We add sizes to the listings and we are happy to add in measurements to the item specifics if there is a space for this. eBay actually requires sizes for clothing.
If you are Taking photos through the app when you finish taking the photos, you will come to the "Sell Your Item" page that asks for the condition of the item. If you are Uploading photos, this will be the last Upload page before you submit.
On that page, there is a section to provide Size, Gender and Color. There is also "Add Notes to Buyer (Optional)" which you can use to fill in additional information that you would like your customer to know. This is where you can add additional details, such as measurements and flaws or any special information.
Please note: Any notes that you put in the "Add Notes to Buyer" will appear in the description of the item on the listing.