Sketchbooks come in landscape and portrait orientation. You will sometimes see references to “A” sizes which are international sizes (I indicate next which A sizes are close). Common US sizes are 4”x6” (A6), 5”x 8 1/2” (A5), and 8 1/2”x11” (A4). Of course, there are many varieties beyond these.
I am a photographer, sketcher, and watercolor painter. I offer training on learning how to use your camera more efficiently as well as on sketching and watercolor painting. In addition, I sell originals and prints of my watercolor paintings.