The Brahma-saṁhitā (5.48) says:

yasyaika-niśvasita-kālam athāvalambya jīvanti loma-vilajā jagad-aṇḍa-nāthāḥ viṣṇur mahān sa iha yasya kalā-viśeṣo govindam ādi-puruṣaṁ tam ahaṁ bhajāmi

The origin of the material creation is Mahā-Viṣṇu, who lies in the Causal Ocean. While He sleeps in that ocean, millions of universes are generated as He exhales, and they are all annihilated when He inhales. This Mahā-Viṣṇu is a plenary portion of a portion of Viṣṇu, Govinda ( yasya kalā-viśeṣaḥ ). The word kalā refers to a plenary portion of a plenary portion. From Kṛṣṇa, or Govinda, comes Balarāma; from Balarāma comes Saṅkarṣaṇa; from Saṅkarṣaṇa, Nārāyaṇa; from Nārāyaṇa, the second Saṅkarṣaṇa; from the second Saṅkarṣaṇa, Mahā-Viṣṇu; from Mahā-Viṣṇu, Garbhodakaśāyī Viṣṇu; and from Garbhodakaśāyī Viṣṇu, Kṣīrodakaśāyī Viṣṇu. Kṣīrodakaśāyī Viṣṇu controls every universe. This gives an idea of the meaning of ananta, unlimited. What is to be said of the unlimited potency and existence of the Lord? This verse describes the coverings of the universe ( saptabhir daśa-guṇottarair aṇḍa-kośaḥ ). The first covering is earth, the second is water, the third is fire, the fourth is air, the fifth is sky, the sixth is the total material energy, and the seventh is the false ego. Beginning with the covering of earth, each covering is ten times greater than the previous one. Thus we can only imagine how great each universe is, and there are many millions of universes. As confirmed by the Lord Himself in Bhagavad-gītā (10.42) :

athavā bahunaitena kiṁ jṣātena tavārjuna viṣṭabhyāham idaṁ kṛtsnam ekāṁśena sthito jagat

“But what need is there, Arjuna, for all this detailed knowledge? With a single fragment of Myself I pervade and support this entire universe.” The entire material world manifests only one fourth of the Supreme Lord’s energy. Therefore He is called ananta.