When choosing stainless steel metal products, buyers often encounter two different measurement systems. In drawings or technical specifications, sizes may be specified in inches (e.g., 1" or 2" pipe), while real warehouse inventory and tools (calipers) operate in millimeters.
Stainless Steel Pipes: How to Avoid Sizing Mistakes? Millimeter to Inch Conversion Table
Pipe Size Correspondence Table UKIRS DATA SHEET | ||||
|---|---|---|---|---|
| Outer ∅ (mm) | Outer ∅ (inch ≈) | Wall (mm) | Inner ∅ (mm) | Inner ∅ (inch ≈) |
| 6 | 1/4" | 1.0 | 4.0 | 5/32" |
| 8 | 5/16" | 1.0 | 6.0 | 1/4" |
| 10 | 3/8" | 0.8; 1.0; 1.5 | 8.4; 8.0; 7.0 | 21/64"; 5/16"; 9/32" |
| 12 | 15/32" | 1.0; 1.2; 1.5; 2.0 | 10.0; 9.6; 9.0; 8.0 | 25/64"; 3/8"; 23/64"; 5/16" |
| 14 | 9/16" | 1.0; 1.5; 2.0 | 12.0; 11.0; 10.0 | 15/32"; 7/16"; 3/8" |
| 15 | 19/32" | 1.5 | 12.0 | 15/32" |
| 16 | 5/8" | 1.0; 1.2; 1.5; 2.0 | 14.0; 13.6; 13.0; 12.0 | 35/64"; 17/32"; 1/2"; 15/32" |
| 18 | 11/16" | 1.0; 1.5 | 16.0; 15.0 | 5/8"; 19/32" |
| 19 | 3/4" | 1.5 | 16.0 | 5/8" |
| 20 | 25/32" | 1.0; 1.2; 1.5; 2.0 | 18.0; 17.6; 17.0; 16.0 | 45/64"; 11/16"; 21/32"; 5/8" |
| 21.3 | 27/32" | 3.0 | 15.3 | 19/32" |
| 22 | 7/8" | 1.5 | 19.0 | 3/4" |
| 25 | 1" (63/64") | 1.0; 1.2; 1.5; 2.0; 3.0 | 23.0; 22.6; 22.0; 21.0; 19.0 | 29/32"; 57/64"; 7/8"; 13/16"; 3/4" |
| 26.9 | 1 1/16" | 3.0 | 20.9 | 13/16" |
| 28 | 1 3/32" | 1.5 | 25.0 | 63/64" |
| 30 | 1 3/16" | 1.5; 2.0 | 27.0; 26.0 | 1 1/16"; 1 1/32" |
| 32 | 1 1/4" | 1.2; 1.5; 2.0; 2.5; 3.0 | 29.6; 29.0; 28.0; 27.0; 26.0 | 1 5/32"; 1 9/64"; 1 7/64"; 1 1/16"; 1 1/32" |
| 33.7 | 1 11/32" | 1.5 | 30.7 | 1 7/32" |
| 38 | 1 1/2" | 1.2; 1.5; 2.0 | 35.6; 35.0; 34.0 | 1 13/32"; 1 3/8"; 1 11/32" |
| 40 | 1 37/64" | 1.0; 1.5; 2.0 | 38.0; 37.0; 36.0 | 1 1/2"; 1 15/32"; 1 13/32" |
| 42.4 | 1 21/32" | 1.2; 1.5; 2.0; 3.0 | 40.0; 39.4; 38.4; 36.4 | 1 37/64"; 1 9/16"; 1 33/64"; 1 7/16" |
| 45 | 1 25/32" | 1.5 | 42.0 | 1 21/32" |
| 48.3 | 1 29/32" | 1.5; 3.0 | 45.3; 42.3 | 1 25/32"; 1 21/32" |
| 50.8 | 2" | 1.2; 1.5; 2.0 | 48.4; 47.8; 46.8 | 1 29/32"; 1 7/8"; 1 27/32" |
| 52 | 2 3/64" | 1.5 | 49.0 | 1 15/16" |
| 54 | 2 1/8" | 1.5 | 51.0 | 2" |
| 57 | 2 1/4" | 1.5; 2.0; 3.0 | 54.0; 53.0; 51.0 | 2 1/8"; 2 3/32"; 2" |
| 60.3 | 2 3/8" | 1.5; 2.0; 3.0 | 57.3; 56.3; 54.3 | 2 1/4"; 2 7/32"; 2 1/8" |
| 70 | 2 3/4" | 1.5; 2.0 | 67.0; 66.0 | 2 5/8"; 2 19/32" |
| 76.1 | 3" | 1.5; 2.0 | 73.1; 72.1 | 2 7/8"; 2 27/32" |
| 80 | 3 5/32" | 1.5; 2.0 | 77.0; 76.0 | 3 1/32"; 3" |
| 84 | 3 5/16" | 1.5 | 81.0 | 3 3/16" |
| 85 | 3 11/32" | 2.0 | 81.0 | 3 3/16" |
| 88.9 | 3 1/2" | 1.5; 2.0 | 85.9; 84.9 | 3 3/8"; 3 11/32" |
| 101.6 | 4" | 1.5; 2.0 | 98.6; 97.6 | 3 7/8"; 3 27/32" |
| 108 | 4 1/4" | 2.0 | 104.0 | 4 3/32" |
| 114.3 | 4 1/2" | 2.0 | 110.3 | 4 11/32" |
| 129 | 5 5/64" | 2.0 | 125.0 | 4 59/64" |
* Calculated inch values are provided for reference. Inner diameter is calculated using the formula: d = D - (2 × S).
Why does confusion arise?
In the stainless steel industry, various standards exist (DIN, ISO, SMS), where the same "inch" can represent a different actual diameter. For example, a 1" pipe can be 25.0 mm, 25.4 mm, or even 33.7 mm if it refers to a water pipe standard.
To simplify the selection process for you, we have prepared a comprehensive correspondence table for the entire range of round stainless steel pipes from Ukirs.
In this table, you will find:
- Exact outer diameter in millimeters.
- The closest commonly accepted inch equivalent.
- Internal passage calculation based on wall thickness.
Use this data for the precise selection of fasteners, caps, fittings, and other hardware for stainless steel structures.