Sir Orfeo consists of octosyllabic lines. This means that each line has eight syllables:

There down in shade they sat all three,

beneath a fair young grafted tree;

and soon it chanced the gentle queen

fell there asleep upon the green (Lines 69-72).

There are some exceptions, since a small number of lines have nine syllables, for example, “concerning adventures in those days” (Line 15), “Of adventures that did once befall” (Line 21), “saw sixty ladies on horses ride” (Line 304), and “who had been royal, and high, and fair” (Line 326).

The meter is mostly iambic. An iambic foot comprises an unstressed syllable followed by a stressed syllable. This yields a four-stress line, also known as a tetrameter: “Of all | the things | that men | may heed / ’tis most | of love | they sing | indeed” (Lines 11-12), and “they took | their harps | in their | delight / | and made | a lay | and named | it right” (Lines 19-20).

In the original Middle English, the initial unstressed syllable sometimes does not appear, giving a line of seven syllables, but Tolkien’s translation usually adds that missing syllable to create the iambic meter.