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dB

Decibel converter: dBm, mW, W, dBW and dB ratios

Our decibel converter links absolute power (dBm, dBW, W, mW, uW) and dB ratios on one surface. Power uses 10 log10, voltage uses 20 log10 (because P is proportional to V squared). Landmarks: 0 dBm = 1 mW, +30 dBm = 1 W, +3 dB doubles power.

Inputs
Conversion type
Starting value

Used for dBµV + RMS voltage (absolute power) and the voltage/power crossing.

Compares the entered power against the standard's limit. Indicative: real conformity also depends on antenna gain, duty cycle and the channel plan.

P 10log 0 x1 3 x2 10 x10 20 x100 V 20log 0 x1 6 x2 20 x10 40 x100 dB (top) -> ratio (bottom)

dB to ratio: power 10 log, voltage 20 log

Result

0 dBm

Breakdown

dBW -30 dBW
Power 1 mW (1 mW)
dBµV @50Ω 107 dBµV
V RMS @50Ω 223.6 mV

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You receive the result with its direct link. Our design house gets a copy and can react to it, simply reply if you want an engineer's eye on it.

Base-10 decibels. 0 dBm = 1 mW. Power ratios use 10 log, voltage ratios 20 log; a voltage-to-power crossing needs the reference impedance.

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Frequently asked questions

FAQ

What is the maximum RED power at 2.4 GHz?
EN 300 328 caps wideband modulations such as OFDM at 20 dBm EIRP (100 mW), but the 10 dBm/MHz density limit brings DSSS/CCK down to 18 dBm. A 20 dBm module is therefore compliant on OFDM and over the limit on DSSS. The verdict selector compares the entered value against those ceilings, and against EN 300 220 (868 MHz, 25 mW e.r.p.), EN 301 893 (5 GHz) and FCC 15.247. The verdict is indicative: real conformity also depends on antenna gain, duty cycle and the channel plan.
Why does power use 10 log and voltage use 20 log?
Because power is proportional to voltage squared at equal impedance (P = V squared / Z). A voltage ratio r therefore gives a power ratio r squared, and 10 log10(r squared) = 20 log10(r). The factor 20 is not a separate rule, it is the factor 10 applied to a quadratic quantity. Reference: IEC 60027-3.
What is the difference between dBm and dBW?
dBm references 1 milliwatt, dBW references 1 watt. Since 1 W = 1000 mW and 10 log10(1000) = 30, you always have dBm = dBW + 30. So 0 dBm = -30 dBW = 1 mW, and +30 dBm = 0 dBW = 1 W. Our tool shows both references plus the linear values (W, mW, uW) side by side.
What do the +3 dB, +6 dB and -3 dB landmarks mean?
+3 dB is a doubling of power (exactly +3.01 dB for x2). +6 dB is a doubling of voltage (exactly +6.02 dB), which is also x4 in power. -3 dB is half power, the -3 dB point that defines a filter bandwidth. These landmarks let you sanity-check a calculation in your head before trusting the tool.
Why is a reference impedance needed to go from voltage to power?
A voltage alone does not define a power: you need P = V squared / Z. Without an impedance, the voltage to absolute power crossing is undefined. We offer 50 ohm (RF, default), 75 ohm (video, antenna) and 600 ohm (audio). For a pure ratio at one constant impedance, Z cancels out and is not required.
Why is a ratio of 0 or negative rejected?
The base-10 logarithm is only defined for strictly positive values. A ratio of 0 would return minus infinity, and a negative ratio has no physical meaning for a power or an amplitude. The tool therefore requires a ratio greater than zero and returns a message rather than a NaN or infinite result, keeping every conversion usable.
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AESTECHNO is an electronics design office near Montpellier, France, with 10+ years of experience in RF, IoT and embedded design, and a 100% first-pass rate on CE/FCC certification.