When it comes to the size of tubeless rim tape you need, it depends on two factors.
The tape width has to be at least 3 to 5mm wider than your rim’s internal width. The additional width allows for the rim tape to run 1 to 2 mm up the rim’s sidewalls to provide better coverage.
You can get the internal width information from your wheelset manufacturer’s website.
Generally, tubeless rims for road bikes have an internal width of 17, 19, 21, 23, or 25mm. Newer wheelsets usually have wider internal widths to accommodate wider tires.
For example, the latest Zipp 303 Firecrest has an internal diameter of 25mm and thus would require a rim tape width between 28 to 30mm.
Rim tapes come in lengths of around 10m. Each 700c rim (622mm in diameter) has a circumference of 1.95m.
Each rim would require around 2.1 to 2.2 meters of rim tape, taking into consideration some overlap between both ends of the tape. So, you can apply up to four rims for each tape.
There is also a workshop variant of the rim tape which has lengths up to 60 meters.