Italian sonnets consist of 14 lines, while English sonnets consist of 16 lines.
Italian sonnets have a specific rhyme scheme consisting of two quatrains (4 lines each) having the rhyme scheme ABBA ABBA and two tercets (3 lines each) with the rhyme scheme CDC DCD or CCD CCD. English sonnets adhere to a different rhyme scheme: ABAB CDCD EFEF GG.
Italian sonnets traditionally have a "turn" or "volta" after the eighth line, where the poem's theme shifts or a contrasting idea is introduced. This is less pronounced in English sonnets, which can have a less clear division.
While Italian sonnets do not have a mandatory form of meter (though traditional forms like iambic pentameter were commonly used), English sonnets are predominantly written in iambic pentameter, which is a poetic rhythm consisting of five iambs (unstressed-stressed syllables) in each line.
Lastly, Italian sonnets were the primary sonnet form in Italy, originating in the 13th century and becoming popularized by poets such as Dante Alighieri and Petrarch. English sonnets, on the other hand, developed in England during the Renaissance period, notably popularized by poets like Henry Howard, Earl of Surrey, and Sir Thomas Wyatt.