How to convert watts to dBm
RF Power Unit Converter
Convert between Watts and dBm (decibel-milliwatts)
Conversion Results
About RF Power Units
What is dBm?
dBm (decibel-milliwatts) is a unit of power expressed in decibels relative to one milliwatt. It's commonly used in radio, microwave, and fiber optic networks to express signal strength and power levels.
Conversion Formula
Watts to dBm: dBm = 10 × log10(Pwatts × 1000)
dBm to Watts: Pwatts = 10(dBm/10) ÷ 1000
Common Reference Values
Note: Every +3 dBm represents approximately doubling of power, while every -3 dBm represents approximately halving of power. A 10 dBm increase means the power is 10 times greater.
The power P(dBm) in dBm is equal to 10 times the base 10 logarithm of 1000 times the power P(W) in watts (W) divided by 1 watt (W):
P(dBm) = 10 ⋅ log10( 1000 ⋅ P(W) / 1W) = 10 ⋅ log10( P(W) / 1W) + 30
so
1W = 30dBm
Example
Convert 20 watts to dBm:
P(dBm) = 10 ⋅ log10(1000⋅20W) = 43.0103dBm
Watt to dBm conversion table
| Power (W) | Power (dBm) |
|---|---|
| 0 W | not defined |
| 0+ W | -∞ dBm |
| 0.00001 W | -20 dBm |
| 0.0001 W | -10 dBm |
| 0.001 W | 0 dBm |
| 0.01 W | 10 dBm |
| 0.1 W | 20 dBm |
| 1 W | 30 dBm |
| 10 W | 40 dBm |
| 100 W | 50 dBm |
| 1000 W | 60 dBm |
| 10000 W | 70 dBm |
| 100000 W | 80 dBm |
| 1000000 W | 90 dBm |
