How to Determine Magnification
To determine the magnification of a telescope, divide the telescope focal length by the eyepiece focal length. It is the formula:
Magnification = Telescope FL / Eyepiece FL
If you already know the magnification capabilities of your telescope, the ability to know what magnification you'll be working with using a given eyepiece is useful information.
The maximum magnification is the highest effective magnification a telescope can provide before it no longer provides any further detail. To calculate this, multiply the telescope aperture by 2.
Max Magnification = Telescope Aperture * 2