How to Determine the Size of Your Watch

Watch movements are measured in an arcane English system of measurement called the Lancashire system or Lancashire Gauge**. In this system, 1 5/30th inches is the "base" measurement and is called 0-size. Each 1/30th of an inch adds 1 (or subtracts 1) to this base. A watch is measured through the center of the lower plate of the movement (the dial side). If the movement is asymmetrical, say oval or rectangular, it is measured at its narrowest point. Note that the case is NOT included in this measurement, only the movement. Measuring the dial is usually a fair approximation of the lower plate measurement.

Watch Size	Fractional Inch	Decimal Inch	Lignes	Millimeters
18	1 23/30	1.766	19.87	44.86
17	1 22/30	1.733	19.50	44.02
16	1 21/30	1.700	19.12	43.17
15	1 20/30	1.666	18.75	42.33
14	1 19/30	1.633	18.37	41.48
13	1 18/30	1.600	18.00	40.63
12	1 17/30	1.566	17.62	39.79
11	1 16/30	1.533	17.25	38.94
10	1 15/30	1.500	16.87	38.09
9	1 14/30	1.466	16.50	37.25
8	1 13/30	1.433	16.12	36.40
7	1 12/30	1.400	15.75	35.55
6	1 11/30	1.366	15.37	34.71
5	1 10/30	1.333	15.00	33.86
4	1 9/30	1.300	14.62	33.01
3	1 8/30	1.266	14.25	32.17
2	1 7/30	1.233	13.87	31.32
1	1 6/30	1.200	13.50	30.47
0	1 5/30	1.166	13.12	29.63
2/0	1 4/30	1.133	12.75	28.78
3/0	1 3/30	1.100	12.37	27.93
4/0	1 2/30	1.066	12.00	27.09
5/0	1 1/30	1.033	11.62	26.24
6/0	1 0/30	1.000	11.25	25.39
7/0	29/30	.966	10.87	24.55
8/0	28/30	.933	10.50	23.70
9/0	27/30	.900	10.12	22.85
10/0	26/30	.866	9.75	22.01
11/0	25/30	.833	9.37	21.16
12/0	24/30	.800	9.00	20.31
13/0	23/30	.766	8.62	19.47
14/0	22/30	.733	8.25	18.62
15/0	21/30	.700	7.87	17.77
16/0	20/30	.666	7.50	16.93
17/0	19/30	.633	7.12	16.08
18/0	18/30	.600	6.75	15.23
19/0	17/30	.566	6.37	14.39
20/0	16/30	.533	6.00	13.54
21/0	15/30	.500	5.62	12.69
22/0	14/30	.466	5.25	11.85
23/0	13/30	.433	4.87	11.00
24/0	12/30	.400	4.50	10.15
25/0	11/30	.366	4.12	9.31
26/0	10/30	.333	3.75	8.46