Which meter is used in these lines from Shakespeare's Sonnet 18?

Shall I compare thee to a summer's day?

Thou art more lovely and more temperate:

Rough winds do shake the darling buds of May,

The meter for Sonnet 18 is the same used for all of Shakespeare's sonnets: iambic pentameter.

The iambic pentameter indicates the rythm of the poem is that of an unstressed syllable followed by a stressed syllable (iambic), which is repeated 5 times in each line (pentameter).

For example:

Shall I compare thee to a summer's day?

There are 5 unstressed and 5 stressed syllables.