In Jainism, “size of the universe” is explained very precisely, but in Jain terms, not in modern kilometers/light‑years.

1. Basic idea of the Jain universe (Lokākāś)

• The Jain universe is called Lok or Lokākāś.
• It is finite in size but eternal in time (no beginning, no end). ( jainknowledge.com)
• Its shape is like a standing human figure with legs apart and hands on the waist (lokapuruṣa). ( jainknowledge.com)

Inside Lok there are:

• Adho‑loka – lower region (7 hells)
• Madhya‑loka – middle region (we live here)
• Ūrdhva‑loka – upper heavens, and above them Siddhaśilā, the abode of liberated souls. ( jainknowledge.com)

Outside this Lokākāś is Alokākāś – empty space where no soul, karma or matter can exist. ( jainknowledge.com)

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2. Scriptural “size”: measured in rajju

Jain texts do not give the universe size in kilometers, but in a very huge unit called rajju.

From Jain cosmology: ( jainknowledge.com)

• 1 rajju = an unimaginably huge distance (defined using yojanas; exact number is so large that it is practically beyond imagination).
• The height of the universe (Lokākāś) is said to be 14 rajju.
• Width changes with height:

- Broad at the bottom - Narrow in the middle (where we are) - Broad again at the top

So, in simple language:

> Size of the Jain universe = a standing‑man–shaped space, about 14 rajju high.

This is the traditional, scriptural answer accepted in both Śvetāmbara and Digambara traditions. There may be small differences in some detailed numbers (exact yojanas etc.), but “14 rajju high, man‑shaped Lok” is common.

You can see some details on Jain cosmology and 14‑rajju loka here and about distance units here

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3. Why is it such a size and shape?

From Jain darshan:

1. Not created by anyone

- The universe is anādi‑ananta (without beginning and without end) and not created by a god. - Its size and shape are natural, not decided or changed by anyone. ( jainknowledge.com)

1. This particular shape is where all six dravyas exist together

Within this fixed Lokākāś: - Jīva (souls) - Pudgala (matter) - Dharma dravya (medium of motion) - Adharma dravya (medium of rest) - Ākāśa (space) - Kāla (time)

are all present and can interact. Outside (Alokākāś), only empty space exists, no jīva, no pudgala, no karma. So exactly this much space is “usable” for worldly existence; beyond that, nothing worldly can function.

1. Fixed, beginningless structure

Just as: - the nature of soul is to know and see, - the nature of fire is to burn,

similarly, the nature of the universe is to have: - this fixed shape, - this fixed finite extent (14 rajju), - and to continue eternally, going only through changes of states (ups and downs in time‑cycles), not changes in overall size. ( jainknowledge.com)

So the answer to “Why is it such?” in pure Jain terms is:

> Because that is the eternal, beginningless nature of Lokākāś. It is not designed or altered by anyone; its fixed size and shape are part of the eternal reality described by the Kevalajñānīs and preserved in Jain scriptures.

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In summary:

• Size: Finite, 14 rajju high, shaped like a standing person, divided into lower, middle, upper worlds, with Siddhaśilā at the very top.
• Why: This is the eternal natural form of the universe; it is neither created nor changeable, only the beings and conditions inside it keep changing according to karma.