dB Difference Calculator

This calculator finds the difference between two deciBel (dB) values.

Example Calculation

Let’s say you have an RF attenuator with a value 30 dB followed by an amplifier with gain 20 dB.

• The total attenuation is 30 dB – 20 dB = 10 dB
• The total amplification is 20 dB – 30 dB = -10 dB

What does dB difference 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 difference between two dB numbers is equivalent to the Log of the ratio of the linear equivalent of the two.

In the above example, the RF attenuator has a value of 30 dB which means it attenuates the signal by a factor of 1000. Alternatively, it amplifies the signal by -30 dB = (1/1000).

The RF amplifier has a value of 20 dB which means that it amplifies the signal 100 times.

To calculate the effective gain we calculate the product of the two numbers: (1/1000)*100 = 1/10.

The Logarithm of 1/10 is 10*Log₁₀(1/10) = -10 dB which represents the total or cascaded gain.

The same number was found by adding the gain numbers in dB: 20 dB – 30 dB = -10 dB

Table of dB Difference vs Linear

This table provides the dB difference between two numbers and the ratio 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 Addition – follows the same rules as subtraction