Srimad-Bhagavatam: Canto 11 - Chapter 1 - Verse 41
Sanskrit:
गायत्र्युष्णिगनुष्टुप् च बृहती पङ्क्तिरेव च ।त्रिष्टुब्जगत्यतिच्छन्दो ह्यत्यष्ट्यतिजगद् विराट् ॥ ४१ ॥
ITRANS:
gāyatry uṣṇig anuṣṭup cabṛhatī paṅktir eva catriṣṭub jagaty aticchandohy atyaṣṭy-atijagad-virāṭ
Translation:
The Vedic meters are Gāyatrī, Uṣṇik, Anuṣṭup, Bṛhatī, Paṅkti, Triṣṭup, Jagatī, Aticchanda, Atyaṣṭi, Atijagatī and Ativirāṭ.
Purport:
The Gāyatrī meter has twenty-four syllables, the Uṣṇik twenty-eight, the Anuṣṭup thirty-two, and so on, each meter having four more syllables than the previous one. Vedic sound is called bṛhatī, or most expansive, and thus it is not possible for ordinary living entities to understand all the technical details in this matter.