What is the formula for Decibel (dB) Calculator?

Core formula: dB = 10·log10(P2/P1) = 20·log10(V2/V1) | dBm = 10·log10(P/1mW). The tool returns results instantly using this formula and the selected parameters.

What engineering notes should I keep in mind when using Decibel (dB) Calculator?

Power quantities use a factor of 10: dB = 10·log10(P2/P1); voltage / current quantities (equal impedance) use a factor of 20: dB = 20·log10(V2/V1). Rules of thumb: power +3 dB ≈ ×2, +10 dB = ×10; voltage / current +6 dB ≈ ×2, +20 dB = ×10. Absolute levels: 0 dBm = 1 mW, 0 dBW = 1 W, 0 dBV = 1 V, 0 dBu = 0.775 V, 0 dBμV = 1 µV. For a cascaded linear system (amplifiers / attenuators / filters) the total gain is the sum of the stage dB values, i.e. the multiplicative ratios mul…

Decibel (dB) Calculator

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Convert ratios, power and voltage to and from decibels: power ratio ↔ dB, voltage ratio ↔ dB, absolute power (dBm / dBW), voltage level (dBV / dBu / dBμV) and cascaded gain.

Key points

Decibel (dB) Calculator: Convert ratios, power and voltage to and from decibels: power ratio ↔ dB, voltage ratio ↔ dB, absolute power (dBm / dBW), voltage level (dBV / dBu / dBμV) and cascaded gain. Formula: dB = 10·log10(P2/P1) = 20·log10(V2/V1) | dBm = 10·log10(P/1mW). Enter parameters on the DD-CAT IDE online tool page to get results instantly, with a calculation-model diagram that updates with the inputs. Power quantities use a factor of 10: dB = 10·log10(P2/P1); voltage / current quantities (equal impedance) use a factor of 20: dB = 20·log10(V2/V1). Rules of thumb: power +3 dB ≈ ×2, +10 dB = ×10; voltage / current +6 dB ≈ ×2, +20 dB = ×10.

Inputs

dB = 10·log10(P2/P1) = 20·log10(V2/V1) | dBm = 10·log10(P/1mW)

Conversion typeReference power P1Reference for 0 dBMeasured power P2The ratio to the reference power determines dB

Calculation model (updates with parameters)

Power change ΔdB	+3.01 dB	dB = 10·log10(P2/P1)
Power ratio P2/P1	2 ×	P2 = P1 × 10^(dB/10)
Equivalent voltage / current ratio	1.414 ×	At equal impedance, power ratio = (voltage ratio)²

Engineering notes

Power quantities use a factor of 10: dB = 10·log10(P2/P1); voltage / current quantities (equal impedance) use a factor of 20: dB = 20·log10(V2/V1).
Rules of thumb: power +3 dB ≈ ×2, +10 dB = ×10; voltage / current +6 dB ≈ ×2, +20 dB = ×10.
Absolute levels: 0 dBm = 1 mW, 0 dBW = 1 W, 0 dBV = 1 V, 0 dBu = 0.775 V, 0 dBμV = 1 µV.
For a cascaded linear system (amplifiers / attenuators / filters) the total gain is the sum of the stage dB values, i.e. the multiplicative ratios multiply.

FAQ

What is Decibel (dB) Calculator for?: Convert ratios, power and voltage to and from decibels: power ratio ↔ dB, voltage ratio ↔ dB, absolute power (dBm / dBW), voltage level (dBV / dBu / dBμV) and cascaded gain.
What is the formula for Decibel (dB) Calculator?: Core formula: dB = 10·log10(P2/P1) = 20·log10(V2/V1) | dBm = 10·log10(P/1mW). The tool returns results instantly using this formula and the selected parameters.
What engineering notes should I keep in mind when using Decibel (dB) Calculator?: Power quantities use a factor of 10: dB = 10·log10(P2/P1); voltage / current quantities (equal impedance) use a factor of 20: dB = 20·log10(V2/V1). Rules of thumb: power +3 dB ≈ ×2, +10 dB = ×10; voltage / current +6 dB ≈ ×2, +20 dB = ×10. Absolute levels: 0 dBm = 1 mW, 0 dBW = 1 W, 0 dBV = 1 V, 0 dBu = 0.775 V, 0 dBμV = 1 µV. For a cascaded linear system (amplifiers / attenuators / filters) the total gain is the sum of the stage dB values, i.e. the multiplicative ratios mul…