Yes, all sonnets are.
A fourteen line poem in iambic pentameter (in English) is very likely to be a sonnet. It isn't guaranteed to be a sonnet - but the first thing you check is whether it is a sonnet or not.
English sonnet
sonnet
Yes, Sonnet 73 is written in iambic pentameter. It consists of 14 lines, with each line containing 10 syllables following the pattern of unstressed syllable followed by a stressed syllable (iambic) and five metrical feet in total (pentameter).
A Shakespearean Sonnet is a 14-line poem written in iambic pentameter and with a rhyme scheme of ababcdcdefefgg.
iambic pentameter
A sonnet -- particularly of the Italian or Shakespearean variety -- is comprised of fourteen lines of iambic pentameter.
A sonnet consists of fourteen lines of iambic pentameter. There are two main types of sonnets: the Petrarchan (or Italian) sonnet and the Shakespearean (or English) sonnet.
Sonnet.
Iambic pentameter.
Iambic pentameter.
iambic pentameter