The poem is written in iambic tetrameter, with rhyme scheme AA BB CC etc. The first stanza is ten couplets long, the second six, and the third seven.

Here is an excerpt, from the second stanza:

But at my back I always hear
Time’s wingèd chariot hurrying near;
And yonder all before us lie
Deserts of vast eternity.
Thy beauty shall no more be found,
Nor, in thy marble vault, shall sound
My echoing song: then worms shall try
That long preserved virginity,
And your quaint honour turn to dust,
And into ashes all my lust:
The grave’s a fine and private place,
But none, I think, do there embrace.

Read the full poem here:
To His Coy Mistress – gutenburg e-text