What is the "public ratio" of buildings in Taiwan?

Taiwan's building area is calculated in "pings", and 1 ping is approximately 35.6 square feet. The public ratio is the area of public space and facilities shared by all residents outside what we call "saleable area", which is generally 20% ~ 40%. For example, a unit with a building area of 20 pings, which is 20 x 35.6 = 712 feet,

If the unit's public ratio is 30%, the saleable area is 712 x 70% = 498 feet. Therefore, the larger the public ratio, the smaller the practical area.