Inch fractions in mm
| Inch fraction | Inches (decimal) | mm |
|---|---|---|
| 1/16″ | 0.0625 | 1.59 |
| 1/8″ | 0.1250 | 3.18 |
| 3/16″ | 0.1875 | 4.76 |
| 1/4″ | 0.2500 | 6.35 |
| 5/16″ | 0.3125 | 7.94 |
| 3/8″ | 0.3750 | 9.52 |
| 7/16″ | 0.4375 | 11.11 |
| 1/2″ | 0.5000 | 12.70 |
| 9/16″ | 0.5625 | 14.29 |
| 5/8″ | 0.6250 | 15.88 |
| 11/16″ | 0.6875 | 17.46 |
| 3/4″ | 0.7500 | 19.05 |
| 13/16″ | 0.8125 | 20.64 |
| 7/8″ | 0.8750 | 22.22 |
| 15/16″ | 0.9375 | 23.81 |
| 1″ | 1.0000 | 25.40 |
Whole and mixed inches in mm
| Inches | Inches (decimal) | mm |
|---|---|---|
| 1 1/4″ | 1.25 | 31.75 |
| 1 1/2″ | 1.50 | 38.10 |
| 1 3/4″ | 1.75 | 44.45 |
| 2″ | 2.00 | 50.80 |
| 2 1/2″ | 2.50 | 63.50 |
| 3″ | 3.00 | 76.20 |
| 4″ | 4.00 | 101.60 |
| 5″ | 5.00 | 127.00 |
| 6″ | 6.00 | 152.40 |
| 8″ | 8.00 | 203.20 |
| 10″ | 10.00 | 254.00 |
| 12″ | 12.00 | 304.80 |
DN, inches and the outside diameter of pipes
DN (nominal diameter) is a reference number, not an exact size. For plumbing pipes, “1 inch” was originally the inside diameter; that is why a 1″ pipe (DN 25) has an outside diameter of 33.7 mm.
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| DN | Inch (name) | Outside Ø (mm) |
|---|---|---|
| DN 6 | ⅛″ | 10.2 |
| DN 8 | ¼″ | 13.5 |
| DN 10 | ⅜″ | 17.2 |
| DN 15 | ½″ | 21.3 |
| DN 20 | ¾″ | 26.9 |
| DN 25 | 1″ | 33.7 |
| DN 32 | 1¼″ | 42.4 |
| DN 40 | 1½″ | 48.3 |
| DN 50 | 2″ | 60.3 |
| DN 65 | 2½″ | 76.1 |
| DN 80 | 3″ | 88.9 |
| DN 100 | 4″ | 114.3 |
| DN 125 | 5″ | 139.7 |
| DN 150 | 6″ | 168.3 |
| DN 200 | 8″ | 219.1 |
| DN 250 | 10″ | 273.0 |
| DN 300 | 12″ | 323.9 |
| DN 350 | 14″ | 355.6 |
| DN 400 | 16″ | 406.4 |
| DN 450 | 18″ | 457.0 |
| DN 500 | 20″ | 508.0 |
The outside diameters are those of the usual series in EN 10220 / ISO 4200. The wall thickness is chosen separately, depending on pressure and on the pipe standard.
Frequently asked questions
How many mm is 1 inch?
Exactly 25.4 mm. 1/2″ = 12.7 mm, 3/4″ = 19.05 mm, 1 1/4″ = 31.75 mm.
What does DN mean for a pipe?
DN is the nominal diameter: a reference number that ties the sizes together (DN 25 corresponds to the 1″ name). It is neither the exact outside nor inside diameter.
Why is a 1″ pipe 33.7 mm and not 25.4 mm?
For pipes, the inch name comes from the old inside diameter, not the outside one. The standard outside diameter of a 1″ pipe is 33.7 mm.
How much does a round pipe of a given diameter weigh?
It depends on the wall thickness. Choose the diameter and thickness in the round tube weight calculator.