Convert RF and audio power between dBm, dBW, watts and milliwatts in either direction. Add an impedance to also get the RMS voltage, and check the 1 dB step table around your value.
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Ω
50 Ω for RF, 75 Ω for TV/video, 600 Ω for audio. Leave empty to skip.
Enter your values to see the result.
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How to use the dBm to Watts
Enter the value you want to convert.
Choose the unit it is in: dBm, dBW, W, mW, µW, nW or dBµV.
Optionally set an impedance (50 Ω for most RF gear) to see the matching voltage.
Read the result in every unit with the formula steps.
Use the tables to see what each extra dB means, or copy the results.
dBm and watts formulas
Convert
Formula
Example
dBm → watts
P = 10^((dBm − 30) ÷ 10)
27 dBm → 0.501 W
dBm → milliwatts
P(mW) = 10^(dBm ÷ 10)
13 dBm → 19.95 mW
watts → dBm
dBm = 10 × log10(P × 1000)
5 W → 36.99 dBm
dBW ↔ dBm
dBm = dBW + 30
10 dBW → 40 dBm
dBm → volts (R ohms)
V(RMS) = √(10^((dBm − 30) ÷ 10) × R)
0 dBm, 50 Ω → 0.2236 V
A decibel value is always a ratio. dBm compares a power with 1 milliwatt, so 0 dBm means exactly 1 mW. Adding decibels multiplies power: +10 dB is ×10, +20 dB is ×100 and +3 dB is almost exactly ×2. That is why dBm is convenient for radio links: you can add amplifier gains and subtract cable and path losses instead of multiplying.
Common dBm values
dBm
Power
Typical example
+60 dBm
1 kW
High-power broadcast transmitter output
+50 dBm
100 W
HF amateur radio transceiver
+37 dBm
5 W
Handheld VHF/UHF radio (high power)
+30 dBm
1 W
Reference point: one watt
+20 dBm
100 mW
Typical 2.4 GHz Wi-Fi access point
+10 dBm
10 mW
Low-power IoT or short-range radio transmitter
0 dBm
1 mW
Reference point: one milliwatt
−30 dBm
1 µW
Very strong received signal close to a transmitter
−60 dBm
1 nW
Good Wi-Fi signal at the receiver
−90 dBm
1 pW
Weak, barely usable mobile or Wi-Fi signal
−174 dBm/Hz
4 × 10⁻²¹ W per Hz
Thermal noise floor at room temperature
Frequently asked questions
How do I convert dBm to watts?
Use P(W) = 10^((dBm − 30) ÷ 10). For example 20 dBm = 10^(−1) = 0.1 W (100 mW), and 30 dBm = 10^0 = 1 W.
How do I convert watts to dBm?
Use dBm = 10 × log10(P in watts × 1000), or equivalently dBm = 10 × log10(P in mW). 1 W is 30 dBm, 100 mW is 20 dBm and 1 mW is 0 dBm.
What is the difference between dBm and dBW?
dBm is referenced to 1 milliwatt and dBW to 1 watt. Because 1 W = 1000 mW, which is 30 dB, dBm = dBW + 30. So 0 dBW = 30 dBm = 1 W.
What does +3 dB or +10 dB mean in power?
Each +3 dB roughly doubles the power (×1.995) and each +10 dB multiplies it by exactly 10. −3 dB is about half the power and −10 dB is one tenth.
Can dBm be negative?
Yes. Any power below 1 mW is negative in dBm. A received Wi-Fi signal of −60 dBm is one nanowatt (10^−9 W), and −90 dBm is one picowatt.
How do I convert dBm to volts?
First convert to watts, then V(RMS) = √(P × R). Across a 50 Ω load, 0 dBm is about 0.2236 V RMS and +10 dBm is about 0.7071 V RMS.
Why can't I convert 0 watts to dBm?
Decibels are logarithmic, and the logarithm of zero is minus infinity. Any real power above zero has a dBm value, however small.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.