Wood screws are used for a wide variety of woodworking projects. They come in many different sizes, so how do you know what size screw you are using? To determine the size screw you are using, you will need to measure the length and shank and then compare those measurements to a screw chart. The chart will allow you to determine the gauge of the screw. Screws are measured in gauges from zero through 24.
Place the screw on a work surface. Measure the screw from the tip to the head's widest point using the steel ruler. This is the length of the screw.
Place the calipers of the micrometer on the shank of the screw. Adjust the calipers to get an accurate measurement of the screw shank diameter. Note the measurement on the micrometer. This is the shank size.
Refer to a wood screw chart. The gauge is based on the screw measurements in step two. The diameter will be any where from .060 to .372-inches for screw gauges zero to 24, respectively.
Hang a wood screw chart near your work bench. When your project calls for a certain size screw, you can measure it and refer to the chart.