Human Hair Thickness: Diameter in µm, mm, nm & Inches

How thick is a human hair?

There is no one exact diameter for every human hair. Published measurements depend on the person, the individual strand, sampling, and measurement method. One scalp-hair study reported diameters from about 57 to 104 micrometers (µm) in its sample, with an average around 80–83 µm. A Harvard BioNumbers reference lists 60–80 µm as a typical range. These are reference values, not a guarantee for any one strand.

A hair shaft is also not perfectly round at every point, so “width” and “diameter” can vary with how it is measured. Read the scalp-hair study and Harvard BioNumbers’ hair-diameter reference.

Human hair thickness conversion chart

Reference diameter	Millimeters (mm)	Nanometers (nm)	Inches
57 µm	0.057 mm	57,000 nm	0.00224 in
60 µm	0.060 mm	60,000 nm	0.00236 in
80 µm	0.080 mm	80,000 nm	0.00315 in
100 µm	0.100 mm	100,000 nm	0.00394 in
104 µm	0.104 mm	104,000 nm	0.00409 in

In this table, the inch values are rounded conversions from micrometers; the underlying hair measurements remain approximate.

How to convert hair diameter between units

Use these exact metric relationships:

1 µm = 0.001 mm
1 µm = 1,000 nm
1 inch = 25,400 µm

For example, 80 µm × 0.001 = 0.08 mm. To convert micrometers to inches, divide by 25,400: 80 ÷ 25,400 ≈ 0.00315 inches. A micrometer is also called a micron.

Why hair thickness varies

Hair diameter differs between individuals and can vary along a strand. Measurement technique and the location sampled also affect the result. Research on individual hair fibers emphasizes that structure and measurement conditions matter, so a single number should be treated as an example rather than a universal human-hair size. A microscopy study discusses variation and measurement methods.

Frequently asked questions

What is the average diameter of a human hair?

There is no single universal average. The cited scalp-hair study measured a sample averaging about 80–83 µm; Harvard BioNumbers gives a 60–80 µm reference range.

How many microns thick is a hair?

The references cited here place example human-hair measurements in the tens of micrometers. The study sample ranged from about 57 to 104 µm.

How thick is hair in millimeters?

Convert micrometers to millimeters by dividing by 1,000. For example, 80 µm = 0.08 mm.

How thick is hair in nanometers?

Multiply micrometers by 1,000. For example, 80 µm = 80,000 nm.