It's about 12mm. If made into a bracelet, the inner diameter would be about 14.5cm. If you'd like it made into a bracelet, I'll assemble it for free, so feel free to ask＾＾ You can also combine it with other stones in the store＾＾ Perfect for handmade projects! It's 50 yen off for every 2 items, so please take advantage of it♡ To prevent trouble〜 There may be natural cracks, scratches, dents, and inclusions that are characteristic of natural stones◡̈⃝︎⋆︎* There will inevitably be an error of about plus or minus 0.5mm, so I've written "about ○mm"♪ There's nothing as perfect as artificial glass, so please understand◡̈⃝︎⋆︎*