Which exoplanet is closest to Earth in size?

A transiting planet's size is measured rather than inferred: it blocks a fixed fraction of its star's light on every crossing, and that fraction is a direct ratio of the two sizes. The number still carries an uncertainty of a few percent, most of it inherited from the size of the star, so every world within about 1% of Earth's radius is Earth's size as far as anyone can tell. This table lists those first, nearest to us first, since the nearest one is the one astronomers can study best, and then everything else by how close its radius comes.

Size is only one half of being Earth-like. A world the size of Earth can orbit close enough to its star to melt or far enough out to freeze, and a radius says nothing about air or water; the Earth Similarity Index, which weighs temperature alongside size, is the better single measure of that. Only planets found by the transit method are ranked, because theirs are the sizes measured geometrically, and disputed detections are left out.