Adding dB Calculator

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

Note that while two dB numbers can be added or subtracted, the same is not true for dBm numbers. Here is a calculator to add or subtract dBm numbers.

Example Calculation

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 X_dB = 10*Log₁₀(X)

Similarly the dB equivalent of a number Y is Y_dB = 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

Related Calculators

• 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