Microscope Magnification Calculator
Work out total microscope magnification from the objective and eyepiece, plus the field of view diameter.
Total magnification is simply the objective lens power times the eyepiece power. A 40× objective with a 10× eyepiece gives 400×. If you also know the eyepiece's field number, it works out the field of view — the diameter of the circle you actually see, in millimeters.
Total magnification
400×
Field of view diameter
0.5mm
How it works
A compound microscope magnifies twice: once at the objective lens near the specimen and again at the eyepiece you look through. Total magnification is just those two powers multiplied together.
So a 40× objective paired with a 10× eyepiece gives 400×. Swap in a different objective or eyepiece and the total scales straight from the two numbers you enter.
If you also know the eyepiece's field number — the diameter of the view it shows, in millimeters — the tool divides it by the objective power to give the real field of view: how wide a patch of the slide you're actually seeing.
Frequently asked questions
Why divide by only the objective for field of view?
The field number describes what the eyepiece reveals, and the objective is what shrinks that view down onto the specimen. Dividing the field number by the objective power gives the actual diameter on the slide.
Where do I find the field number?
It's usually printed on the eyepiece, right after the magnification — something like 10×/20 means a 10× eyepiece with a field number of 20. If you can't find it, leave that box blank and you'll still get total magnification.
Does higher magnification always mean a better view?
Not on its own. As magnification climbs, the field of view shrinks and the image dims, so you see less at once. The best power depends on what you're trying to see, not just the biggest number.