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Telescope Magnification Calculator
Verified formula Updated Jun 2026 Private — runs on your device
Verified formula
Private
Magnification
48.0
For general information only — not financial, tax, legal or medical advice. Verify before you rely on it.
How to use the Telescope Magnification Calculator
The Telescope Magnification Calculator works out your magnification in an instant. Enter telescope focal length and eyepiece focal length and the result updates as you type — it is free, needs no sign-up, and runs entirely in your browser so your figures stay private.
- Enter the telescope focal length.
- Enter the eyepiece focal length.
- Read off your magnification — the calculator updates automatically, with no button to press.
Formula
The Telescope Magnification Calculator uses the formula:
Magnification = Telescope focal length ÷ Eyepiece focal length
Worked example
For example, with telescope focal length of 1,200 mm and eyepiece focal length of 25 mm, the magnification is 48.0.
| Telescope focal length | 1,200 mm |
|---|---|
| Eyepiece focal length | 25 mm |
| Magnification | 48.0 |
|---|
Results are estimates for educational use, not professional advice.
Frequently asked questions
Divide the telescope's focal length by the eyepiece's focal length. A 1200 mm scope with a 25 mm eyepiece gives 48× magnification.
No. Too much magnification dims and blurs the image. Useful magnification is limited by aperture and sky conditions.
A common guide is about 2× the aperture in millimetres, beyond which the image quality drops sharply.
Swap eyepieces. A shorter focal-length eyepiece gives higher magnification; a longer one gives a wider, lower-power view.
Enter the telescope focal length. Enter the eyepiece focal length. Read off your magnification — the calculator updates automatically, with no button to press.
Related guides
Telescope Magnification Table: Magnification by Telescope focal length
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How to Calculate Telescope Magnification: Formula, Steps & Examples
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Escape Velocity Table: Escape velocity by Mass of the body
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