How to use the dB Gain Calculator
The decibel (dB) is a logarithmic unit that expresses the ratio between two power, voltage, current, or other amplitude-like quantities. Rather than saying an amplifier multiplies power by 1,000, engineers say it provides "30 dB of gain" — a compact way to describe enormous ranges of signal strength and to combine gains and losses in a chain by simple addition. This calculator takes a reference (input) value and a measured (output) value and converts their ratio into decibels.
Power vs. voltage decibels — why 10 log₁₀ vs. 20 log₁₀
For power quantities, the gain in decibels is dB = 10 × log₁₀(P₂ / P₁). For voltage, current, sound pressure, or any other amplitude quantity, it's dB = 20 × log₁₀(V₂ / V₁). The factor changes because power is proportional to the square of voltage (P = V²/R): substituting V² for P inside the power formula gives 10 × log₁₀(V₂²/V₁²), and the exponent of 2 pulls out of the logarithm as a multiplier, turning the 10 into 20. The result is that a voltage ratio and its squared power ratio (assuming equal impedance) always land on the exact same dB value — this calculator computes both the power-domain and voltage-domain ratio from whichever one you enter so you can see that equivalence directly.
Reading the result and common reference points
A positive dB value means the output is larger than the input (amplification/gain); a negative value means the output is smaller (attenuation/loss); 0 dB means the ratio is exactly 1, i.e. no change. A few landmarks are worth memorizing: +3 dB is roughly double the power, +6 dB is roughly double the voltage, +10 dB is exactly 10× the power, and +20 dB is exactly 10× the voltage (which is also 100× the power). These same relationships work in reverse for attenuation: -3 dB is roughly half the power, and -20 dB is one-tenth the voltage. In audio and RF work you'll also see dB used with a fixed reference, such as dBm (relative to 1 mW) or dBV (relative to 1 V) — those are just this same gain formula applied against a standard reference value instead of your own input measurement.