General Rule of Thumb
The more powerful the lens, the smaller it will be and the closer you must hold it to the object ('working distance'). The less powerful the lens, the larger it will be and the further you can hold it from the object.
There is always a compromise between high magnification (small lens) and large lens (low magnification).
Reading Chart & Find Your Magnification
What magnification works best for me?
When looking for the right magnifier, it is important to pick which magnification level is best for you.
Below, is an example of print at each given magnified power as shown on the right hand side. Make sure to read the chart approximately 10 to 15 inches away from your eyes. The line that you can read the most with ease should be about the right magnification you will need for your magnifier.
However, keep in mind this chart is just to help, but results may not be 100% accurate and can vary.