Can you add two dB numbers together?
Yes you can!
For instance, if you cascade two 3 dB RF attenuation pads the resulting total attenuation is 6 dB.
Use the following calculator to calculate the sum of two dB numbers
Let’s say you have two RF amplifiers that are connected in series. The first one with a gain of 10 dB and the second with a gain of 30 dB. The total cascaded gain is 10+30 = 40 dB.
What does adding two dB numbers mean?
The deciBel equivalent of a number X is given by XdB = 10*Log10(X)
Similarly the dB equivalent of a number Y is YdB = 10*Log10(Y)
The dB equivalent of X*Y is 10*Log10(X*Y) = 10*Log10(X) + 10*Log10(Y)
The sum of two dB numbers is equivalent to the Log of the product of the two linear equivalents
In the above example, the first RF amplifier has a value of 10 dB which means it amplifies the signal by a factor of 10 (using the dB to Linear calculator).
The second RF amplifier has a value of 30 dB which means that it amplifies the signal 1000 times.
To calculate the effective gain we calculate the product of the two numbers: 1000*10 = 10,000.
The Logarithm of 10,000 is 10*Log10(10000) = 40 dB which represents the total or cascaded gain.The same number was found by adding the gain numbers in dB: 10 dB + 30 dB = 40 dB
Table of dB Sum vs Linear
This table provides the dB sum between two numbers and the product of the linear equivalent
- dBm Addition – Add two power values in dBm doesn’t follow the same rules as adding two dB values
- dB Difference – follows the same rules as addition