From memory it is not a calculator as such.
When you are creating listing when you get to shipping details page if you select a shipping service and punch in correct size and weight it should show you calculated price for level of shipping requested.
But even if you get this to show it is usually sadly inaccurate ( as is eBay's for that matter).
I usually just take a best guess based in experience and put a flat rate shipping price in my ads.
Good luck
When you are creating listing when you get to shipping details page if you select a shipping service and punch in correct size and weight it should show you calculated price for level of shipping requested.
But even if you get this to show it is usually sadly inaccurate ( as is eBay's for that matter).
I usually just take a best guess based in experience and put a flat rate shipping price in my ads.
Good luck