, or

(NB dBC is a frequency response weighting & not dBc which is dBs with respect to an RF carrier)

dBWs
The Formula for POWER is 10log POut/1WATT, which gives this easy to
 remember 1dB step table based only on +/- 3, 6 & 10dB. 
Note, dBW is "0" referenced to 1W.

 +3dB is doubling the power, -3dB is only a half.
 +6dB is Quadrupling power, -6dB is only a quarter.
+10dB is 10 fold the power,  -10dB is only a tenth.

mW     dBW       Watts  dBW      Watts  dBW       Watts   dBW      Watts   dBW
10     -20       0.1    -10       1      0        10      10       100      20
12.5   -19       0.125   -9       1.25   1        12.5    11       125      21
15.65  -18       0.1565  -8       1.565  2        15.65   12       156.5    22
20     -17       0.2     -7       2      3        20      13       200      23
25     -16       0.25    -6       2.5    4        25      14       250      24
31.25  -15       0.3125  -5       3.125  5        31.25   15       312.5    25
40     -14       0.4     -4       4      6        40      16       400      26
50     -13       0.5     -3       5      7        50      17       500      27
62.5   -13       0.625   -2       6.25   8        62.5    18       625      28
80     -11       0.8     -1       8      9        80      19       800      29


For Voltage and Currents the formula is 20log in/out, which gives this
easy to remember 2dB step table based only on +/- 6, 12 & 20dB.

 +6dB is doubling the level, -6dB is only a half.
+12dB is Quadroupling level, -12dB is only a quarter.
+20dB is 10 fold the level,  -20dB is only a tenth.

NB +1dB  is about +11% (111%), & -1dB is about -9% (91%) of level. 

Ratio    dB    Ratio   dB     Ratio   dB     Ratio    dB     Ratio   dB
0.01    -40    0.1    -20     1      +0      10      +20     100    +40
0.0125  -38    0.125  -18     1.25   +2      12.5    +22     125    +42
0.01565 -36    0.1565 -16     1.565  +4      15.65   +24     156.5  +44
0.02    -34    0.2    -14     2      +6      20      +26     200    +46
0.025   -32    0.25   -12        2.5    +8        25     +28       250    +48
0.03125 -20      0.3125 -10        3.125 +10        31.25  +30       312.5  +50
0.04    -28      0.4     -8        4     +12        40     +32       400    +52
0.05    -26      0.5     -6        5     +14        50     +34       500    +54
0.0625  -24      0.625   -4        6.25  +16        62.5   +36       625    +56
0.08    -22      0.8     -2        8     +18        80     +38       800    +58

The information contained upon this page is supplied in good faith, and to the best of my knowledge is accurate.
However, I accept no responsibility for damage or injury, however caused, due to the use of this data.
It was originally posted to the Packet radio System by John G8MNY on 24th JAN 2001