I always buy 3 1/3 yd, which is 120". So the piece is 106" x 120". Most of the 108" fabrics aren't really that wide. But then i end up with a little extra full length strips to use as borders on another quilt.
3 yards would be 3x36" = 108". And usually, rather than 1/3 yd, you have to choose 3/8 yd.