What is the common answer to the question: How strong are your glasses?
If someone asks me, I don't know how to answer this because I'm not a native English speaker. I want to get the common answer in an English speaking country. What do the people usually say?
Though I am not an eye doctor, both my husband and I wear glasses, so I can at least explain this to you in common English.
My husband is nearsighted. This means without glasses or contacts, he cannot see things far away. If someone were to ask him the strength of his glasses (or contact lenses), he'd say a minus seven (-7). Anyone who wears glasses knows from this number that his eye sight is really bad. A minus seven means his glasses are noticeably thick.
I am not nearsighted. I am farsighted. This means I can see things at a distance just fine, but I need glasses to read. If someone were to ask how strong are my glasses, I would say they are a plus one point five (+1.5). This is not particularly strong and my vision is not particularly bad. Reading glasses for this strength can actually be bought at a drug store and do not require a prescription.
Outside of basic near- or farsightedness, the language of eyeglasses gets a little more complicated but hopefully this at least helps your basic understanding.
Essentially if someone takes your glasses, tries them on, and says," Whoa you're really blind," or,"You're eyes are really bad," that indicates that you have high strength glasses. If your sight only slightly improves when you put on glasses compared to when you don't put on glasses, then they are low strength.
Look at it as if it was a video. Low strength would be videos that are at 240p or 360p. High strength would be the 1080HD. It is kind of like that. If you can barely see without glasses and then can see everything very clear and sharp with them on, then they are high strength. If you can see pretty well, but just get a little more clarity from wearing glasses they are low strength.
If you are referring to the strength of the prescription your glasses are then you can just ask your optometrist, because that varies.