20 Log dB Calculator

This tool calculates the deciBel equivalent of a real number.

It uses the formula PdB = 20 * Log(X) for the calculation.

Enter X in the tool below and it will compute the dB equivalent


The expression “20 log dB” typically refers to a formula used to calculate the decibel (dB) level of a signal, specifically in terms of voltage or current ratios, rather than power. The full expression is:

dB = 20*Log10(V1/V0)


  • V1 and V0 are the voltages (or currents) being compared.
  • Log10 is the base-10 logarithm.

This formula is used when the relationship between the quantities is linear. For example, if V1 is twice V0, the dB calculation would give approximately 6 dB as an answer.

This is applied in contexts where voltage or current ratios are relevant, such as in audio engineering and telecommunications. It differs from the formula for power ratios, which uses 10 instead of 20:

dB = 10*Log10(P1/P0)

Here, P1 and P0 are power levels being compared, and the factor of 10 is used because power is proportional to the square of the voltage or current in a resistive load.