If you're new to RF and things like signal strength measurements (dB, dBm, RSSI, etc.), the following whitepaper may be helpful: Converting Signal Strength Percentage to dBm Values
Decibals (dB) are used to indicate the ratio of one power level to another. An increase of 3dB doubles the power, so 6dB is equal to 4x the power, 9dB is equal to 8x, etc.
The specific formula is: dB = 10 * log(P1/P2), meaning that for a 4 times difference in power we get:
dB = 10 * log(4/1)
dB = 10 * 0.602
dB = 6.02
The following table shows some key values comparing decibels (dB) and their equivalent increase/decrease factor:
| dB | Increase Factor | Decrease Factor |
| 0 dB | 1x | 1x |
| 1 dB | 1.25x | 0.8x |
| 3 dB | 2x | 0.5x |
| 6 dB | 4x | 0.25x |
| 10 dB | 10x | 0.10x |
| 12 dB | 16x | 0.06x |
| 20 dB | 100x | 0.01x |
dBm is used to indicate transmit and receive sensitivity in milliwatts, and is the power ratio in decibels (dB) of the measured power referenced to one milliwatt (the m in dBm). 0dBm is equal to 1 milliwatt. The following two formulas govern the relationship between dBm and mW:
To convert dBm to mW: P(mW) = 10[P(dBm)/10]
To convert mW to dBm: P(dBm) = log[P(mW)] * 10
For example, if we start with 13dBm, we get the following equivalent value in milliwatts:
mw = 10^[13/10]
mw = 10^1.3
mw = 19.953 (or roughly 20mW)
We can also convert 20 mW back to dBm as follows:
dBm = log[20] * 10
dBm = 1.301 * 10
dBm = 13.01
Some common value can be seen in the table below:
| dBm Increase | mW | dBm Decrease | mW |
| 0 dBm | 1 mW | 0 dBm | 1 mW |
| 1 dBm | 1.25 mW | 1 dBm | 0.8 mW |
| 3 dBm | 2 mW | 3 dBm | 0.5 mW |
| 6 dBm | 4 mW | 6 dBm | 0.25 mW |
| 7 dBm | 5 mW | 7 dBm | 0.20 mW |
| 10 dBm | 10 mW | 10 dBm | 0.1 mW |
| 12 dBm | 16 mW | 12 dBm | 0.06 mW |
| 20 dBm | 100 mW | 20 dBm | 0.01 mW |
For more information, feel free to look at the Wikipedia pages for decibels and dBm.