Start with the people. Count who does laundry in the house and how often. A household with a single adult who washes small weekly loads has different needs from a family that runs the machine every day. Write down the typical week before you look at any machine.
Next, list the bulky items. Comforters, work uniforms, dog beds, and large towels take up more drum than their weight suggests. If the house has any of these on a regular basis, the machine has to be sized for them, not only for ordinary clothes.
Then measure the space. Take the width, depth, and height of the alcove or closet, and note the door swing if the laundry sits in a small room. Add room for the hoses, the drain standpipe, and the water shutoffs. Leave clearance for the lid or door to open fully. A washer that fits the box but cannot be serviced from behind is a poor fit.
Check the floor. A full load of wet laundry is heavy. Find out whether the floor is slab or framed, and whether the laundry sits above living space. If it does, the load path matters more than the machine itself. Ask a builder or a licensed contractor before you commit to a larger unit.
Look at the drain and the water supply. Confirm the drain height and the hot and cold supply lines. Older houses sometimes have a standpipe that is set too low or too far from the machine. These details decide whether a larger machine is practical in your house.
Pair the washer with the dryer. If you already have a clothes dryer, check that its capacity suits the washer's output. A heavy load spun out and moved into a small dryer will keep the dryer running longer. Plan the pair together.
Use age as a planning input. Note the install year of the current washer and compare it with the typical service life on the clothes washer page. A machine nearing the end of its typical life is a good moment to size the replacement, because you are already measuring the space. The ranked list of major appliances shows where washers sit beside the others, and the published figures there are the ones to use for planning.
When you have the numbers, write them on a single page: household size, weekly loads, bulky items, the space's width, depth, and height, the drain height, the supply location, and the dryer pairing. Bring that page to the store or the installer. A seller who works from it is working from your house, not from the showroom floor.