This teacher resource is a collection of length measurements found within the Science Learning Hub. Lengths range from the very small to the very big.

Student activities can be developed from some of the ideas presented, and by the end of such activities, students should be able to:

  • appreciate the huge range of length measurements in use
  • use length measurement units appropriately
  • develop their understanding of the decimal system as applied to length measurement.

Planck length

1.6 x 10-35 m. Anything shorter than this makes no physical sense. It is the ‘quantum of length’ – the smallest measurement of length with any meaning.


10-18 m or 1 attometre (am). Quarks are the building blocks of protons and neutrons.
The structure of the nucleus


10-15 m or 10 femtometres (fm). The tiny, dense central part of an atom.
The structure of the nucleus

Gamma Ray

10-12 m or 1 picometre (pm). The wavelength of this highly energetic form of electromagnetic radiation.
The electromagnetic spectrum

Hydrogen atom

25 pm. The approximate diameter of a hydrogen atom.
Westpac Stadium, Wellington

Carbon nanotube

10-9 m or 1 nanometre (nm). The approximate diameter of a carbon nanotube.
Carbon nanotube​s

DNA thickness

3 nm. The distance across the ‘twisted ladder’ structure of DNA.
DNA bases


90 nm in diameter. The human immunodeficiency virus (HIV) is spherical in shape.

UVA wavelength

315–400 nm. Overexposure to ultraviolet (UV) light can damage the skin.
What is UV?

Clay particle

10-6 m or 1 micrometre (1 mm). Clay is a soft, loose, earthy material containing particles with a grain size of less than 4 micrometres (μm).
What is clay?

Fern spore

30–50 mm. Spores are produced in capsules called sporangia. These are aggregated into clusters called sori, found on the under surface of fern fronds.
What is a fern?

Naked eye limit

100 mm. The smallest structure just visible to the unaided eye is about 100 mm.

Human skin

0.5–4 x 10-3 m or 0.5–4 millimetres (mm). Depending on location, human skin varies in thickness from 0.5 mm (eyelids) to 4 mm (palms and soles of the feet).
Diagram of human skin structure


10-2 m or 1 centimetre (cm). Microwaves are used for heating food in a microwave oven or for transmitting information from one place to another.
Wavelengths of different wave types

FM radio waves (100 MHz)

Wavelength is 3 x 100 m or 3 metres (m).
Fundamentals of waves


42.2 x 103 m or 42.2 kilometres (km). The current men’s world record for the marathon is 2:03:59. Most recreational runners would take about 4 hours to complete it.
Marathon versus sprint

Earth’s diameter

~12.8 x 106 m or 12.8 megametres (Mm) or 12.8 thousand kilometres.
Earth structure

Sun’s diameter

1.4 x 109 m or 1.4 gigametres (Gm).
Distances in space

Earth to Neptune distance

4.35 x 1012 m or 4.35 terametres (Tm) or 4.35 million kilometres.
Distances in space

1 light year

9.5 x 1015 m or 9.5 petametres (Pm) or 9.5 million million kilometres. The closest star system, outside the solar system, is Alpha Centauri located about 4.37 light years away.
Distances in space

Current estimated diameter of the observable universe

~8.8 x 1026 m or 93 billion light years.


    Published 17 August 2011