In Jainism (and other ancient Indian systems), 1 yojan is a big unit of distance.

From Jain cosmology and commentaries:

• 1 yojan ≈ about 8 miles
• which is ≈ 12–13 kilometers (many Jain scholars commonly use ~13 km).

Different texts and traditions may give slightly different exact numbers, but for Jain study and basic understanding, you can safely take:

1 yojan ≈ 12–13 km (around 8 miles).

You can read a simple Jain explanation here