dBm to Watts Calculator

Convert logarithmic dBm power to milliwatts and watts, with an ideal RMS voltage for a chosen resistive load.

Power levelNumber from -1000 to 1000 dBm.Load resistanceNumber from 0.000001 to 1000000000 Ω.

Use the units shown beside each field. Decimal and scientific notation are accepted for non-integer fields; blanks, commas, fractions and non-finite entries are rejected.

Calculate

Power0.1 mW

Power0.0001 W

Ideal RMS voltage0.07071067812 V

Ideal RMS current0.001414213562 A

The displayed results apply to the default example. Enable JavaScript to calculate other inputs.

How to use this calculator

1. Replace the example values with measurements or ratings for the exact vehicle, circuit, component or system.
2. Keep every value in the labeled unit and use manufacturer data where available.
3. Select Calculate, then review the result together with the limitations and safety notes.

Formula and method

mW = 10^(dBm/10). W = mW ÷ 1,000. For a resistive load, Vrms = √(P × R) and Irms = P ÷ V.

Calculations run in your browser. Results are hidden whenever an input changes or validation fails, preventing an older result from being mistaken for a new calculation.

Worked example

Power level = -10 dBm; Load resistance = 50 Ω. The calculator returns Power = 0.1 mW; Power = 0.0001 W; Ideal RMS voltage = 0.07071067812 V; Ideal RMS current = 0.001414213562 A.

The worked example uses the same defaults shown in the interface, allowing the formula and displayed result to be checked together.

Limitations and safety

The voltage and current results assume a purely resistive matched load and RMS quantities. RF systems also require impedance, bandwidth, waveform and measurement context.

This is an educational planning model. Confirm ratings, tolerances, code requirements and safe procedures with manufacturers and qualified professionals before purchasing, modifying, wiring or operating equipment.

Frequently asked questions

What does 0 dBm equal?

Zero dBm is exactly 1 milliwatt, or 0.001 watt.

Why does the calculator reject my entry?

Each field shows its supported range. Whole-number fields reject decimals, and all fields reject blanks, words, comma-formatted numbers, fractions and non-finite values.

How should I use the displayed precision?

Keep extra digits while checking the calculation, then round to the precision supported by the measurements, component tolerances and published ratings.

Review notes and reference

Reviewed October 4, 2026. The formula and default example were checked together. The script was tested for defaults, input boundaries, invalid formats, condition-specific errors and recovery after an error. Reference: OSHA electrical safe-work requirements. Explanations and examples are original.

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