What “nanoscale” means, and why the 1–100 nm range is a convention

How it works

The NNI describes nanotechnology as understanding and control of matter at roughly 1–100 nm, where matter can behave differently from the same substance in bulk. NIOSH reports the same range from ISO/TS 27687:2008, which defines a nano-object by how many of its external dimensions fall in it. EPA treats many such materials as ordinary chemical substances under TSCA that may nevertheless behave differently at that scale. The three agree on the number and differ in purpose: describing a research field, scoping worker protection, and deciding what has to be reported. A material at 120 nm is not exempt from the physics; it is outside a definition.

A concrete case

A pigment supplier states that its particles are “nano-free” because the median diameter is 180 nm. A median says nothing about the tail of the distribution. The question worth asking is what fraction of particles falls below 100 nm and by which measurement method, not whether one summary number clears the line.

Questions worth asking

• Ask which dimension is being described: a diameter, a layer thickness, a pore size or a feature pitch.
• Ask for the size distribution and the measurement method, not only a median or a nominal value.
• Ask whether the material was engineered to that size or simply happens to contain a fraction of it.

Sources

• National Nanotechnology Initiative — About Nanotechnology ↗

  The NNI describes nanotechnology as understanding and control of matter at dimensions of approximately 1 to 100 nanometres, and states that matter can show physical, chemical and biological properties at that scale that differ from bulk material, single atoms and molecules.

  Boundary: A programme definition and orientation page. It does not establish any particular material’s properties, performance or safety.

  Locator, anchor and reuse basis

  Read at: About Nanotechnology, opening paragraph; “How small is nano?”. Inspected 2026-09-19. Original paraphrase and link only; no government text reproduced beyond short attributed wording.

  Verify by searching the source for: dimensions between approximately 1 and 100 nanometers. If that phrase is not there, or does not carry the meaning stated above, this citation is wrong and we want to know.

• NIOSH — Approaches to Safe Nanotechnology: Managing the Health and Safety Concerns Associated with Engineered Nanomaterials (DHHS/NIOSH 2009-125) ↗

  NIOSH reports the ISO/TS 27687:2008 definition of a nano-object as material with one, two or three external dimensions in the range of approximately 1–100 nm, with nanoplate, nanofibre (nanotube hollow, nanorod solid) and nanoparticle as the subcategories by how many dimensions are nanoscale; it distinguishes engineered nanoparticles from incidental ultrafine particles while noting it is unclear whether that source-based distinction is justified for safety purposes; and it states that limits set for larger particles of similar chemical composition may not be health-protective at the nanoscale — its example being that the OSHA permissible exposure limit for graphite may not be a safe limit for carbon nanotubes — and that nanoparticles may be more biologically reactive than larger particles of similar composition.

  Boundary: Guidance for managing workplace risk, not a toxicological finding about any specific material and not a regulation, and reading it does not substitute for qualified occupational-health practice. Critically, it is a 2009 document: its statement that no specific US exposure limits then existed for airborne engineered nanomaterials describes 2009 and has since been overtaken by NIOSH’s own recommended exposure limits for titanium dioxide (2011) and carbon nanotubes and nanofibres (2013). This section cites it only for the definitions and the size-versus-composition reasoning, never for the current state of exposure limits.

  Locator, anchor and reuse basis

  Read at: §4.1 Nano-objects and §4.2 Ultrafine Particles, p. 8; §8.3.5 Respirators, pp. 43–44. Inspected 2026-09-20. Public-domain federal document; paraphrased with short attributed wording and linked, not reproduced.

  Verify by searching the source for: one, two, or three external dimensions in the size range from approximately 1–100 nm. If that phrase is not there, or does not carry the meaning stated above, this citation is wrong and we want to know.

• EPA — Control of Nanoscale Materials under the Toxic Substances Control Act ↗

  EPA treats many nanoscale materials as chemical substances under TSCA, notes that the same substance at the nanoscale may behave differently, and describes a regulatory approach that includes an information-gathering reporting rule and premanufacture notification for new nanoscale materials.

  Boundary: Reporting or review under TSCA is a regulatory process, not a finding that a material is safe, effective or approved for a use.

  Locator, anchor and reuse basis

  Read at: Nanoscale Materials; Regulatory Approach; Information gathering rule; Reporting under the rule. Inspected 2026-09-19. Original paraphrase and link only.

  Verify by searching the source for: regarded as “chemical substances” under the Toxic Substances Control Act. If that phrase is not there, or does not carry the meaning stated above, this citation is wrong and we want to know.

Continue

• Why the same material behaves differently when it is small
• Every characterisation method measures its own quantity
• Regulatory status is not a safety finding, and medical claims have their own bar