12.8 mm across on the top deck north to south. US Size 7 1/4 or British / Australian size O. Ring can be re sized for free and will take. About 10 days to complete.BRIGHTNESS IS RATED ON A ONE TO FIVE SCALE AS. Opal is Brilliant and Color Jumps out of the stone at you at arms length. Opal is Bright and Color is Crisp and Sharp at arms length. Opal has Good Color at arms length. Opal has Fair color but Nothing Special. Opal has Color but is Fairly Dull. Photos were taken under a 40 watt soft white light, without a flash and are NOT ENHANCED IN ANY WAY! I have been making Opal Jewelry for 27 years and stand behind all my work.