RF Power and Voltage

The RF Power and Voltage calculator relates radio-frequency (RF) power, power level in dBm, and voltage for a specific impedance. The dBm is a logarithmic unit of power, used in radio and microwave electronics.  It is the power ratio measured in decibels (dB) with a reference power of 1 mW = 0.001 W.  

• RF Power from dBm
• dBm from RF Power
• Voltage from dBm
• Voltage from RF Power
• dBm from Voltage and Impedance
• RF Power from Voltage and Impedance

Power & Voltage

Power is typically measured in watts (W) or mW in electronics.  For a voltage (V) applied across an impedance (Z), the power is given by

`P = V^2/Z`.

Power level (dBm)

The power level in dBm is an absolute measure of power, because it uses the reference power `P_0` = 0.001 W.  In contrast, decibels (dB) are a dimensionless logarithmic ratio of two powers:

`dB = 10 log_10(P_2/P_1)`.

Along similar lines,

`dBm = 10 log_10(P/P_0)`.

Examples

• 1 W is `10 log_10((1W)/(0.001W)) = 10 log_10(1000) = 10*3 = 30 dBm`.  
• 1 mW is `10 log_10((0.001W)/(0.001W)) = 10 log_10(1) = 10*0 = 0 dBm`.  
• 2 mW is `10 log_10((0.002W)/(0.001W)) = 10 log_10(2000) = 10*0.301 = 3.01 dBm`.  
• 1 `mu`W is `10 log_10((0.000001W)/(0.001W)) = 10 log_10(0.001) = 10*(-3) = -30 dBm`.  

Rules of Thumb

• Every increase/decrease of 1 dBm corresponds to a power increase/decrease of a factor of approximately 1.25.
• Every increase/decrease of 3 dBm corresponds to a power increase/decrease of a factor of approximately 2.
• Every increase/decrease of 10 dBm corresponds to a power increase/decrease of a factor of 10.