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How Big is a ... ?

The head of a pin is about 2mm in diameter. Use this animation to compare the relative sizes of cells and organisms sitting on a pinhead. Nearly invisible without magnification, dust mites dwarf pollen grains and human cells. In turn, bacteria and viruses are even smaller.

To view this animation on Apple or Android phones and tablets, get Puffin Browser.

Download this animation and its matching PowerPoint® ($).



How to use:

  • Use the left and right arrows to change magnification.
  • Click on the magnifications (1, 10, 100...) for a "Power of Ten" zoom.
  • Choose an individual cell or organism (right) to bring it into view.
  • Use the scale to measure individual cells.

1 millimeter = 0.001 meter
1 micron = 0.000001 meter
1 nanometer = 0.000000001 meter


The Cast of Characters


Dust Mite

These specks at the limit of human vision may become noticeable when they move. Commonly found in rugs and mattresses, dust mites feed on flakes of skin shed by humans and pets. Dust mite feces can cause a skin rash, and other allergic and asthmatic reactions. Read more about dust mites here.

Ragweed Pollen

This pollen is produced by a weed that blooms in late summer through early fall. It is a common cause of seasonal allergic reactions.



This comprises three different white blood cells important in the immune system, -- T-cell, B-cell, and NK (natural killer). The cytotoxic T-cell can fight infections and tumor cells and working together, T-cells in conjunction with B-cells are responsible for the production of antibodies.


Red Blood Cell

Iron-rich hemoglobin gives these cells their red color and is responsible for the red cell's primary function, absorbing oxygen in the lungs and releasing that oxygen throughout the body.


Baker's Yeast

This single-celled fungus (Saccharomyces cerevisiae) is the leavening agent used in making bread through the conversion of sugar into into CO2 and ethanol. It is the CO2 which is responsible for bread's airy texture. Related to baker's yeast is brewer's yeast, a different strain of the same organism which produces larger proportion of ethanol, hence its use in making beer.


E. coli

Most of the cells in the human body are actually bacteria, not human. The majority of those bacteria reside in the intestine. One of them is the Gram-negative rod Escherichia coli (E. coli). Although most E. coli are harmless, some strains can be pathogenic. And it is those pathogenic strains that most often make the news. See E. coli growing in culture and killed by penicillin.



These bacteria are Gram-positive cocci commonly found on the skin and in the nose. As is the case with E. coli, most Staphylococcus strains are harmless, and it is the pathogenic strains such as Methicillin-resistant Staphylococcus aureus (MRSA) that get the headlines.

Ebola virus (genus Ebolavirus)

This viral pathogen causes a devastating hemorhagic fever with a high death rate. Transmission is through contact with bodily fluids of an infected individual. Currently (October 2014), the vast majority of cases are limited to countries in western Africa.


Rhinovirus, a species within the genus Enterovirus, is responsible for most common colds. It is among the smallest viruses.



Some Keywords:

metric system, micron, angstrom, virus, bacteria, nanotechnology


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