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.
Frequently Asked Questions
What is the formula for dB gain?
Why is voltage gain multiplied by 20 while power gain is multiplied by 10?
What does a negative dB value mean?
Why use decibels instead of a plain ratio?
Common Tip Percentages
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Common Measurement Conversions for Everyday Use
| Quantity | US / Imperial | Metric Equivalent |
|---|---|---|
| 1 cup | 8 fl oz | 237 mL |
| 1 pint | 16 fl oz | 473 mL |
| 1 quart | 32 fl oz | 946 mL |
| 1 gallon | 128 fl oz | 3.785 L |
| 1 lb | 16 oz | 453.6 g |
| 1 ft | 12 in | 30.48 cm |