Designing websites used to be so easy. The standard was 640x480 on a 14" computer screen. Then 17" was the standard at 800x600. Then 1024x768.
Unfortunately it's anything by simple now.
Our data research tells us that there are between 42 - 48 normal screen sizes that visit jewelry related websites every month. You will usually see the 1024x768 resolution in the list near the top with about 20%, but that's far from a standard now.
In your Google Analytics you should check out your own statistics. From your Dashboard click on Visitors on the left, then under that click Browser Compatibility.
Take a look at the sub-options for Browsers to see what your visitors are using. Is Internet Explorer still #1?
Then take a look at the Operating Systems and don't be surprised if our see iPhone, Android, Bla...