Have a trusty tape measure close by when you have anything listed on Ebay.  It's totally amazing what questions potential buyers will ask about size.  This can be for simple things that are of standard size.  I guess standard can mean different things to different people.  I've learned to measure everything I list, and still I'll get questions about the size.  One picture is worth a 1,000 words they say, but not necessarily so with Ebay.