14 | 12.7 |
| 3/4" | DN 20 | 26.9 | 2.6 | 3.2 | 21.7 | 26.441 | 14 | 19.05 |
| 1" | DN 25 | 33.7 | 3.2 | 4.0 | 27.3 | 33.249 | 11 | 25.4 |
| 1 1/4" | DN 32 | 42.4 | 3.2 | 4.0 | 36.0 | 41.910 | 11 | 31.75 |
| 1 1/2" | DN 40 | 48.3 | 3.2 | 4.0 | 41.9 | 47.803 | 11 | 38.1 |
| 2" | DN 50 | 60.3 | 3.6 | 4.5 | 53.1 | 59.614 | 11 | 50.8 |
| 2 1/2" | DN 65 | 76.1 | 3.6 | 4.5 | 68.9 | 75.184 | 11 | 63.5 |
| 3" | DN 80 | 88.9 | 4.0 | 5.0 | 80.9 | 87.884 | 11 | 76.2 |
| 4" | DN 100 | 114.3 | 4.5 | 5.4 | 105.3 | 113.030 | 11 | 101.6 |
| 5" | DN 125 | 139.7 | 5.0 | 5.4 | 129.7 | 138.430 | 11 | 127.0 |
| 6" | DN 150 | 165.1 | 5.0 | 5.4 | 155.1 | 163.830 | 11 | 152.4 |
Pipe sizes, DN chart and calculator
Standard: EN 10255:2004+A1:2007, ISO 228-1:2000
Why this chart
Built for the threads orders arrive in.
01
1/2 inch is 20.955 mm
The inch size names the pipe, not the thread. A 1/2 inch thread is 20.955 mm across and sits on a pipe that is 21.3 mm outside.
02
G, R and Rp side by side
Parallel G threads to ISO 228-1 and sealing R and Rp threads to ISO 7-1 in one table, with the ISO 7-1 gauge length and the matching EN 10255 pipe.
03
Every value checked twice
Each dimension follows the standard named on its table and matches at least two independent public sources, such as maker data sheets and stockist tables.
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FAQ
Questions about pipe threads.
G is a parallel pipe thread to ISO 228-1 (Whitworth form, 55°) and 1/2 the nominal size. G 1/2 has a 20.955 mm major diameter and 14 threads per inch (1.814 mm pitch). It does not seal on the thread but with a washer or O-ring.
G (ISO 228-1) is parallel and does not seal on the thread. R is a taper external thread and Rp a parallel internal thread to ISO 7-1 (formerly DIN 2999); R and Rp seal on the thread, for example with hemp or tape. All three share the same diameters and pitches.
The inch size names the pipe, not the thread diameter. The thread is cut on the outside of the pipe: a 1/2 inch pipe is 21.3 mm outside, and its thread 20.955 mm.
Measure the outside diameter of a male thread and count the threads over 25.4 mm (one inch). About 21 mm and 14 threads is 1/2", 26.4 mm and 14 threads is 3/4", 33.2 mm and 11 threads is 1".
No. BSP (Whitworth, 55°) is the pipe thread used in Europe, standardised as ISO 228-1 (BSPP, G) and ISO 7-1 (BSPT, R/Rp). NPT is the American pipe thread with a 60° angle; most sizes have different pitches, so the two do not fit together.
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