In radioengineering it is essential to use the dBs. The dB stands for deci Bell, ie the same as tenth of a Bell.
To convert dB to power-ratio;


To convert ratio to dB;


To do these conversions fast you have to remember some "factors";

1dB=1,25 2dB=1,5 3dB=2 10dB=10 20dB=100 etc.

With these "factors" it is easy to convert, let say 17dB to a ratio. Split 17dB into parts containing the first four factors mentioned above, ie 17=10+3+3+1 this will be 10*2*2*1,25=50 times. (You can also look at it as 20-3, ie half of 100, and after some practice you will most certainly discover several shortcuts!)
When you see a dB-value, you should always ask yourself - "in reference to what?". In RF-technology dB-values are very often used and it is a good idea to get used to this. We not only use dB, we also use dBm, dBW, etc.
When a dB-value is given as dBm then this dB-value is referenced to something, in this case mW. 0dBm is 1mW and therefore 10dBm will be ten times higher, ie 10mW. In the same way will 0dBW be 1W and therefore will 10dBW be equal to 10W.
But why this?
One reason is if you are about to calculate a link budget. A link budget will tell you how much of the transmitted power that will reach the receiver and it will therefore tell you something about the possibility to communicate with the receiving station.