A dryer is a fixed installation as much as an appliance. Before you choose a size or a model, measure the closet, the vent path, and the way your household uses the machine. The fit decides whether the machine runs the way it was designed to.
Measure the space
Take the width, depth, and height of the closet or nook with the door open. Note where the power supply and any gas line enter the space and how close they sit to the back wall. Leave room for the cord or hose and for you to reach the back panel. Measure the door opening too, because a tight entry path makes a large drum hard to bring in.
Trace the vent run
The exhaust path is the part most often overlooked. Follow the duct from the back of the dryer to the outside termination. Count the bends, because each bend adds resistance to airflow. Note the duct material and whether it is rigid or flexible. A shorter, straighter run with fewer turns is easier on the machine and easier to keep clear of lint. If the path is long or crooked, check the dryer manual for the allowed run before you choose a model. The clothes dryer page on this site gives the general service life picture and what to plan for.
Describe the household load
Describe how you use the machine in plain terms. Who does the laundry, how often, and whether bulky items such as comforters or towels go through the same cycle. A household that dries heavy loads every day will feel a difference in drum size and drying time that a single person doing light loads will not. Write this down before you shop so you can compare models against your own use, not against the showroom display.
Check the utility connections
Confirm the power type the machine needs and whether the outlet is already in place. For gas models, confirm the supply is already at the spot. If the current setup needs work to meet the manufacturer's requirements, that work belongs in the plan before the machine arrives. Have a licensed trade make any changes to supply lines.
Put the fit on one page
Record the closet dimensions, the door width, the vent run length and bends, the outlet type, and the household load in one place. Compare each candidate against that page. A dryer that fits the closet but not the vent path is the wrong purchase, however good the drum looks.