s="pͪoͣnͬpͣoͥnͭpͣa͡inͥ"
s.encode("UTF-8").grapheme_clusters.size;
→10

参考文献＞＜；
Ruby で文字数を数える #Ruby - Qiita
https://qiita.com/Nabetani/items/93e9af28bd9a2bea03f0