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