Pipe & tube diameter converter
Fractional inches ⇄ millimetres, with size identification
Fractional inches → mm
+
/
mm → fractional inches
Precision
Unit
I measured the…
Type what your caliper reads. Matching standard sizes appear below.
Showing sizes within ±2% (min ±1.6 mm).
Reference tables (no script needed)
Common fractions ⇄ mm
| 1/16″ | 1.588 | 9/16″ | 14.288 |
| 1/8″ | 3.175 | 5/8″ | 15.875 |
| 3/16″ | 4.763 | 11/16″ | 17.463 |
| 1/4″ | 6.350 | 3/4″ | 19.050 |
| 5/16″ | 7.938 | 13/16″ | 20.638 |
| 3/8″ | 9.525 | 7/8″ | 22.225 |
| 7/16″ | 11.113 | 15/16″ | 23.813 |
| 1/2″ | 12.700 | 1″ | 25.400 |
Steel pipe sizes — ASME B36.10 (mm)
| NPS | DN | OD | ID Sch 40 | ID Sch 80 |
|---|---|---|---|---|
| 1/8 | 6 | 10.29 | 6.83 | 5.46 |
| 1/4 | 8 | 13.72 | 9.25 | 7.67 |
| 3/8 | 10 | 17.15 | 12.52 | 10.74 |
| 1/2 | 15 | 21.34 | 15.80 | 13.87 |
| 3/4 | 20 | 26.67 | 20.93 | 18.85 |
| 1 | 25 | 33.40 | 26.64 | 24.31 |
| 1-1/4 | 32 | 42.16 | 35.05 | 32.46 |
| 1-1/2 | 40 | 48.26 | 40.89 | 38.10 |
| 2 | 50 | 60.33 | 52.50 | 49.25 |
| 2-1/2 | 65 | 73.03 | 62.71 | 59.00 |
| 3 | 80 | 88.90 | 77.93 | 73.66 |
| 3-1/2 | 90 | 101.60 | 90.12 | 85.45 |
| 4 | 100 | 114.30 | 102.26 | 97.18 |
| 5 | 125 | 141.30 | 128.19 | 122.25 |
| 6 | 150 | 168.28 | 154.05 | 146.33 |
| 8 | 200 | 219.08 | 202.72 | 193.68 |
| 10 | 250 | 273.05 | 254.51 | 242.87 |
| 12 | 300 | 323.85 | 303.23 | 288.90 |
EN 10220 outside diameters differ at some sizes (DN25 33.7 · DN32 42.4 · DN65 76.1 · DN125 139.7). Copper tube per ASTM B88: OD = nominal + 1/8″.