How to convert Wifi signal strength from Quality (percent) to RSSI (dBm)?

Question

How should I convert Wifi signal strength from a Quality in percentage, usually 0% to 100% into an RSSI value, usually a negative dBm number (i.e. -96db)?

Answer 1

Ok.. I agree...but why is then:

 Quality=29/100  Signal level=-78 dBm
 Quality=89/100  Signal level=-55 dBm
 Quality=100/100 Signal level=-21 dBm

this does not agree with the formula percentage=quality/2 - 100.