# Electric field strength

> Volts per metre, reported both for power-frequency electric fields near wiring and for radiofrequency fields near transmitters.

- Canonical URL: https://emfbase.com/quantities/electric-field-strength
- Collection: Quantities & units
- Record id: `quantities:electric-field-strength`
- Status: verified
- Last verified: 2026-08-12
- JSON: https://emfbase.com/api/quantities/electric-field-strength
- Also known as: E field, V/m, volts per meter

## Key values

- **Symbol:** E
- **SI unit:** V/m
- **Units in use:** kV/m, V/m, mV/m, µV/m

## 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

- `nist-si` National Institute of Standards and Technology. *The International System of Units (SI), NIST Special Publication 330*. https://www.nist.gov/pml/special-publication-330 — government, link checked 2026-08-12
- `itu-fs-relations` International Telecommunication Union. *Free-space path loss and power density relations (ITU-R P.525)*. https://www.itu.int/rec/R-REC-P.525/en — standard, link checked 2026-08-12
- `fcc-1310` U.S. Government Publishing Office (eCFR). *47 CFR § 1.1310 — Radiofrequency radiation exposure limits*. https://www.ecfr.gov/current/title-47/section-1.1310 — regulation, link checked 2026-08-12

Data licence: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Dataset version 2026.08.1. Retrieved from EMFBase, https://emfbase.com.

This record is reference data, not medical or legal advice. Regulatory limits, scientific guidelines and precautionary values are labelled separately and answer different questions.