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How to Calculate Decibels

A decibel is a unit of measure of the ratio between two numbers and is used to measure power, voltage gain, sound pressure level and loudness. The most common measurements for power are watts and ohms. To calculate power measurements in decibels, you must first know the formulas for these power measurements and how to convert them to decibels.

Things You'll Need

  • Scientific calculator
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Instructions

    • 1

      Calculate power from ohms through the following formula: P=IR^2, where P=Power, I=Current and R=Resistance.

    • 2

      Define the bel as follows: Lb=log10 (P1/P0), where Lb=Bels and P1 and P0 are quantities.

    • 3

      Find the decibel, which is 0.1 bel, and can be expressed in the following formula: LdB=10log10 (P1/P0).

    • 4

      Express the decibel watt, which is the power of a signal in decibels relative to 1 watt and can be written as follows: dBW=10log10(W/1)=10log10(W), where dBW=Decibel Watts and W=Watts.

    • 5

      Combine these formulas into one conversion formula: dBW=10log10(W)=10log10(IR^2).

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