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How to Calculate the Magnification of a Microscope? Formula & Cheat Sheet

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scientist using microscope

Microscopes are one of the most useful pieces of science equipment we have available today. The magnification power enables us to get a closer look at subjects we wouldn’t normally be able to see with our naked eye. 

But you might wonder, “How can I calculate the magnification of a microscope?”

That’s a good question, as it will determine how much a subject is enlarged. Grab some pen and paper, and look below to learn how to do this effortlessly!

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The Formula for Finding Microscope Magnification

To find the magnification that has affected your microscope image, you’ll need to multiply the magnification power of your eyepiece (ocular lens) by the power of your objective lens. For example, if the ocular lens shows a 10X magnification and the objective shows a 20X magnification, the total magnification will be 200X (10 x 20 = 200). 

The best way to find both of these numbers is to look at the inscriptions on the outside of each of these elements.

Parfocal Lens Microscope
Photo Credit: A-torn Jakkawanmonthon, Shutterstock

Eyepiece/Ocular Lens

The eyepiece marking may vary depending on your microscope model, but you should see a label on the ocular lens that almost always says 10X. However, some may say as low as 5X or as high as 15X. You may need a calculator if your ocular lens shows a magnification other than 10X, as it will be a challenge to calculate the results off the top of your head—unless you’re a math genius!

Objective Lens

On the objective lenses (this is the lens that is just above your sample or slide) there should also be a marking that says a magnification number, which differs on which objective lens you use. Keep in mind that there are a total of three or four objective lenses on most standard microscopes, so be sure to look at the one that is being used for viewing. 

Common numbers will be 4X, 10X, 20X, 40X, 60X, and 100X. 

There are names given for each of the objective lenses; scanning (4X), low power (10X), high power (40X), and oil immersion (100X). The oil immersion lens may not be included, as it’s found in higher-end models. It’s possible to swap objective lenses out, but you will have to find compatible options that are the same tube diameter.

close up of microscope at the laboratory
Photo Credit: Mariia Mikhailova, Shutterstock

Cheat Sheet

If you don’t want to do the math, you can probably find your total magnification by looking at our cheat sheet. This table shows the solutions to popular magnification formulas on microscopes.

  4X 10X 20X 40X 60X 100X
10X 40X 100X 200X 400X 600X 1000X
15X 60X 150X 300X 600X 900X 1500X

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What to Do If You Can’t Find the Magnifications

It’s uncommon for a microscope to exclude the magnification number on the eyepiece and objective lenses. Sometimes, wear and tear from transport can rub off the writing, especially if the eyepiece is made of low-quality materials. In this case, contact the manufacturer and let them know your microscope model number; they should be able to confirm these criteria. Still, proper storage and using safe transportation methods will be the most effective preventative measures you can perform.

Featured Image Credit: Alexander Raths, Shutterstock

About the Author Robert Sparks

Robert’s obsession with all things optical started early in life, when his optician father would bring home prototypes for Robert to play with. Nowadays, Robert is dedicated to helping others find the right optics for their needs. His hobbies include astronomy, astrophysics, and model building. Originally from Newark, NJ, he resides in Santa Fe, New Mexico, where the nighttime skies are filled with glittering stars.