What is magnification?

Magnification is the ratio of the size of the image produced by an optical instrument to the actual size of the object. A magnification of 10x means the image appears ten times larger than the object.

How is telescope magnification calculated?

Telescope magnification equals the objective (main mirror or lens) focal length divided by the eyepiece focal length. For example, a 1000 mm objective with a 10 mm eyepiece gives 100x magnification.

How is compound microscope magnification calculated?

Total microscope magnification is the objective lens magnification multiplied by the eyepiece magnification. A 40x objective with a 10x eyepiece gives 400x total magnification.

What does a magnification less than 1 mean?

A magnification less than 1 (e.g. 0.5x) means the image is smaller than the object — the object has been reduced. This occurs with wide-angle optics or when the image distance is shorter than the object distance.

Do I need to use the same units for image and object size?

Yes. Both the image size and object size must be in the same unit (mm, cm, inches, etc.) for the ratio to be correct. The magnification result is dimensionless.

What is the difference between angular and linear magnification?

Linear magnification compares physical sizes (image size / object size). Angular magnification compares the angle subtended by the image to that subtended by the object. This calculator uses linear magnification, which is the most common form used in microscopy and photography.

Magnification Calculator

Name: Magnification Calculator
Availability: InStock
Author: Nham Vu

Calculate magnification from image and object sizes, or from objective and eyepiece focal lengths.

Magnification Method

Image Size

Size of the image as seen or measured

Object Size

Actual physical size of the object (same unit)

Formulas

M = image size / object size Size ratio method
M = f_obj / f_eye Telescope (focal lengths)
M = M_obj × M_eye Compound microscope

Enter values and click Calculate to find the magnification.

Summary

Calculate magnification from image and object sizes, or from objective and eyepiece focal lengths.

How it works

Choose a calculation method: Size Ratio or Lens Focal Lengths.
For Size Ratio: enter the image size and the actual object size in the same units.
For Lens method: select Telescope or Microscope, then enter the relevant focal lengths or magnifications.
Click Calculate to see the magnification factor instantly.
A magnification greater than 1 means the image is larger than the object; less than 1 means smaller.
Clear the inputs and switch methods to explore different optical setups.

Use cases

Biology students calculating microscope magnification for lab reports.
Astronomers comparing eyepiece and objective focal lengths for telescope setups.
Photographers determining macro lens magnification from subject and image size.
Teachers demonstrating how magnification changes with different lenses.
Jewelers checking loupe magnification against measured image size.
Engineers verifying optical system specifications.
Science fair participants documenting experimental magnification.
Hobbyists selecting the right eyepiece for a target magnification.

Frequently Asked Questions

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Last updated: 2026-05-23 · Reviewed by Nham Vu