Enter the dBm and the load impedance/resistance (ohms) into the calculator to determine the RMS current. (For a purely resistive load, impedance and resistance are the same quantity; you can use either field.)

dBm to Current Calculator

Enter any 2 of: dBm, load impedance/resistance, and current to calculate the missing value. (Impedance and Resistance represent the same load; enter one or enter matching values.)





Current from dBm Formula

The following formula is used to calculate RMS current from a dBm power level into a (purely resistive) load impedance.

I_{\mathrm{rms}}=\sqrt{\frac{10^{(dBm-30)/10}}{Z}}
  • Where I is the RMS current (amps)
  • dBm is the power level in dBm (referenced to 1 mW)
  • Z is the load impedance (ohms). For a purely resistive load, Z = R.
  • R is the load resistance (ohms) (used when the load is purely resistive)

How to Calculate Current from dBm?

The following example problems outline how to calculate RMS current from dBm.

Example Problem #1

  1. First, determine the dBm. In this example, the dBm is determined to be 14.
  2. Next, determine the load impedance (ohms). For this problem, the load impedance is 5000 Ω.
  3. For a purely resistive load, the resistance equals the impedance. In this case, R = 5000 Ω.
  4. Finally, calculate the RMS current from dBm using the formula above.

I = √(10^((dBm − 30)/10) / Z)

Inserting the values from above and solving yields:

I = √(10^((14 − 30)/10) / 5000) = 0.00224 (amps)

Example Problem #2

Using the same method as above, determine the variables required by the formula. For this example problem, these are:

dBm = 42

load impedance (ohms) = 10,000

load resistance (ohms) = 10,000

Enter these given values into the calculator above yields:

I = √(10^((dBm − 30)/10) / Z) = √(10^((42 − 30)/10) / 10,000) = 0.03981 (amps)