It can be risky to choose non prescription eyeglasses, and in particular prescription glasses online, even if you know the magnification power, for example +3.00. You can get away with it, and you can wear them. But we recommend sticking to your prescription glasses. Don't experiment with your eyes.
If you're seeking a backup pair of glasses, don't skimp on the cost of prescription reading glasses. Purchase your prescription eye glasses from your eye doctor or, if possible, by those prescription glasses online.