The Size of Happiness is a book in six sections, the titles of which hint at the richness and variety of its contents.

What the Amorini Know comes at love from a dozen angles, though it is especially concerned with the many ways it has of going wrong; Horses of Poseidon uses ancient myths to debate modern subjects – amongst them, the difficulty of faith, the question of how far we can penetrate and bend to our purpose the forces of nature, and the relative significance of a fictional character and a real person; An Older Beast tackles the rather older subject of "sad mortality"; and in Clay and Flame and Managing the Planets – the opening and closing sections of the book – Warren's poems ask how to manage the morsel of world we think we own, how to catch beauty in a net, how to find the most elusive thing of all – happiness.