Going from Sardinian to Italian (Italiano) has a composite linguistic distance of 18% (curated lexical data). Below is the dimension-by-dimension breakdown.
Shared vocabulary, cognates, and loanwords.
Morphology, syntax, word order, cases.
Shared sounds and phoneme inventory.
Latin → Latin
Indo-European ↔ Indo-European
The 5 languages with the lowest linguistic distance from Sardinian:
A quick 3-question check between Sardinian and Italian. No signup.