First, measure the area where you intend to place the chair, taking into account the space needed for movement around it. Keep in mind the proportions of the room and the scale of the other furniture. An oversized chair might overpower a small room, while a petite chair could look out of place in a spacious area.
When considering chair dimensions, look at the overall width, depth, and height, but don't forget about the seating area dimensions too. A chair might be wide but have a narrow seat. Similarly, the height of the seat and the backrest can significantly affect comfort, especially if you're tall or have back issues.