Memo boards tend to come in sizes that fit neatly over a desk area. For instance, they might be around 33 inches by 27 inches. But memo boards come in a wide variety of sizes, so be sure to measure the wall space you have and shop around for the perfect size.
You can also decide if you want the memo board to be longer by orienting it horizontally or taller by orienting it vertically. If you are placing the memo board over a wide desk, it makes sense to orient it horizontally. Vertical memo boards look best on smaller walls or in more narrow spaces.
Some memo boards also come as sets, where two will have a small boxy shape and a third may be long. They fit together on the wall to give different functions, like one piece may be a chalkboard, another a corkboard and another a dry erase board. The smaller boards may be 9 inches by 9 inches, and the longer board may be around 18 inches by 7 inches. This is another good size and style to choose if you want different functions because you both hang items and write notes.