Decibel Converter Free Online
Convert between decibels (dB) and ratio in both directions. Power ratio uses 10 × log₁₀; voltage/amplitude ratio uses 20 × log₁₀. Used in audio, RF, signal processing, and acoustics.
P_out / P_in. dB = 10 × log₁₀(ratio)
V_out / V_in. dB = 20 × log₁₀(ratio)
Common dB References
Pro — bulk batch conversion, API access, history & favorites
API access · Priority queue · Team workspace
Related Tools
How It Works
Pick Your Unit or Preset
Choose your home unit using the dropdown or load a one-click preset. Defaults are sensible engineering values so you can start right away.
Enter a Value
Type a number — conversion runs as you type. Many tools have multiple input boxes (W & H, size & speed) — edit any of them and the rest recompute.
Read Every Equivalent
Below the main result, the All Units / Summary panel shows your value across every supported unit, with engineering context (FPS, ping, EM band, etc.) where relevant.
Decibel Converter Features
Power & Voltage
Two ratios in one tool. Power: dB = 10 × log₁₀(ratio). Voltage / amplitude: dB = 20 × log₁₀(ratio).
Audio Ready
+3 dB = double power. +6 dB = double voltage / SPL. +10 dB = perceived "twice as loud" in audio.
RF & Antennas
Antenna gain is in dBi. Cable loss in dB/m. Free-space path loss in dB. Link budget = sum of dB values.
15 References
Quick chart of common dB values from −60 (millionth) to +80 (100 million ×) so you can sanity-check.
Edit Any Field
Edit dB, power ratio, or voltage ratio — the other two update live.
100% Private
All math runs in your browser.
Free vs Pro
| Feature | Free | Pro |
|---|---|---|
| Full decibel conversion | ||
| Live conversion | ||
| All-units result panel | ||
| Bulk CSV / Excel conversion | — | |
| REST API access | — | |
| Custom precision settings | — |
Frequently Asked Questions
Power doubles → +3 dB (10 × log₁₀(2) ≈ 3.01). Voltage doubles → +6 dB (20 × log₁₀(2) ≈ 6.02). The factor of 2 between 10 and 20 comes from P = V² / R — when V doubles, P quadruples.
+3 dB = double the power (or RMS sound pressure squared). +6 dB = double the voltage / amplitude / SPL. +10 dB ≈ "perceptually twice as loud" in human hearing.
dBm is dB relative to 1 milliwatt — an absolute power level. 0 dBm = 1 mW; +30 dBm = 1 W; -100 dBm = 0.1 pW (typical Wi-Fi sensitivity floor). dB on its own is a relative ratio.
+10 dB SPL = 10× more sound power = roughly 2× perceived loudness for a typical listener. So 70 dB to 80 dB feels about twice as loud, even though it is 10× the power.
Because the dynamic range of real signals spans 10–14 orders of magnitude (whisper to jet engine, weak Wi-Fi to strong cable). Linear numbers become unwieldy; dB compresses the scale so 0–120 covers the whole range.