You are standing in the garage with a spare refrigerator, or a catalog open to a chest freezer, and the question is whether it fits your house. The answer depends less on the box than on how your household actually eats and where the unit will sit.
Start with the load you really carry
Walk the kitchen and count what goes into the fridge in an ordinary week. Note the bulk items: the cases of drinks, the batch cooking, the holiday roast that waits in the freezer between seasons. A spare unit is for overflow and bulk storage. If the main refrigerator is already full most days, a spare answers a real need. If it sits mostly empty, a spare just adds cold air to a room nobody opens.
Measure the space, then the clearance
Measure height, width, and depth at the exact spot you have in mind. Add the clearance the manufacturer's installation guide asks for at the back and sides, because the unit releases heat and needs air to do it. Check the door swing too. Open the door fully in your head, then with the cardboard shape of the box, and confirm it does not hit a wall, a shelf, or the car.
Check the floor and the route
A garage floor is often sloped toward the door. A unit that is not level will not seal well and can strain its own door. Put a level on the top surface before you commit. Then trace the delivery path: doorways, turns, steps, and the width of the hallway between the garage and the unit's final place. Many arrivals fail at the second doorway, not the first.
Check the outlet and the circuit
Look at what else shares the outlet's circuit. A refrigerator on a crowded circuit with a freezer, a heater, or a power tool can trip at the wrong moment. Ask a licensed electrician to confirm the outlet and circuit are suitable before you plug in. Do not run the unit on an extension cord or a power strip.
Check the room's temperature range
Garages get hot in summer and cold in winter. Many standard refrigerators are built for a narrower indoor range. Look in the owner's manual for the stated ambient temperature range before you place a unit in an unheated or uncooled space. Chest freezers and refrigerators can differ on this point, so read the page for the exact model.
Compare the age before you accept a used unit
If the spare is used, ask how old it is and how it has been stored. Then compare that age against the typical service life on the appliances ranked by typical service life page. Age is a planning input. It tells you how soon to think about a replacement, not whether the unit is good today.
Before it comes home, confirm these
Measure the spot with clearance. Confirm the door swing. Level the floor. Trace the delivery route. Check the outlet and circuit with an electrician. Read the room temperature range in the manual. Note the age of any used unit. If each of those answers is clear, the spare fits your household, not just your wall.