🔭 Telescope Magnification Calculator
Find how much a telescope magnifies the view based on its focal length and the eyepiece you’re using.
What telescope magnification means
A telescope’s magnification is the ratio of its focal length to the focal length of the eyepiece being used: Magnification = Telescope Focal Length ÷ Eyepiece Focal Length. Swapping in a shorter eyepiece increases magnification.
How this calculator works
Enter the telescope’s focal length, the eyepiece’s focal length, and the telescope’s aperture (objective lens or mirror diameter). The calculator computes magnification, the exit pupil (aperture ÷ magnification, which affects how bright the image looks), and the focal ratio (focal length ÷ aperture, often written as f/ #).
Very high magnification numbers on paper aren’t always usable in practice — atmospheric conditions and the telescope’s aperture limit how much detail is actually visible. This calculator is for general planning and educational purposes.