# Watch Movement Size Measuring Systems [9/6/00]

From The Workbench October 1, 2002 admin

# Watch Movement Measuring Systems

The following information on watch sizes and the conversion tables is taken directly from the 1957 Watch Material Distributors Association of America Catalog (just laboriously re-typed into html format!). This is the most comprehensive set of tables and information I have seen on the subject. Although there are watch size gauges available from material suppliers, they don’t give exact numerical values and equivalents if you require precise conversion values. Hopefully this information will answer all of your watch size questions.

### WATCH SIZES

A watch movement’s size is gauged by measuring it across its center on the dial side through its narrowest point. This system is used by the U.S. Customs in determining the amount dutiable on imported movements, and thus it has become associated with the sizing of all watch movements brought into this country. Although the use of the millimeter to determine watch sizes is growing steadily, the predominant system still in use is the LIGNE. The LIGNE is equal to the twelfth part of the French Inch, which is approximately 1/16th larger than our own inch. One French ligne=2.25583 or roughly 2¼ mm. Thus a 10 ligne movement should gauge 22.5mm. In inches this would measure .8881 as the LIGNE is equal to .0888 parts of an inch. (Note: These days, movement sizes are more commonly stated in millimeters – Rob B)

The SIZE as a gauge with which to measure movements is still used by some of the older American watch manufacturers to indicate the dimensions of their movements. The SIZE as a unit has its basis in the old “0” size movement. This movement measures 1 5/30″. A difference of 1/30″ accounts for each size smaller or larger than the starting point of the system, the “0” size watch movement. Thus a “1” size movement would be 1 6/30″, a “6” size movement 1 11/30″. Watch movements smaller than the “0” size are designated by adding zeros to the size. Thus a movement one size smaller than the “0” would be a 2/0 size movement and would gauge 1 4/30″, the 3/0 size would then measure 1 3/30. Conversely, the “25” size watch movement would measure just 2 full inches.

A good way to remember sizes of the American and Swiss gauges is to associate the unit we know best, the inch, with both the American and Swiss equivalents. For example, the 6/0 size American movement is exactly one inch in diameter (“0″ size = 1 5/30″ – 5/30″ = one inch). Also, the Swiss 11¼ Ligne is just a few ten thousandths of an inch under one inch, and can be called a one-inch watch movement.

The following tables should make it easy to determine movement size equivalents.

 Lignes Size Millimeters Inches Lignes Size Millimeters Inches ¼ 35/0 0.05640 0.0222 10½ 8/0 23.686 0.9325 ½ – 1.128 0.0444 10¾ – 24.250 0.9547 ¾ 34/0 1.692 0.0666 11 7/0 24.814 0.9770 1 – 2.255 0.0888 11¼ 6/0 25.387 0.9992 1¼ 33/0 2.820 0.1111 11½ – 25.942 1.0214 1½ 32/0 3.338 0.1332 11¾ 5/0 26.506 1.0436 1¾ 31/0 3.949 0.1554 12 4/0 27.070 1.0658 2 – 4.517 .01776 12½ 3/0 28.198 1.1102 2¼ 30/0 5.076 0.1998 12¾ 2/0 28.762 1.1324 2½ – 5.640 0.2220 13 0 29.326 1.1546 2¾ 29/0 6.204 0.2442 13½ 1 30.453 1.1990 3 28/0 6.786 0.2664 14 2 31.581 1.2434 3¼ 27/0 7.332 0.2886 14¼ 3 32.046 1.2656 3½ – 7.895 0.3108 14¾ 4 33.273 1.3100 3¾ 26/0 8.459 0.3330 15 5 33.838 1.3322 4 – 9.023 0.3553 15½ 6 34.955 1.3766 4¼ 25/0 9.587 0.3775 15¾ 7 35.529 1.3988 4½ 24/0 10.151 0.3997 16 – 36.093 1.4210 4¾ – 10.715 0.4219 16¼ 8 36.657 1.4432 5 23/0 11.279 0.4441 16½ 9 37.221 1.4654 5¼ 22/0 11.843 0.4663 17 10 38.349 1.5098 5½ – 12.407 0.4885 17¼ 11 38.913 1.5320 5¾ 21/0 12.971 0.5107 17¾ 12 40.041 1.5764 6 20/0 13.535 0.5329 18 13 40.605 1.5987 6¼ – 14.099 0.5513 18½ 14 41.733 1.6431 6½ 19/0 14.663 0.5773 18¾ 15 42.297 1.6653 6¾ 18/0 15.227 0.5995 19 – 42.861 1.6875 7 – 15.791 0.6217 19¼ 16 43.425 1.7097 7¼ 17/0 16.355 0.6439 19½ 17 43.989 1.7319 7½ 16/0 16.919 0.6661 20 18 45.117 1.7763 7¾ – 17.483 0.6883 21 21 47.372 1.8651 8 15/0 18.047 0.7105 22 23 49.628 1.9539 8¼ 14/0 18.611 0.7327 23 26 51.884 2.0427 8½ – 19.175 0.7549 24 29 54.140 2.1315 8¾ 13/0 19.739 0.7771 25 32 56.396 2.2204 9 12/0 20.303 0.7993 26 34 58.652 2.3092 9¼ – 20.867 0.8215 27 37 60.907 2.3980 9½ 11/0 21.430 0.8437 28 40 63.163 2.4868 9¾ 10/0 21.994 0.8659 29 43 65.419 2.5756 10 9/0 22.558 0.8881 30 45 67.675 2.6644 10¼ – 23.122 09103