The soprano ukulele is the smallest size ukulele, with twelve frets and a range of twenty-two notes. It’s considered the “standard” size, measuring very closely to that of the earliest known ukes.
The concert ukulele is a little longer than the soprano and has a wider body, adding greater depth and sustain to its sound. They typically have between 15 and 20 frets, giving them a broader range of notes.
The tenor ukulele is around 6 inches or so longer than a soprano uke. Like a concert ukulele, the tenor typically has between 15 and 20 frets and has a wider body, bigger frets, fuller sound and deeper bass range.
Baritone ukuleles are large enough that they are tuned to the same notes as full sized guitars, which are (from low to high) D, G, B, and E. They have a much deeper bass range but lose some of the plinky tone associated with ukes.