I'm assuming you don't have a prescription for contacts and have just been winging it, which is a bad idea* because it can strain your eyes unnecessarily or even damage them. Don't risk it. See an eye doctor and get a prescription for contacts, so that when you're buying non-prescription contacts you aren't buying something that's completely wrong for your eye.
If you do already have some prescription contacts, the prescription is printed on the package and you should just be able to read it off. I'm guessing that for non-prescription lenses the sizing information they want are the BC (curvature) and DIA (diameter) numbers.
*I seriously typed "eyedea" first.
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Urania, Muse of Astronomy
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