dBm to Watts Converter
Enter a single power level in dBm, watts or milliwatts and read the matching value in the other two units. The calculator uses the standard log10 conversion and shows all three results side by side, so it fits transmitter output, receiver sensitivity, link budgets and antenna gain math. dBm may be zero or negative, while watts and milliwatts must be greater than zero.
How to use the dBm to watts calculator
- Open the 'I have' menu and pick the unit you already know: dBm, Watts or Milliwatts.
- Type the power value into the number box, for example 30.
- Read the three result cards for dBm, Watts and Milliwatts, each rounded to four decimals.
- Click the copy button to grab all three lines at once.
- Switch the unit or edit the value to convert a different figure right away.
Examples
30 dBm (a 1 watt handheld radio) to watts
I have: dBm, value: 30
30 dBm, 1 W, 1000 mW
100 watts to dBm
I have: Watts, value: 100
50 dBm, 100 W, 100000 mW
A weak -10 dBm signal to watts
I have: dBm, value: -10
-10 dBm, 0.0001 W, 0.1 mW
Frequently asked questions
What is the dBm to watts formula?
Power in milliwatts is 10 raised to the dBm divided by 10, so mW = 10^(dBm / 10). Divide milliwatts by 1000 to get watts. For example 30 dBm is 1000 mW, which is exactly 1 watt.
How do I convert watts to dBm?
First convert watts to milliwatts by multiplying by 1000, then take dBm = 10 * log10(milliwatts). So 100 watts is 100000 mW, which is 50 dBm.
What is 0 dBm in watts?
0 dBm equals 1 milliwatt, which is 0.001 watts. The dBm scale is referenced to 1 milliwatt, so 0 dBm is exactly that reference power and everything below it lands in negative dBm.
Can I enter a negative dBm value?
Yes. Negative dBm is fully supported and represents power below 1 milliwatt, which is normal for received signals. A sensitive receiver might report -90 dBm, so small numbers here are expected rather than errors.
Why can't I enter zero or negative watts and milliwatts?
Watts and milliwatts are linear power values, and the tool must take log10 of them to produce dBm. The logarithm of zero or a negative number is undefined, so those units are limited to values greater than zero. Only dBm accepts zero or negative input.
How is the result rounded?
Each displayed value is rounded to four decimal places. Very small received powers can therefore show as 0 in the watts card even though the underlying milliwatt figure is still tiny but nonzero.
Why does adding 3 dB roughly double the power?
Because the scale is logarithmic, every 3 dB increase is close to a factor of two in power, and every 10 dB is exactly a factor of ten. So 33 dBm is about twice the power of 30 dBm, and 40 dBm is ten times it.
Is dBm the same as dBW?
No. dBm is referenced to 1 milliwatt while dBW is referenced to 1 watt, so they differ by exactly 30. To convert, subtract 30 from dBm to get dBW. This tool works in dBm, watts and milliwatts only.
Does anything get sent to a server?
No. The conversion runs entirely in your browser with plain arithmetic, so nothing about the values you type is uploaded or stored.
Learn more
- What dBm means and how it relates to watts
A plain guide to the decibel-milliwatt scale, why RF engineers prefer it, and how to move between dBm, milliwatts and watts by hand.
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