Progressive glasses,also called no-line bifocal glasses, help glasses wearers to see things clearly in different viewing distance.The proper height of this kind of lens must be a minimum of 30mm from the top edge of the lense to the bottom.
Progressive glasses allow people see clearly from far to near. So a lens of progressive glasses is usually bigger than a regualr one. The common height of progressive glasses lens must be at least 28mm. However, the height varies depending on the type and brand of the progressive glasses.
I think the size of the lenses will depend on which kind of progressive glasses you want to make. If they are just a pair of bifocal glasses, the size of the lenses will be bigger than common eyeglasses. The more focus your lenses have, the bigger the size will be. So you'd better show the opticians your prescription first and then they can choose the lenses for you.
I think the lenses of the progressive glasses can be smaller than they used to be. It is said that lens manufacturers has introduced a kind of short corridor progressive lenses with compact designs which can provide larger reading zones. This means that we can use a pair of smaller, fashionable frame to store progressive lenses too. You'd better consult an optician to know more about this. Good luck!
Take your prescription with you and see an optician in an optical shop in the nearby. He or she can tell you how big your lenses will be. Many people will suffer from blurred vision and headaches when they use progressive glasses for the first time. If you are a new beginner to wear a pair of progressive glasses, I'd like to share this information with you. It will tell you how to use a pair of progressive glasses. http://www.youtube.com/watch?v=DJkwn3lusJY Hope this helped too!