# Magnetic flux density

> The quantity an ELF gaussmeter reports, expressed in milligauss or microtesla, used to assess wiring, transformers and power lines. 1 µT = 10 mG.

- Canonical URL: https://emfbase.com/quantities/magnetic-flux-density
- Collection: Quantities & units
- Record id: `quantities:magnetic-flux-density`
- Status: verified
- Last verified: 2026-08-12
- JSON: https://emfbase.com/api/quantities/magnetic-flux-density
- Also known as: B field, magnetic field, gauss, tesla

## Key values

- **Symbol:** B
- **SI unit:** T
- **Units in use:** T, mT, µT, nT, G, mG

## What it measures

Magnetic component of a low-frequency field. Passes through walls and almost all shielding materials, so mitigation is by distance or by fixing the current imbalance that creates it.

## Units

Multiplier to the SI unit (T).

- **T (tesla)** — 1 T = 1 T
- **mT (millitesla)** — 1 mT = 0.001 T
- **µT (microtesla)** — 1 µT = 1 × 10^-6 T
- **nT (nanotesla)** — 1 nT = 1 × 10^-9 T
- **G (gauss)** — 1 G = 0.0001 T
- **mG (milligauss)** — 1 mG = 1 × 10^-7 T

## Relationships to other quantities

- **H (A/m) = B (µT) / 1.25663706** — Magnetic field strength H relates to flux density B by the permeability of free space, µ₀ = 4π × 10⁻⁷ H/m. 1 A/m ≈ 1.2566 µT in air.

## Related records

- [Building Biology SBM-2024 AC magnetic field bands](https://emfbase.com/limits/building-biology-ac-magnetic-bands): Sleeping-area grades at 50/60 Hz: below 0.2 mG no anomaly, 0.2–1 mG weak, 1–5 mG strong, above 5 mG extreme.
- [ICNIRP 2010 general public magnetic field reference level at 50/60 Hz](https://emfbase.com/limits/icnirp-public-magnetic-field-50-60-hz): 200 µT (2000 mG) for the public and 1000 µT occupational — five orders of magnitude above typical household background.

## 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
- `sbm-2024` Institut für Baubiologie + Nachhaltigkeit (IBN) (2024). *Building Biology Evaluation Guidelines for Sleeping Areas (SBM-2024)*. https://buildingbiology.com/site/downloads/SBM-2024_EVALUATION_GUIDELINES_EN.pdf — ngo, 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.