Srimad Bhagavatam Canto 05, Chapter 01, Text 33

SB 5.1.33

ksarodeksu-rasoda-suroda-ghrtoda-ksiroda-dadhi-mandoda-suddhodah sapta jaladhayah sapta dvipa-parikha ivabhyantara-dvipa-samana ekaikasyena yathanupurvam saptasv api bahir dvipesu prthak parita upakalpitas tesu jambv-adisu barhismati-patir anuvratanatmajan agnidhredhmajihva-yajñabahu-hiranyareto-ghrtaprstha-medhatithi-vitihotra-samjñan yatha-sankhyenaikaikasminn ekam evadhi-patim vidadhe.
 
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
The seven oceans respectively contain salt water, sugarcane juice, liquor, clarified butter, milk, emulsified yogurt, and sweet drinking water. All the islands are completely surrounded by these oceans, and each ocean is equal in breadth to the island it surrounds. Maharaja Priyavrata, the husband of Queen Barhismati, gave sovereignty over these islands to his respective sons, namely Agnidhra, Idhmajihva, Yajñabahu, Hiranyareta, Ghrtaprstha, Medhatithi and Vitihotra. Thus they all became kings by the order of their father.
 
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
It is to be understood that all the dvipas, or islands, are surrounded by different types of oceans, and it is said herein that the breadth of each ocean is the same as that of the island it surrounds. The length of the oceans, however, cannot equal the length of the islands. According to Viraraghava Acarya, the breadth of the first island is 100,000 yojanas. One yojana equals eight miles, and therefore the breadth of the first island is calculated to be 800,000 miles. The water surrounding it must have the same breadth, but its length must be different.
Srimad Bhagavatam Canto 05, Chapter 01, Text 32
Srimad Bhagavatam Canto 05, Chapter 01, Text 34