Power ratio in decibels (dB) 

10 log  10   (P  out  /P  in  )
 
 
Example:
Input power 100W and output power 1W
power ratio is -20dB
 
 
Power in dB (reference to 1 Watt) 
Y dB = 10 log  10   (X Watt)
 
 
Power in dBm (reference to 1 mWatt) 
Y dBm = 10 log  10   (X mWatts)
 
 
Example: 
0 dB = 30 dBm = 1 Watt
 

Summary
 
 
P (dBW) = 10 log (P/1 Watt)
 
 
P (dBm) = 10 log (P/1 mWatt)

Web Page Copyright: 亞洲大學資訊電機學院 連耀南 yaonanlien@asia.edu.tw  db.htm,  Tue Jun 13 18:53:29 CST 2023