# Inverse-square law

> In the far field, doubling the distance quarters the power density: the cheapest and most reliable mitigation available.

- Canonical URL: https://emfbase.com/glossary/inverse-square-law
- Collection: Glossary
- Record id: `glossary:inverse-square-law`
- Status: verified
- Last verified: 2026-08-12
- JSON: https://emfbase.com/api/glossary/inverse-square-law

## Key values

- **Category:** physics

## Definition

Power density from a point source falls as 1/d². Three times the distance is nine times less; ten times the distance is a hundred times less. This is why moving a router across a room outperforms most shielding purchases. Two caveats: it does not apply in the near field, and it does not apply to fields from extended sources such as a long transmission line, where fall-off is closer to 1/d.

## Sources

- `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

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.