Inches to mm — converter and DN / BSP reference table
This inches to mm converter allows you to quickly convert inches to millimeters or millimeters to inches. You will also find a DN ↔ inch ↔ mm reference table — ideal for selecting pipes, threads, and fittings according to standard DN (nominal diameter).
? Inches ↔ mm converter
DN ↔ Inch ↔ mm reference table
| DN | Inch (BSP) | Outer Ø mm | Inner Ø mm (approx.) |
|---|---|---|---|
| DN 6 | 1/8" | 10,2 | 6,8 |
| DN 8 | 1/4" | 13,5 | 9,2 |
| DN 10 | 3/8" | 17,2 | 12,5 |
| DN 15 | 1/2" | 21,3 | 15,8 |
| DN 20 | 3/4" | 26,9 | 20,4 |
| DN 25 | 1" | 33,7 | 26,6 |
| DN 32 | 1 1/4" | 42,4 | 35,2 |
| DN 40 | 1 1/2" | 48,3 | 41,0 |
| DN 50 | 2" | 60,3 | 52,5 |
| DN 65 | 2 1/2" | 76,1 | 68,0 |
| DN 80 | 3" | 88,9 | 80,9 |
| DN 100 | 4" | 114,3 | 105,3 |
Inch to millimeter ratio
One inch (1") equals exactly 25.4 mm. This value is an international standard (ISO 31-1). Conversion formulas:
- Inches → mm: mm = inches × 25.4
- mm → inches: inches = mm ÷ 25.4
DN system for pipes
DN (Diameter Nominal) — nominal pipe diameter according to EN ISO 6708. Important: DN does not correspond to the actual outer diameter — it is a conditional value used to select fittings, valves, and pump connections.
Frequently asked questions
What is a 1/2 inch pipe in millimeters?
The outer diameter of a 1/2" (DN 15) pipe according to EN standard is 21.3 mmThis is the most commonly used diameter in plumbing and heating systems.
What is the difference between BSP/G and NPT threads?
BSP (British Standard Pipe) / G threads are used in Europe and Asia, while NPT (National Pipe Taper) is used in the USA and Canada. They are not compatible with each other, so it is important to correctly identify the thread type.
How to convert 3/4 inch to mm?
3/4" = 0.75 × 25.4 = 19.05 mmThe outer diameter of a DN 20 pipe (equivalent to 3/4") is 26.9 mm.
Does Karuselė sell pipes according to DN?
Yes — our stainless steel pipes range is described by outer diameter and wall thickness corresponding to nominal DN.