How to size a microwave
Measure the cutout, not the existing unit
Over-the-range microwaves require a 30″-wide cabinet above the cooktop with 16″ minimum clearance from the stovetop. Built-in trim kits add 1–2″ to the unit's width and 1–2″ to its height — the cabinet opening must match the trim kit, not the microwave alone. Countertop microwaves only need their footprint plus 3″ clearance on the back and sides for ventilation.
Plumbing and electrical reduce usable depth
Supply lines, drains, vent ducts, and electrical run in the back 3–4″ of most cabinets. The catalog dimension assumes those connections sit flush against the back wall. If a previous installation routed lines along the side, the new unit may not fit even though the cutout looks correct. Pull the existing unit before ordering to confirm.
Standard vs. compact sizing
Compact countertop: 0.7–1.0 cu ft, 18″×12″×11″. Mid-size: 1.1–1.6 cu ft, 21″×12″×12″. Full-size: 1.7–2.2 cu ft, 24″×17″×14″. Wattage scales roughly with capacity (700W small, 1000W mid, 1200W+ full).
Common mistakes
- Assuming all "standard" units in the same category are interchangeable. Cabinet height varies by 1–2″ between brands.
- Adding new flooring under the existing unit; the new layer traps the unit under the counter.
- Ignoring door swing or pull-out clearance in front of the unit.
- Mixing US and EU standards. EU appliances are sized in centimetres (60 cm ≈ 23.6″), not 24″.