The poem consists almost entirely of quatrains, or four-line stanzas. There are 16 quatrains followed by the final stanza, which consists of five lines rather than four. Each stanza is in iambic meter. An iambic foot comprises an unstressed syllable followed by a stressed syllable. The stanza alternates tetrameter lines, consisting of four feet (Lines 1 and 3) with trimeter lines, comprising three feet (Lines 2 and 4):

She had a rustic, woodland air,

And she was wildly clad:

Her eyes were fair, and very fair,

—Her beauty made me glad (Lines 9-12). 

This type of stanza is called a ballad stanza; in such stanzas usually only the second and the fourth line rhyme, but Wordsworth adapted the popular form to suit his own preferences. 

Wordsworth varies the meter slightly on a number of occasions. In a few lines, he substitutes a trochee for an iamb in the first foot. A trochee consists of a stressed syllable followed by an unstressed syllable, as in “Sisters and brothers” (Line 13) and “Quick was the little Maid’s reply” (Line 63).