Thread inch dimensions of the plumbing and heating industry

The following table serves as information for customers who are not in the heating or plumbing industry. It is often assumed that 1" is the equivalent of 25.4 mm. Although this is correct, it does not mean that a 1/2" pipe has half the diameter, i.e. 12.7 mm.!

Since the inside diameter of pipes is the value that matters, at the beginning of the 20th century a 1" pipe still had a clear width of 25.4 mm. With the steel quality of the time, this resulted in an outside diameter of approx. 33 mm. As steel quality improved in later times, the pipe walls also became thinner and thinner. However, the fittings and threading tools were manufactured according to the outside diameter, so the inside diameters became larger. In the heating and plumbing industry, inch values no longer correspond to any of today's measurements. Pipe dimensions in "inches" are defined metrically nowadays. Among other things, this is also defined in the DIN EN ISO 228-1 standard, although the internal diameter of the pipe is not described in the standard. If you now have a pipe with an outside diameter of about 33 mm, then it is and remains a "1 inch pipe"!

Inch/Zoll	Outside ø in mm	Inside ø in mm
1/8"	9.51 - 9.73	ca. 8.5
1/4"	12.91 - 13.12	ca. 11.5
3/8"	16.41 - 16.66	ca. 15.0
1/2"	20.67 - 20.96	ca. 18.5
3/4"	26.16 - 26.44	ca. 24.0
1"	32.89 - 33.25	ca. 30.0
1 1/4"	41.55 - 41.91	ca. 39.0
1 1/2"	47.44 - 47.80	ca. 45.0
2"	59.25 - 59.61	ca. 57.0

We hope that this information will provide you with a small overview when selecting articles that refer to customs dimensions and that you will thus avoid incorrect orders.

Your Proflamm Service Team