dB to Power Ratio Calculator

How it is calculated

You enter a level difference in decibels (dB). The tool inverts the decibel definition twice. For power, ratio = 10^(dB ÷ 10); for amplitude (voltage, current or sound pressure), ratio = 10^(dB ÷ 20). The two results differ because power goes with the square of amplitude: a ratio of 10 in power is a ratio of about 3.16 in amplitude.

Positive dB gives ratios above 1 (gain), 0 dB gives exactly 1 and negative dB gives ratios below 1 (loss). Results are shown with four decimals, so a large attenuation such as −90 dB displays as 0.0000 even though the true ratio is not zero. The value is a pure ratio, with no reference level, so it applies to dB relative to something (gain, loss) rather than to absolute scales such as dBm or dBSPL on their own.

Common mistakes

• Using the power formula for voltage or sound pressure. A 6 dB increase is about 3.98 times in power but only about 2.00 times in amplitude, so choose the amplitude figure when you mean volts or pascals.
• Entering a ratio instead of decibels. The field is the dB value, so 2 means +2 dB (a power ratio of 1.5849), not a doubling.
• Dropping the minus sign for a loss. 3 dB and −3 dB are 1.9953 and 0.5012 in power, which are not the same.
• Adding ratios when combining stages. Stages in series add in dB but multiply as ratios, so convert before you multiply, not after you add.
• Reading 0.0000 as exactly zero. With four decimals, very large losses are rounded away; a −90 dB path still passes a tiny non-zero fraction of power.