Select RMS current, dBm power level or load resistance to calculate from the other two values. This model uses one positive, purely resistive load in Ω, kΩ or MΩ.

Find current from power level and resistance.

Purely resistive load. Current is RMS; load resistance is the real positive resistance, not complex impedance magnitude.

dBm to Current Formula

The calculator converts dBm to power in watts, then uses the RMS current relationship for a resistive load. Load impedance and load resistance are treated as the same value when the load is purely resistive.

P = 10⁽(dBm - 30) / 10)
Iᵣms = sqrt(P / Z)
P = Iᵣms² × Z
dBm = 10 × log10(P / 0.001)
Z = P / Iᵣms²
  • dBm is power level in decibels referenced to 1 milliwatt.
  • P is power in watts.
  • Irms is RMS current in amperes.
  • Z denotes the purely resistive load in ohms in these formulas; it is not the magnitude of a reactive impedance.
  • R is load resistance in ohms. For this calculator, R and Z represent the same load value.

The calculator has three main functions:

  • Calculate current: select RMS current, then enter dBm and load resistance. The calculator converts dBm to watts, then solves Irms = sqrt(P/Z).
  • Calculate dBm: select Power level (dBm), then enter RMS current and load resistance. The calculator finds power with P = Irms2 * Z, then converts watts to dBm.
  • Calculate load resistance: select Load resistance, then enter dBm and RMS current. The calculator converts dBm to watts, then solves Z = P/Irms2.

Common dBm Power and Current Values

These reference values use a 50 Ω resistive load and RMS current.

dBm Power Current in 50 Ω
-30 dBm 1 μW 0.141 mA
-20 dBm 10 μW 0.447 mA
-10 dBm 100 μW 1.414 mA
0 dBm 1 mW 4.472 mA
10 dBm 10 mW 14.142 mA
20 dBm 100 mW 44.721 mA
30 dBm 1 W 141.421 mA

Examples

Example 1: Find current from dBm and load

You have a signal level of 10 dBm across a 50 Ω load.

P = 10⁽(10 - 30) / 10) = 0.01 W
Iᵣms = sqrt(0.01 / 50) = 0.014142 A

The RMS current is 0.014142 A, or 14.142 mA.

Example 2: Find dBm from current and load

You have 20 mA RMS through a 75 Ω load.

P = 0.020² × 75 = 0.03 W
dBm = 10 × log10(0.03 / 0.001) = 14.77 dBm

The power level is 14.77 dBm.

FAQ

Is the current value RMS or peak current?

The calculator uses RMS current. dBm is a power measurement, and RMS current is the standard current value used with average power in a resistive load. If you have sinusoidal peak current, convert it to RMS first by dividing by sqrt(2).

Are impedance and resistance the same in this calculation?

For this calculator, yes. The redesigned calculator uses one load resistance field instead of duplicate impedance and resistance aliases. This is correct for a purely resistive load. If your load has reactance, the real power calculation can require phase angle or the real part of the impedance.

Why does 0 dBm not mean zero power?

dBm is a logarithmic power unit referenced to 1 milliwatt. A value of 0 dBm means the power is exactly 1 mW, not zero. Negative dBm values are less than 1 mW, and positive dBm values are greater than 1 mW.