Decibel Calculator
Calculate decibels (dB) from voltage ratios, power ratios, or amplitude ratios — and convert dB values back to linear ratios. Covers dBV, dBm, and dBW standards.
20.0000 dB
How to use the decibel calculator
Compute dB from a ratio of powers (10 log) or voltages/amplitudes (20 log).
Formula & explanation
dB(power) = 10 × log10(P1/P2). dB(voltage) = 20 × log10(V1/V2).
Examples
Doubling power = +3 dB. Doubling voltage = +6 dB.
Frequently asked questions
- What is a decibel?
- A decibel (dB) is a logarithmic unit expressing the ratio between two values. It is used for power and amplitude comparisons in audio, electronics, and communications.
- Why does doubling power equal +3 dB but doubling voltage equal +6 dB?
- Power is proportional to voltage squared (P ∝ V²), so the voltage formula uses 20 log instead of 10 log. A ×2 voltage ratio gives 20 × log₁₀(2) ≈ 6 dB, while a ×2 power ratio gives 10 × log₁₀(2) ≈ 3 dB.
- What does a negative dB value mean?
- A negative dB value means the numerator is smaller than the denominator — i.e. there is attenuation or loss rather than gain.
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