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The decibel (dB) is a logarithmic unit used throughout audio, electronics, and telecommunications to express a ratio between two values — because it compresses enormous ranges (like the human ear's sensitivity) into a manageable scale. This calculator finds the decibel gain or loss between an input and output value.
How it works
Choose whether your two values are a power ratio (like watts) or a voltage/amplitude ratio (like volts), enter the input and output values, and the calculator applies the matching formula: 10 log₁₀(ratio) for power, or 20 log₁₀(ratio) for voltage/amplitude.
- Enter ratio type.
- Enter input value.
- Enter output value.
- Click Calculate to see your results.
Examples
The same 10x ratio, two different dB values
A power ratio of 10:1 works out to 10 dB, but a voltage ratio of 10:1 works out to 20 dB — the formulas genuinely differ because power is proportional to voltage squared, not voltage directly.
Who should use it
- Audio engineering and acoustics coursework.
- Electronics and telecommunications signal-level calculations.
Industry applications
- Audio engineering and acoustics
- Electronics, RF, and telecommunications
Advantages
- Handles both the power and voltage/amplitude decibel formulas correctly.
- Simple, instant calculation for a widely-used unit.
Limitations
- Doesn't handle referenced decibel units (dBm, dBV, dB SPL, etc.) that compare against a fixed standard rather than two arbitrary values you provide.
Common mistakes to avoid
- Using the power formula (10 log₁₀) on a voltage ratio, or vice versa — this gives an answer exactly double or half what it should be.
- Forgetting that decibels are always a ratio between two values, not a standalone absolute measurement (unless referenced to a fixed standard value, like dBm or dBV, which this general calculator doesn't assume).
Best practices
- Double check whether your two values represent power or voltage/amplitude before picking the formula — this is the single most common source of error.
- Remember doubling power is +3 dB (not +10 dB) — a useful sanity-check figure to keep in mind.
Tips
- If you're not sure whether your figures are a power or voltage ratio, check the units — watts (W) means power, volts (V) means voltage/amplitude.