If you want to make a rectangle a certain size in Illustrator, follow these simple steps:

  1. Open the Illustrator file you want to resize.
  2. Select the Rectangle tool (M).
  3. In the Options bar, set the Width and Height fields to the desired dimensions. (You can also enter values in pixels if you prefer.)
  4. Click and drag to draw your rectangle. (If it’s not resizing as you expect, try clicking and dragging inside the bounds of the rectangle first.) ..