Converting Eyeglass prescription to Contact lenses prescription?

I'm just wondering how does it work? Is it possible to convert eyeglasses prescription to contact lenses prescription without going to the optometrist? I want to order some colored contacts online with prescription. My eyeglasses prescription is 250, but i just wanna know what my contact lens prescription will be. Is it -2.5?

Theres no mathmatical way to convert your glasses prescription to a contact lens prescription but the actual powers are usually fairly similar. The main obstacle is that the optometrist measures the shape of the cornea as a contact lens prescription is made of power and diametre needed for a particular type of lens depending on its compostion.
In short your cl prescription probably will be around a -2.50 but the fit will be a shot in the dark!

She's right. The doctor tells you what your prescription is.

Most times the eyeglass prescription has to be modified for contacts, but you have one that doesn't. Your contact prescription is also -2.50

Forget it. Its not legal to dispense contact lenses without a prescription.

So many factors go into determining an RX that it really is impossible to determine without a thorough eye exam. Sorry.

Your contact lens prescription isn't -2.50 - the power of your lens will probably be -2.50 but that's not the whole story.

More important is that the lens fits properly so it doesn't damage your eye.

That's why you need a professional to fit them properly.

Since your prescription is very minor, your contact and glasses prescription will be the same.