The Size of SARS-CoV-2 and its Implications

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The size of any viral or bacterial particle can provide a useful insight into how these infecting species can wreak havoc on host cells.

SARS-CoV-2 Virus

Image Credit: Kateryna Kon/

Size of SARS-CoV-2

Since the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was first identified in December of 2019, many infectious disease specialists, as well as researchers for almost every avenue of medicine, have been investigating how this virus spreads to and infects human beings, the wide range of severe health effects it can cause and ultimately what drugs will be able to effectively kill this virus safely.

In addition to mechanistic information, researchers have also evaluated the size and content characteristics of the SARS-CoV-2 particles. Upon analysis of negative-stained SARS-CoV-2 articles by electron microscopy, different researchers have had varying results, but the diameter of the virus has been found to range between 50 nm to 140 nm.

In addition to measuring the spherical size of the virus particle, it has also been confirmed that the length of the size tumors surrounding the outermost surface of SARS-CoV-2 can vary in length from 9 to 12 nm.

Why does size matter?

Around the world, health officials have agreed that wearing masks can prevent the spread of the virus between individuals. While this may be true, certain masks are considered much more effective at minimizing the risk of exposure, particularly N95 masks.

Whilst N95 masks from different producers may have slightly different specifications, the protective capabilities offered by N95 masks are largely attributed to the masks’ obligation to remove at least 95% of all particles with an average diameter of 300 nm or less.

The size of a virus particle largely determines how individuals can protect themselves and those around them from acquiring SARS-CoV-2. Knowing the size of a single virus particle can also allow researchers and healthcare providers to infer the amount of virus individuals are exposed to through different routes.

For example, respiratory droplets are typically 5-10 micrometers (µm) in length; therefore, it can be inferred that an individual who ingests, inhales, or is otherwise exposed to SARS-CoV-2 positive respiratory droplets can be exposed to hundreds or thousands of virus particles which increases the probability of infection.

Respiratory droplets can be transmitted through coughing, sneezing, contact with contaminated surfaces, or even through inhaled aerosols; therefore, each individual must take adequate steps to reduce their exposure to these particles by wearing masks and practicing safe social distance measures.

How Coronaviruses Work

How does it compare to other viruses?

To date, research has shown that the viruses that have been identified and isolated can range in diameter size from 20 nm to as large as 500 nm. Aside from spherical virus particles like SARS-CoV-2, whose diameters provide information on their sizes, the length of rod- or filament-shaped viruses can measure to as long as 1,000 nm.

Viruses, particularly those that originate from animals like SARS-CoV-2, can differ greatly in their size. The smallest known animal viruses are icosahedrons, which belong to the Paroviridae and Picornaviridae families and can have a diameter ranging between 20 and 30 nm.

Comparatively, the largest and most complex virus currently known to man is the giant Mimivirus, which has a total particle diameter, of which includes the fibers that extend out from the capsid, of approximately 750 nm.  

Varying Virus Sizes

Image Credit: Meletios Verras/

Comparing bacteria and SARS-CoV-2 sizes

The SARS-CoV-2 virus is a much smaller particle compared to the primary models for bacterial cell biology, including Bacillus subtitles, Staphylococcus aureus, and Escherichia Coli and Caulobacter crescentus, all of which have a cell volume that ranges from 400 nm to as large as 3 µm (3000 nm).

The large size of such bacterial species often contribute to their diverse reproductive strategies and ultimately maximize their ability to produce and release large offspring.

Whilst size comparisons between viruses and bacteria can be useful to researchers, it is also useful to compare the size of SARS-CoV-2 to other things that are encountered daily. For example, a dust mite is typically 200 µm in size. If we take a 100 nm SARS-CoV-2 particle, this makes the dust mite 2000 times larger.



Further Reading

Last Updated: Feb 15, 2021

Benedette Cuffari

Written by

Benedette Cuffari

After completing her Bachelor of Science in Toxicology with two minors in Spanish and Chemistry in 2016, Benedette continued her studies to complete her Master of Science in Toxicology in May of 2018. During graduate school, Benedette investigated the dermatotoxicity of mechlorethamine and bendamustine; two nitrogen mustard alkylating agents that are used in anticancer therapy.


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  1. Ed Hodgkins Ed Hodgkins United States says:

    Smaller particles are affected more so by Brownian motion and are more apt to be captured by nearby thread.  It is therefore logical that the mask would capture smaller objects more efficiently.  None of these things measuring as small as nanometers travel in a directly line.  There are a lot of forces at work.

    • Ken Largent Ken Largent United States says:

      So what I hear from you is that small round pegs are blocked by big square holes better because small round pegs don't travel in straight lines.

      What I gather from the article is that filter material intended to block "most" particles of a certain size are assumed to be effective against particles that are 2,000 times smaller.  Under his flawed logic, the material we use to keep flies out of our houses would also make great insulation material against the cold.

      Here is reality:  a filter material that is effective against particles of a certain size cannot be as effective against particles 2,000 time smaller.

      Even though there are masks capable of filtering out smoke particles, firefighters still use an oxygen source instead of masks because masks do not create oxygen in an oxygen depleted atmosphere AND there are other toxins besides smoke in a typical fire that a mask cannot filter out.

      The math says that particles that are 2,000 times smaller than the targeted substance are 200 times MORE likely to pass through the filter material than the "acceptable" 5 percent.

      • Greg Phillips Greg Phillips Canada says:

        The theory refers to particles that are 1/10th of a micron. Material used to keep flies out of our houses is about 20,000 times larger.

      • Greg Phillips Greg Phillips Canada says:

        Google it. Robert Brown. Brownian Theory of Motion. Larger particles have the mass to follow an airstream and flow in straight lines. Smaller particles don't have the mass and therefore they zig-zag around instead of following the airstream, and don't move in straight lines. They get bounced around and that is why they are easier to capture than larger particles that move in straight lines.

        • Carlo Wood Carlo Wood Netherlands says:

          They bounce against air molecules, causing them to have an effective diameter larger than their real diameter. However, the effective diameter is at all times LESS than that of a particle with a (slightly) larger diameter. The net result is that smaller particles get captured LESS often. The Brownian motion might cause them to be captured  more often than what would be the case in a vacuum, it is still much much less than 95%. Lets say their effective diameter becomes 10x larger (which I doubt) then the holes are still 200 times larger and they'll fly through with the air unimpeded.

        • Allen Hall Allen Hall United States says:

          The virus when constrain in saliva, TRAVELS WITH the saliva - which wicks thru the mask.

          N95 masks do not stop Virus sized particles period- Yes they do stop saliva droplets.
          BUT WHAT HAPPENS TO THE SALIVA that's trapped in the mask. It wicks thru the paper, carrying the virus with  it until it reaches the surface of the mask. There the saliva EVAPORATES and releases ALL the virus that would have otherwise been constrained by the saliva - WHICH would have fallen immediately to the ground within a few minutes. INSTEAD every time you exhale you now produce a Giant cloud of AIRBORNE virus which stays in the air for HOURS!  Don't believe it?? Then get a cigarette Take a big puff and exhale thru that stupid paper mask.. Can you still smell the smoke in the air?? You bet ya can, and smoke particles are 20 TIMES LARGER than virus !! You people gotta smarten up.. This has never been about keeping people safer - It actually SPREADS THE VIRUS FASTER

  2. Wickrama Donald Wickrama Donald Sri Lanka says:

    how do you measure the size of covid virus,it is electron microscope?

  3. Robert Larson Robert Larson United States says:

    N-95 masks are intended to protect from virus sized particles. Other masks are thought to provide protection from aerosolized droplets containing thousands of virus particles. These masks are overwhelming the type of masks being worn by the public and being potentially mandated going forward. However the non-N-95 masks do not provide protection from virus sized particles based on the observations in the article.

    If a non-N-95 mask wearer is "sprayed" by aerosolized droplets from an Covid infected person and these droplets do indeed contain significant amounts the virus, does not the mask itself then hold the droplets in place, providing an actual source for infection for as long as the Covid virus survives on the surface of the mask, while not providing protection from those virus particles? Non-science analogy - putting up a chain link fence around your yard, to protect you from mosquitos? Non-scientist just asking...

  4. C Wood C Wood United States says:

    You guys are missing the key point about N95-the non woven electret layer.  Particles smaller than 30 microns are strongly attracted by vanderwahls forces to the charged fibers and are very effectively filtered.  Well explained by MinutePhysics on YoutTube:

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News Medical.
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