dBm to Watts & Decibel-Milliwatts RF Power Calculator

Decibel-Milliwatts (dBm), RF Power Conversion & Impedance Voltage

The decibel-milliwatt (dBm) is an absolute logarithmic unit of electrical power referenced to 1.0 milliwatt:

• **

• Universal dBm Conversion Formulas**:

P_dBm = 10 _10(P_mW1 mW) = 10 _10(P_Watts) + 30

P_mW = 10^P_dBm10, P_Watts = P_mW1000 = 10^P_dBm - 3010

P_dBW = P_dBm - 30

• **

• RF Voltage Across Characteristic Impedance (Z_0)**:

V_RMS = √(P_Watts) × Z_0 = √(P_mW)1000 × Z_0

V_p-p = 2√(2) × V_RMS ≈ 2.8284 × V_RMS

• **

• The RF 3-dB and 10-dB Rules of Thumb**:

• +3 dBm: Doubles linear power (2×)

• -3 dBm: Halves linear power (0.5×)

• +10 dBm: Multiplies linear power by 10×

• -10 dBm: Reduces linear power by 10× (0.1×)

• **

• Standard Telecom & Wireless Power Benchmarks**:

• -100 dBm: 0.1 pW Weak GPS satellite signal at Earth surface

• -70 dBm: 100 pW Strong, fast Wi-Fi connection

• 0 dBm: 1.0 mW Reference baseline (0.224 V_RMS @ 50Ω)

• 4 dBm: 2.5 mW Bluetooth Class 2 (10m range)

• 20 dBm: 100 mW Standard Wi-Fi router transmit

• 23 dBm: 200 mW Maximum 4G LTE/5G smartphone uplink

• 30 dBm: 1.0 Watt Maximum legal unlicensed FCC ISM band Tx

How to Use This Calculator

Enter your Power Magnitude Value (e.g. 20 in power), Source Power Unit — choose from Decibel-Milliwatts (dBm - Reference 1 mW), Milliwatts (mW), Watts (W), RF Characteristic Impedance (Z₀ in Ohms) (e.g. 50 for RF / 75 for CATV in Ω), and Telecommunications & RF Benchmark — choose from Custom Power & Impedance, 0 dBm Reference (1.0 mW = 0.001 W) → VRMS = 0.2236 V @ 50Ω, Bluetooth Class 2 Device (4.0 dBm = 2.51 mW). Measure twice before entering dimensions — small measurement errors scale up significantly in material estimates.

The Formula

Calculate RF Voltage across Z0: P = V^2 / Z0 -> V_rms = sqrt(P_watts * Z0)

Worked Example

An RF engineer designing a 5G base station link calculates that an antenna transmitting 23 dBm (200 mW) through a 50 Ω coaxial line generates 3.16 V RMS, verifying signal levels are within transceiver linearity specs.

Understanding Your Result

Construction estimates are starting points — site conditions, material specifications, and local code requirements will affect final quantities and costs. Always obtain at least three contractor bids for major projects. Local building departments can confirm permit requirements and inspection milestones. Add waste factors appropriate to the material type and complexity: 10% for simple rectangular shapes, 15–20% for complex geometries or custom cuts.