And that would be radius of the universe, not the full diameter. It would 13.7 * 2, or 27.4 billion light years. But really, those are all theoretical models - some scientists would say it is a perfect sphere, some would say it is relatively flat, some would say it is hyperbolic. Some would say the matter expanded in just 1 direction, not in every direction. You can't say that it is larger than the speed of light allows it to be, though.
27.4 billion light years? Ok, but the size of the
observable universe is a sphere with a radius of about 46 billion light years and growing by the second ^^