How Large is the Wurm Client?
The Wurm client itself is about 8 MB, but it will download a graphics (521 MB) and a sound pack (106 MB), which adds up to a total of 635 MB. The actual number will vary over time as client, sound and graphics are updated regularly.
The updater is smart enough to only download the new/changed parts and not re-download the entire packs when they are updated.