W to dBm Calculator

"dBm" is merely a logarithmic expression of a given power level relative to 1 mW. Given by:

Power (dBm) = 10 x Log (Power (w) / 0.001 W)

For example:
1 Watt                 
= 10 x log(1/0.001)
= 10 x log(1000)
= 30 dBm

Rules of Thumb:
1. Adding 3dB = doubling the power. So, 10dBm + 10 dBm = 13 dBm
2. Likewise subtracting 3 dB equals to halving the power
3. Increasing the power by 10 dB equals to increasing the powers by 10 times. i.e. 40 dBm = 10 watts and 50 dBm = 100 watts.