dB Calculator

Convert between dB and ratios, and convert dBm/dBW to watts. Includes Show Work and share links (on click).

How to Use

  1. Select a mode (Power Ratio, Voltage Ratio, dBm, or dBW).
  2. Enter the known value(s) (ratio, dB, or watts).
  3. Results update instantly in the output panel.
  4. Use “Copy Results” or “Share Link” from the Tool Menu when needed.
Calculator
Uses standard definitions: dB = 10·log10(P2/P1) and dB = 20·log10(V2/V1).
Example: +6 dB ≈ 2× voltage ratio, +3 dB ≈ 2× power ratio
Must be > 0. Use mode to choose power vs voltage definition.
Used for dBm/dBW conversions. Example: 1 mW = 0 dBm
Optional: compute dB relative to a custom reference (defaults by mode).
Show Work (step-by-step)
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Work is shown using base definitions (log10). Ratios must be > 0.

Reference Formulas

  • Power ratio to dB: dB = 10 · log10(P2 / P1)
  • Voltage (or current) ratio to dB: dB = 20 · log10(V2 / V1)
  • dB to power ratio: P2 / P1 = 10^(dB / 10)
  • dB to voltage ratio: V2 / V1 = 10^(dB / 20)
  • dBm to watts: P(W) = 10^((dBm − 30)/10)
  • Watts to dBm: dBm = 10 · log10(P(W)) + 30
  • dBW to watts: P(W) = 10^(dBW/10)
  • Watts to dBW: dBW = 10 · log10(P(W))
Tip: dB is relative (ratio). dBm and dBW are absolute power levels referenced to 1 mW and 1 W.

FAQ

Why is power “10·log10” but voltage is “20·log10”?

Because power is proportional to voltage squared in the same impedance. Taking log of a square introduces the factor of 2.

What does +3 dB mean?

Roughly double the power ratio (P2/P1 ≈ 2). For voltage ratio, +6 dB is roughly double (V2/V1 ≈ 2).

Can dB be negative?

Yes. Negative dB means attenuation (ratio less than 1).

What’s the difference between dBm and dBW?

dBm is referenced to 1 milliwatt; dBW is referenced to 1 watt. They differ by 30 dB for the same power value.

Tool Info

Last updated:

Updates may include unit handling, formatting improvements, and edge-case validation.