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Biology Tools · Updated October 21, 2026 · Reviewed by FormatFlow Editorial

Microscope Magnification Calculator

You can work out the total magnification of a microscope from the objective and eyepiece powers, and convert a measured field of view to another magnification with the steps shown.

Runs in your browserFree · No sign-up · No watermark
OBJECTIVE × EYEPIECE → TOTALRuns in your browser
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Everything runs locally in this tab. No file is uploaded while the tool loads.

This tool runs in your tab. Nothing is uploaded and no copy is stored.

How files are handled

At a glance

Works with
OBJECTIVE × EYEPIECE → TOTAL
Processing
In your browser
Price
Free, no account
Updated
October 21, 2026
All Biology Tools

About Microscope Magnification Calculator

Total magnification is one of the first calculations in a microscopy practical: multiply the objective power by the eyepiece power. A 40× objective with a 10× eyepiece gives 400×, and the same arithmetic applies to any combination of lenses in the optical path.

Field of view is the other half of the problem. If you know the diameter a field of view covers at one magnification, it shrinks in inverse proportion at a higher one, which is what allows a measured distance to be converted between magnifications. This calculator does both and shows the substitution at every step.

What this tool does

The details that matter when you use Microscope Magnification Calculator for real work.

  • Total magnification

    Objective × eyepiece in one step, from 4× and 10× low-power views up to 100× oil objectives.

  • Field-of-view conversion

    FOV₂ = FOV₁ × M₁ / M₂ converts a measured field diameter from one magnification to another.

  • Millimeters and micrometers

    Enter the field of view in mm or µm and see the converted value in the unit you chose plus the other unit.

  • Step-by-step working

    The formula is shown with the numbers substituted, so the result can be copied into a lab report.

  • Clear input validation

    Empty, zero and negative values get an inline message instead of a wrong answer.

  • Assumptions stated

    The result lists the conditions: same eyepiece and optical path, no extra lenses and a linear field diameter.

How to use Microscope Magnification Calculator

No account, no installation — the whole job happens in this browser tab.
  1. 01

    Enter the objective magnification

    Read the number printed on the objective lens and type it in, for example 40 for a 40× lens.

  2. 02

    Enter the eyepiece magnification

    Use the eyepiece power, usually 10× or 15×.

  3. 03

    Read the total magnification

    The result shows objective × eyepiece = total, with the substitution worked through.

  4. 04

    Add a field-of-view measurement

    Optionally enter a measured field diameter, the magnification it was measured at, and the target magnification; leave the target blank to use the calculated total.

  5. 05

    Check the assumptions

    Confirm that the same eyepiece and optical path were used, then copy the working into your notes.

How this tool works

Works with
OBJECTIVE × EYEPIECE → TOTAL
Processing
Client-side, in your browser. Nothing is uploaded.
Requirements
Chrome, Edge, Firefox or Safari · JavaScript enabled

Limitations worth knowing

  • The field-of-view conversion assumes the same eyepiece and optical path at both magnifications; extra lenses, camera adapters or a different eyepiece invalidate the simple ratio.
  • Real field diameters can differ from the calculation because of the objective's field number, tube lens and measurement method, so treat the converted value as an estimate.
  • It calculates optical magnification only and does not account for empty magnification, diffraction limits or digital zoom in a camera image.

Privacy and file handling

The objective, eyepiece and field-of-view values are used only in this browser tab. All calculations run with JavaScript on your device, so nothing is uploaded, stored or logged, and the page keeps working offline.

Read the full privacy policy

Microscope Magnification Calculator FAQ

Short, direct answers to the questions people ask before using this tool.
How do I calculate total microscope magnification?
Multiply the objective magnification by the eyepiece magnification. A 40× objective with a 10× eyepiece gives 400× total, and a 100× oil objective with the same eyepiece gives 1000×. The calculator also shows the multiplication with the numbers filled in.
What is the field-of-view conversion formula?
FOV₂ = FOV₁ × M₁ / M₂, where FOV₁ is the diameter measured at magnification M₁ and FOV₂ is the diameter at magnification M₂. For example, 4.5 mm at 100× becomes 4.5 × 100 / 400 = 1.125 mm at 400×.
Why does the field of view get smaller at higher magnification?
Higher magnification spreads the same sample over a larger image, so the area visible at once shrinks. For a fixed optical path the field diameter is inversely proportional to magnification, which is why doubling the power halves the visible diameter.
Which magnification values should I use for M₁ and M₂?
Use the total magnification at each setting, meaning objective × eyepiece. If the eyepiece and the rest of the optical path stay the same, using just the objective powers gives the same ratio because the eyepiece factor cancels out.
Why does my measured field of view differ from the formula?
The simple ratio assumes identical optics apart from magnification. Eyepiece field numbers, tube lenses, camera adapters, parfocality and measurement error can all shift the real value, so treat the converted diameter as a good estimate and confirm with a stage micrometer when precision matters.
Can I use this for camera adapters or stereo microscopes?
Only when the same optical path is used for both magnifications. A camera adapter adds its own magnification factor, and stereo microscopes often change the optical path as the zoom ring moves, so the inverse ratio may not hold; check the manual or calibrate with a ruler.
What units does the calculator use?
Field of view can be entered in millimetres or micrometres. One millimetre is 1000 micrometres, and every result shows the converted diameter in the unit you chose plus the other unit, so no manual conversion is needed.
Are the values I type uploaded anywhere?
No. The objective, eyepiece and field-of-view numbers are used only in this browser tab. All calculations run with JavaScript on your device, so nothing is uploaded, stored or logged.

Background reading

Format guides that explain the trade-offs behind Microscope Magnification Calculator.