What visa do I need if I'm traveling from Australia to Thailand for less than 30 days with multiple entries?

You dont need to apply for any visa

Thai embassy website for info is reliable.

Aussies still can get a visa excemption stamp valid for 60 day's (still at this stage) can I ask how many times visiting Thailand this year? You could apply for a METV. This visa allows you to enter Thsiland within a 6 month period multiple times for each stay up to 60 days with the opportunity to apply for a additional 30 days.

From 1 August TDAC is now completed within the THIM app - developed by Thai Police .

Tony Martin’s info is correct. Beware of other responses - much opinion but all here-say unfortunately.

Fill out TDAC form 3 days before you arrive, flighr details, and where you a staying hotel or motel and location

If you have an Australian passport you can currently enter for 60 days using the Visa exemption scheme so no visa is required but because your wanting to leave and return multiple times in the same year it's probably wise to apply for The Thailand Multiple-Entry Tourist Visa (METV) is valid for 6 months from the date of issue and allows unlimited entries. Each stay is capped at 60 days, though it can be extended once for an additional 30 days at a local immigration office.

No visa needed. You will get visa exemption on entry.

The TDAC will need to be submitted within the 3 day period before entry. You will need to do this for every time you enter the country.

If you have a history of long stays or overstays in Thailand then this advice may not be right.