A watch case is the face of the watch, or the main area of the watch with the dial and any other instruments. Most women’s watches are approximately 26 mm to 36 mm in size, while most men’s watches are 37 mm to 42 mm in size. There are a few methods to measuring the diameter of a wristwatch case.

Use a small cloth measuring tape, such as the ones used for sewing. These measuring tapes can be purchased at most grocery, drug or sewing stores. Make sure the measuring tape includes millimeters on the measurement.

Place the end of the measuring tape (at “0”) on one side of the watch face. If there are any stems on the side of the watch face, start the measurement at that point.

Pull the measuring tape across the watch face at the widest width of the watch to the other side of the case, including any stems on the other side. Make sure the measuring tape is taut across the watch face.

Write down the number of the case width. This is the diameter of the watch case. Note that when sellers or retailers refer to the “watch size,” they are commonly referring to the thickness of the watch case or the length of the watch strap, not the diameter of the watch face.

Try using digital readers to measure the watch face. These tools are available at most watch repair stores or online, and use a small metal gauge to measure the watch face. The measurement is then displayed on a digital reader.