What is the dBm to mW Calculator?
The dBm to mW calculator converts a power level expressed in decibel-milliwatts (dBm) into linear power in milliwatts (mW). dBm is a logarithmic unit widely used in radio frequency (RF), microwave, fiber-optic, and telecommunications engineering because it lets engineers express a huge range of power levels with small, easy-to-handle numbers. This tool is universal — it applies anywhere RF or signal power is measured, regardless of country.
How to use it
Enter the power level in dBm (it can be positive, negative, or zero) and the calculator instantly returns the equivalent power in milliwatts and watts. A value of 0 dBm always equals exactly 1 mW, which is the reference point of the dBm scale.
The formula explained
The conversion is based on the definition of the decibel relative to 1 milliwatt:
$$P_{\text{mW}} = 10^{\left(\frac{\text{dBm}}{10}\right)}$$
Because the scale is logarithmic, every increase of 10 dBm multiplies the power by 10, and every 3 dBm roughly doubles it. The inverse conversion is \(\text{dBm} = 10 \cdot \log_{10}(\text{mW})\). To get watts, the result is simply divided by 1000.
Worked example
Suppose a transmitter outputs 30 dBm. Then $$\text{mW} = 10^{\left(\frac{30}{10}\right)} = 10^3 = 1000 \text{ mW},$$ which equals 1 watt. A reading of -20 dBm gives $$10^{\left(\frac{-20}{10}\right)} = 10^{-2} = 0.01 \text{ mW},$$ a typical low-level received signal.
FAQ
What is 0 dBm in mW? Exactly 1 mW — dBm is defined relative to one milliwatt.
Can dBm be negative? Yes. Negative dBm values represent powers below 1 mW, common for received signals in wireless systems.
How do I convert mW back to dBm? Use \(\text{dBm} = 10 \cdot \log_{10}(\text{mW})\). For example, \(100 \text{ mW} = 10 \cdot \log_{10}(100) = 20 \text{ dBm}\).
