American Watch Movement Sizes:
| Size | Inches | Millimeters | Lignes |
|---|---|---|---|
| 20S | 1 5/6 | 46.56 | 20.62 |
| 18S | 1 23/30 | 44.86 | 19.87 |
| 17S | 1 11/15 | 44.02 | 19.50 |
| 16S | 1 7/10 | 43.18 | 19.12 |
| 14S | 1 19/30 | 41.48 | 18.37 |
| 12S | 1 17/30 | 39.78 | 17.62 |
| 10S | 1 1/2 | 38.10 | 16.87 |
| 8S | 1 13/30 | 36.40 | 16.12 |
| 6S | 1 11/30 | 34.70 | 15.37 |
| 0S | 1 1/6 | 29.62 | 13.12 |
| 3/0 | 1 1/10 | 27.94 | 12.37 |
| 6/0 | 1 | 25.40 | 11.25 |
| 8/0 | 14/15 | 23.71 | 10.5 |
| 10/0 | 26/30 | 22.01 | 9.75 |
| 16/0 | 2/3 | 16.93 | 7.5 |
Lancashire Gauge is the standard commonly used by American watch manufacturers. Every 1/30 of an inch added increased the size one number. Watch movement is measured at the dial plate. Railroad standard pocket watches were either 18-size or 16-size. 18-size watches dominated during the nineteenth century, 16-size watch movement production exceeded 18-size watches by 1915.
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