Someone who needs a slight correction (or has mild astigmatism) will use reading glasses with a power of, say, 1.25, while someone who needs a strong correction (has a greater astigmatism) will need a power of up to +3. The appropriate lens power can be measured by age. Most people over the age of 40 will need reading glasses with a power of 1 or 1.25, and then they will need an additional half unit of the lens size every 10 years. However, most people who are new to reading glasses probably won’t need lenses with a high power.