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Power Density Converter

Convert electric field strength to power density (W/m² or mW/cm²) for far-field radiated emissions.

Use this when: You are evaluating RF exposure, antenna effective radiated power, or comparing to SAR and safety limits.

Reference only. Verify against your calibrated setup, antenna calibration data, and the applicable standard before making compliance decisions.

Key formula

S (W/m²) = E² / 377

Example: Enter 377 V/m → 377 W/m²

Valid for far field / plane wave conditions only.

V/m
W/m²
mW/cm²

Field strength to power density

Far-field power density S relates to electric field as S = E² / Z₀. Safety limits, some antenna specs, and RF-exposure discussions are in W/m² or mW/cm² while the EMC plot is in V/m or dBµV/m. This converter does that translation.

It assumes far-field, free-space conditions. Do not use it to invent a SAR number or to replace a site survey.

Frequently asked questions

Quick answers about using this calculator

How do I convert V/m to W/m²?
S (W/m²) = E² / 377 for a plane wave in free space. 1 V/m is about 2.65 mW/m².
Is this an RF-exposure certificate?
No. It is a unit helper. Exposure assessments use defined methods, averaging, and sometimes SAR. Treat the output as a sanity check.

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