Electric field strength

What it measures

Electric component of the field. At power frequency it is easily blocked by grounded conductive surfaces; at radiofrequency it is one of two interchangeable ways to express far-field exposure.

Units

Multiplier to the SI unit (V/m).

kV/m (kilovolt per metre)

1 kV/m = 1,000 V/m

V/m (volt per metre)

1 V/m = 1 V/m

mV/m (millivolt per metre)

1 mV/m = 0.001 V/m

µV/m (microvolt per metre)

1 µV/m = 1 × 10^-6 V/m

Relationships to other quantities

S (W/m²) = E² / 377

Valid in the far field of an antenna, where the wave impedance equals the impedance of free space, 376.73 Ω. Not valid within a wavelength of the source.

dBµV/m = 20 · log₁₀(E in µV/m)

Logarithmic form used by spectrum analysers and EMC test equipment.

Sources

1. nist-si The International System of Units (SI), NIST Special Publication 330 — National Institute of Standards and Technology. government, link checked 2026-08-12.
2. itu-fs-relations Free-space path loss and power density relations (ITU-R P.525) — International Telecommunication Union. standard, link checked 2026-08-12.
3. fcc-1310 47 CFR § 1.1310 — Radiofrequency radiation exposure limits — U.S. Government Publishing Office (eCFR). regulation, link checked 2026-08-12.