How to Measure a Pocket Watch?

To get the most precise pocket watch measurement, you will want to measure the movement’s lower plate below the dial. Since the dial often extends beyond the movement, it’s not an accurate way of measuring the size of your pocket watch, however, with a well-trained eye it might be close enough to guess.

Movement vs Case Size

It’s important to know that a pocket watch size has nothing to do with the outside case diameter. A pocket watch can have various case sizes depending on the style and design. The case diameter is good for knowing how big the pocket watch is overall, if it will fit in your vest or watch pocket for example, but it is not relevant to the chart above.

Common Pocket Watch Sizes

Pocket watches come in all different sizes, but the most common will be 18s, 16s and 12s for men, or 0s, 6s and 8s for ladies pocket watches. 10s or 12s can be considered unisex. Early on, railroad pocket watches were allowed to be 18s or 16s, but eventually were required to be 16s.

What Does the S Mean?

The S next to the number just means “Size”. For example 18 is the same as 18S, and also the same as 18-Size. This S is usually added to the number so that you know it’s a size number rather than a jewel count. Similarly, you may also see something like 7J for jewels. Some dealers and enthusiasts might type these sizes differently.

Pocket Watch Sizes

These measurements are not related to the size of the case or dial. This chart converts American pocket watch sizes from inches to millimeters. You will notice from the chart below that pocket watches are typically measured in 30ths of an inch, also known as the “Lancashire Gauge” adopted from England. Remember, the sizes below refer to the movement size.

Size Inches Millimeters
1 27/30″ (1.9″)
20s 1 25/30″ (1.83″)
18s common 1 23/30″ (1.766″)
17s 1 22/30″ (1.733″)
16s common 1 21/30″ (1.700″)
1 19/30″ (1.633″)
12s common 1 17/30″ (1.566″)
10s common 1 15/30″ (1.500″)
8s common 1 13/30″ (1.433″)
6s common 1 11/30″ (1.366″)
0s common 1 5/30″ (1.166″)
1 3/30″ (1.100″)
14/15″ (0.933″)
4/5″ (0.800″)
3/5″ (0.600″)

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10 Responses

  1. Michelle

    Thanks for sharing this chart. It will be very helpful when shopping for junk watches for use in Steampunk jewelry and art.

    • Keystoner

      6 is 34.7mm and 60 would be over 100mm probably. Did you see 60? that doesn’t even exist.

  2. Phil

    Hi, I am confused. All the data I have researched including the table here informs me that according to the serial number, the Elgin 7 jewel pocket watch I have is a 1927 16s, yet when I measure the actual movement it has a size of 40.6 mm indicates it is a 13s size. Can someone please clarify what’d size the movement is that I have. Cheers. Phil

    • Keystoner

      You’re probably measuring it incorrectly. Most people make the mistake of measuring the movement side. Like these guys said at the top of the page you have to measure the dial side.

  3. Kyle Sheridan

    What is the S on some of the pocket watch sizes? Can someone please tell me? Is there a difference between 18 and 18S? Thank you!

    • Kyle Sheridan

      Nevermind, sorry I just saw the chart and didn’t bother reading the rest of the post. I understand now, thanks!


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