Śrīmad-Bhāgavatam · Text 3.11.41
Who is speaking and story frame
दशोत्तराधिकैर्यत्र प्रविष्ट: परमाणुवत् ।
लक्ष्यतेऽन्तर्गताश्चान्ये कोटिशो ह्यण्डराशय: ॥ ४१ ॥
daśottarādhikair yatra
praviṣṭaḥ paramāṇuvat
lakṣyate ’ntar-gatāś cānye
koṭiśo hy aṇḍa-rāśayaḥ
The layers or elements covering the universes are each ten times thicker than the one before, and all the universes clustered together appear like atoms in a huge combination.
Read Śrīla Prabhupāda's purport on Vedabase.io