The easiest way to figure out if a line, or an entire poem, is written in pentameter is to start with line one and read it aloud. If the line has ten syllables, then it is pentameter. This does not mean that the entire poem is going to be structured in the same way. If the poet does not consistently use ten syllables, it is more likely than not that the poem is written in free verse. Or that the poet chose to utilize numerous metrical patterns throughout their text.