All about dB...or is it Db, db...

dBm - dBw Watts conversion chart

- chart or table to provide a conversion between power measured in dBm or dBW and power measured in watts. dBm and dBW are widely used in conjunction with RF test equipment including spectrum analyzers and signal generators.
 

The decibel is widely used in radio and electronics design calculations in particular it is used in many RF or radio frequency associated specifications and details. When measuring radio frequency, or RF power, it is often easier to have a measurement made in a way that it is easy to compare the two levels. As a result many power levels are specified in dBm or dBW, and much RF test equipment including power meters, spectrum analysers, signal generators and the like have calibrations in dBm or dBW. Often RF components such as mixers, oscillators and the like, as well as the interfaces between modules in RF equipment have their levels specified in dBm or dBW. Radio transmitters may also have their output levels expressed in this way.

 

What are dBm and dBW?

In itself a decibel is not an absolute level. It is purely a comparison between two levels, and on its own it cannot be used to measure an absolute level. As a result of this the quantities of dBm and dBW are used:

  • dBm - This is a power expressed in decibels relative to one milliwatt.
  • dBW - This is a power expressed in decibels relative to one watt.

From this it can be seen that a level of 10 dBm is ten dB above one milliwatt, i.e. 10 mW. Similarly a power level of 20 dBW is 100 times that of one watt, i.e. 100 watts.

A more extensive conversion table of dBm, dBW and power is given below:


 
DBM DBW WATTS TERMINOLOGY
+100 +70 10 000 000         10 Megawatts
+90 +60 1 000 000         1 Megawatt
+80 +50 100 000         100 kilowatts
+70 +40 10 000         10 kilowatts
+60 +30 1 000         1 kilowatt
+50 +20 100         100 watts
+40 +10 10         10 watts
+30 0 1         1 watt
+20 -10 0.1         100 milliwatts
+10 -20 0.01         10 milliwatts
0 -30 0.001         1 milliwatt
-10 -40 0.0001         100 microwatts
-20 -50 0.00001         10 microwatts
-30 -60 0.000001         1 microwatt
-40 -70 0.0000001         100 nanowatts
-50 -80 0.00000001         10 nanowatts
-60 -90 0.000000001         1 nanowatt

 

The use of the values dBm and dBW is widespread. They are found as direct calibration scales on many items of RF test equipment often being used in preference to the more elementary basic units of watts or milliwatts. Items of RF test equipment including power meters, signal generators and RF spectrum analyzers in particular use these units. Accordingly to be able to understand the RF test equipment specifications it is necessary to have an understanding of dBm and dBW. Also many RF components are also specified in terms of dBm or dBW.

  

Table of decibel values

- a table or chart of deciBels against Power and Voltage or Current Ratios.
 

The decibel is widely used in radio and electronics design calculations. When undertaking electronics or RF design and development it is often necessary to compare the value of two parameters. It is then possible to alter the electronics design to match the requirements. As values in electronics circuits may vary quite widely, it is often convenient to use a logarithmic scale such as the decibel (dB).
 

DECIBELS (DB) POWER RATIO CURRENT OR VOLTAGE RATIO
0.1 1.023 1.012
0.2 1.047 1.023
0.3 1.072 1.035
0.4 1.096 1.047
0.5 1.122 1.059
0.6 1.148 1.072
0.7 1.175 1.084
0.8 1.202 1.096
0.9 1.230 1.109
1.0 1.259 1.122
2.0 1.585 1.259
3.0 1.995 1.413
4.0 2.512 1.585
5.0 3.162 1.778
6.0 3.981 1.995
7.0 5.012 2.239
8.0 6.310 2.512
9.0 7.943 2.818
10 10.0 3.162
20 102 10.0
30 103 31.62
40 102 100.0
50 105 316.2
60 106 1000.0
70 107 3162.3
80 108 10000
90 109 31623
10 1010 100000

 

 

dBm & Voltage Conversion Table

- conversion table to convert between dBm, Watts and voltage in a 50 ohm system.
 

When working with RF power, it is often useful to know the voltage level for a given power.

The table below provides a chart to convert between dBm, watts and voltage - peak to peak in a 50Ω system.

Although voltage levels are unlikely to rise to significant levels which might cause damage for power levels measured in dBm, the voltages are often used in other calculations.

Three tables have been included. These have been chosen because the voltages move from readings measured in millivolts to those in volts. Also as the milliwatts change to watts, the change in the table is made.

 

dBm / millivolts / milliWatts conversion table

This conversion table charts the values for dBm against milliwatts and the relevant voltage expressed in millivolts.

It is applicable to many lower power applications.
 

DBM MILLIWATTS VOLTAGE
MILLIVOLTS (P-P)
VOLTAGE
MILLIVOLTS (RMS)
-30 0.0010 20 7.1
-28 0.0016 25.2 8.9
-26 0.0025 31.7 11.2
-24 0.0040 40.0 14.2
-22 0.0063 50.2 17.8
-20 0.010 63.2 22.4
-18 0.016 79.6 28.2
-16 0.025 100 35.5
-14 0.040 126 44.7
-12 0.063 159 56.4
-10 0.100 200 71.0
-8 0.16 252 89.4
-6 0.25 317 112
-4 0.40 399 142
-2 0.63 502 178
0 1.00 632 224
2 1.58 796 282
4 2.51 4000 1420


 

 

dBm - milliwatts - Volts conversion table

This conversion table charts the values for dBm against milliwatts and the relevant voltage expressed in volts.

It is applicable to many medium power applications.

 
DBM MILLIWATTS VOLTAGE
VOLTS (P-P)
VOLTAGE
VOLTS (RMS)
0 1.00 0.632 0.224
2 1.58 0.796 282
4 2.51 4.00 1.42
6 3.98 1.26 0.45
8 6.31 1.59 0.56
10 10 2.00 0.71
12 15.8 2.52 0.89
14 25.1 3.17 1.12
16 39.8 3.99 1.41
18 63.1 5.02 1.78
20 100 6.32 2.24
22 158 7.95 2.82
24 25.1 10.0 3.55
26 398 12.6 4.48
28 631 15.9 5.64
30 1000 20.0 7.10
32 1585 25.2 8.94
34 2510 31.7 11.2

 

dBm - Watts - Volts conversion table

This conversion table charts the values for dBm against milliwatts and the relevant voltage expressed in volts.

It is applicable to many high power applications.
 

DBM VOLTAGE
MV (P-P)
WATTS
30 1.00 20 7.10
32 1.58 25.2 8.94
34 2.51 31.7 11.3
36 3.98 40.0 14.1
38 6.31 50.2 17.8
40 10.0 63.2 22.4
42 15.9 79.6 28.2
44 25.1 100 35.5
46 39.8 126 44.7
48 63.1 159 56.4
50 100 200 71.0
52 159 252 89.4
54 251 317 112
56 398 399 142
58 631 502 178
60 1000 632 224
62 1585 796 282