The ERF Placement Test
The Extensive Reading Foundation has developed its own placement test whereby students read passages at slowly increasing levels of difficulty and then report on how difficult each passage seems to be for themselves. The result is a number on the ERF 16-point scale which can then be correlated with your preferred book leveling system.
The test is available at: https://erfpt.ealps.shinshu-u.ac.jp
Other Placement Tests
You can use one of the following freely available placement tests to ascertain your students' initial level. Refer to the level chart on this page, or Rob Waring's comprehensive chart to equate their level to that of other publishers.
Cambridge Placement Test
Macmillan Level Test
Oxford Level Tests
Penguin Level Test
This table below shows a very rough correspondence between the Kyoto levels and other language level criteria. You can use this to determine initial (tentative) reading levels for your students. Note that it is desirable for their reading level to be somewhat below their actual current ability.