# Conversion between linear and decibel scale

This window helps translating between logarithmic decibel scale and linear scale. While concerning optics mainly power levels are of interest, the second part of the window also calculates voltage ratios.

In the first section power ratios are translated between linear and decibel scale. A ratio can be entered directly or by giving a certain power level together with a power reference. If the one of the units dBK, dBW, dBm or dBf is chosen, the reference level is fixed to 1 kW, 1 W, 1 mW or 1fW, respectively.
The relation between power ratio and dB scale is:

• ratio = input / reference
• 1 dB = 10*log(ratio)

Voltage ratios first have to be squared and thus transferred into power ratios before translating them into decibels. Specifying a resistance additional relates the voltage input to the power input in the first section. Certain dB units require fixed reference voltages and reference resistances.
The relations are:

• ratio = input / reference
• 1 dB = 10*log(ratio^2) = 20*log(ratio)
• power = voltage^2 / termination