You can figure out how many wardrobe boxes you need for a move by measuring your closet space. Most moving boxes are 24 inches wide, which means they provide 2 feet of hanging space. If your closet has a single 4-foot rod full of clothes, you would need two wardrobe boxes.
You may also need to take into account the weight of your clothes. Even the sturdiest U-Haul boxes only hold 80–100 pounds. If you have any particularly heavy clothes, you may hit the box’s weight limit before you run out of space, especially with a small or medium box.