Ram Gayatri Mantra

The Hare Krishna Mantra

The Hare Krishna mantra is composed of Sanskrit names in the singular vocative case: Hare, Krishna, and Rama (in Anglicized spelling). It is a poetic stanza in anuṣṭubh meter (a quatrain of four lines (pāda) of eight syllables with certain syllable lengths for some of the syllables). 
The actual mantra in the Upanishad is as follows:[4]

Hare Rāma Hare Rāma

Rāma Rāma Hare Hare

Hare Kṛṣṇa Hare Kṛṣṇa

Kṛṣṇa Kṛṣṇa Hare Hare

— Kali-Saṇṭāraṇa Upaniṣad

When Sri Krishna Chaitanya Mahaprabhu promulgated the Mahamantra,
it was rendered with Krishna's name's first. 

Hare Kṛṣṇa Hare Kṛṣṇa

Kṛṣṇa Kṛṣṇa Hare Hare

Hare Rāma Hare Rāma

Rāma Rāma Hare Hare