How to Calculate DB Ohms

Written by paige turner
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How to Calculate DB Ohms
Decibels represent a logarithmic ratio. (decibel scale image by Vladislav Gajic from

Decibel, or dB, is a logarithmic unit of measurement that represents a ratio of power gain or loss in communication systems. Decibels describe numbers that vary greatly in magnitude. The comparison of the two numbers can be simplified by converting the ratio of the two numbers into a logarithm. The original unit of measurement is typically used along with dB to describe the final value. Decibels are used for communication system measurements such as gain and light-budget calculations.

Skill level:


  1. 1

    Calculate dB with the following formula:

          dB = 10 log P2 / P1.

    Use this formula if you have the value of reference power, or P1, and calculated power, or P2.

  2. 2

    Calculate dB with the formula:

         dB = 10 log ((V2^2)/R2  /   (V1^2)/R1.

    Use this formula if you have the values for calculated voltage (in volts) and resistance (in ohms), or V2 and R2 as well as reference voltage and resistance, or V1 and R1.

  3. 3

    Simplify the equation in step 2 by assuming that R1 is equal to R2. Calculate dB with the formula:

        dB = 10 log ((V2^2) / (V1^2))

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