Don't know your ring size? Or maybe you need a way to find out your girlfriend or boyfriend ring size without asking. No worries. Here's an easy way to figure it out.
Just grab a favorite ring and measure the interior diameter. You can use either inches or millimeters. (I recommend millimeters since it more easily provides greater granularity.) Cross reference this measurement against the table below and - tada! - you have your ring size.
Of course, there are many sizes in between whole and half sizes. If you want to be more precise, you can reference this more detailed ring size conversion chart.