Watch Movement Measuring Systems

# Watch Movement Measuring Systems

THE ORIGINS OF WATCH SIZE MEASUREMENTS

Although the use of the millimeter to determine watch sizes is commonplace now, the predominant system still in use up until the 1960's and even to some extent in the 1970's, was 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=2.25583mm or roughly 2¼ mm. Thus a 10 ligne movement should measure 22.5mm. In inches this would be 0.8881 as the LIGNE is equal to .0888 parts of an inch.

American watch manufacturers used to indicate the dimensions of their movements, by means of their own unique "Size" gauge. The "SIZE", as a unit of measurement, had its basis in their old "0" size movement. This movement measures 1" + 5/30" in diameter. Each difference in diameter of 1/30" accounts for each size smaller or larger than the starting point of the system, ie. the "0" size watch movement. Thus a "1" size movement would be 1" + 5/30" +1/30", or 1"+ 6/30" (or 1.2") and a "6" size movement would be 1 + 5/30 + 6/30", or 1 + 11/30" (or 1.366"). 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 measure 1" + 5/30" - 1/30", the 3/0 size would then measure 1" +5/30" - 3/30". Conversely, the "25" size watch movement would measure just 2 full inches. A very confusing system compared to the modern simple metric system!

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

Lignes Size Millimeters Inches
¼ 35/0 0.05640 0.0222
½ - 1.128 0.0444
¾ 34/0 1.692 0.0666
1 - 2.255 0.0888
33/0 2.820 0.1111
32/0 3.338 0.1332
31/0 3.949 0.1554
2 - 4.517 0.1776
30/0 5.076 0.1998
- 5.640 0.2220
29/0 6.204 0.2442
3 28/0 6.768 0.2664
27/0 7.332 0.2886
- 7.895 0.3108
26/0 8.459 0.3330
4 - 9.023 0.3553
25/0 9.587 0.3775
24/0 10.151 0.3997
- 10.715 0.4219
5 23/0 11.279 0.4441
22/0 11.843 0.4663
- 12.407 0.4885
21/0 12.971 0.5107
6 20/0 13.535 0.5329
- 14.099 0.5551
19/0 14.663 0.5773
18/0 15.227 0.5995
7 - 15.791 0.6217
17/0 16.355 0.6439
16/0 16.919 0.6661
- 17.483 0.6883
8 15/0 18.047 0.7105
14/0 18.611 0.7327
- 19.175 0.7549
13/0 19.739 0.7771
9 12/0 20.303 0.7993
- 20.867 0.8215
11/0 21.430 0.8437
10/0 21.994 0.8659
10 9/0 22.558 0.8881
10¼ - 23.122 0.9103

Lignes Size Millimeters Inches
10½ 8/0 23.686 0.9325
10¾ - 24.250 0.9547
11 7/0 24.814 0.9770
11¼ 6/0 25.387 0.9992
11½ - 25.942 1.0214
11¾ 5/0 26.506 1.0436
12 4/0 27.070 1.0658
12½ 3/0 28.198 1.1102
12¾ 2/0 28.762 1.1324
13 0 29.326 1.1546
13½ 1 30.453 1.1990
14 2 31.581 1.2434
14¼ 3 32.046 1.2656
14¾ 4 33.273 1.3100
15 5 33.838 1.3322
15½ 6 34.955 1.3766
15¾ 7 35.529 1.3988
16 - 36.093 1.4210
16¼ 8 36.657 1.4432
16½ 9 37.221 1.4654
17 10 38.349 1.5098
17¼ 11 38.913 1.5320
17¾ 12 40.041 1.5764
18 13 40.605 1.5987
18½ 14 41.733 1.6431
18¾ 15 42.297 1.6653
19 - 42.861 1.6875
19¼ 16 43.425 1.7097
19½ 17 43.989 1.7319
20 18 45.117 1.7763
21 21 47.372 1.8651
22 23 49.628 1.9539
23 26 51.884 2.0427
24 29 54.140 2.1315
25 32 56.396 2.2204
26 34 58.652 2.3092
27 37 60.907 2.3980
28 40 63.163 2.4868
29 43 65.419 2.5756
30 45 67.675 2.6644