The best estimate of scientists trying to quantify the size of the universe place estimates on the observable portion at 46 billion light years from earth to the observable edge, or approximately 91 billion light years in diameter. However, there are some fundamental flaws with this approach.
The portion of the universe that is observable depends on the position of the observer. This model assumes that the Earth is at the center of the universe, which may be true from an observation perspective but is highly unlikely in reality. Also, under the theory of relativity, the fixed speed of light and the continuous expansion of the universe at various speeds makes accurately determining the size impossible, since scientists have no idea what is beyond the observable portion of space. Additionally, information from the Hubble telescope indicates that the rate at which the universe is expanding is accelerating, and it is likely to do so forever.