Built-In Microwave Cutout Sizes
Built-in microwaves install into a cabinet opening — the cutout — using a trim kit. The single most important rule: the cutout is bigger than the microwave, and its size is set by the trim kit, not the microwave body. Here are the standard 24, 27, and 30-inch openings, plus how to measure yours.
| Nominal size | Opening width | Opening height | Depth |
|---|---|---|---|
| 24" Compact built-ins; common in apartments and tighter cabinetry. | 22½–23" | 17–17½" | 22–24" |
| 27" Mid-size openings; pairs with 27" wall-oven cabinetry. | 25–25½" | 17–17½" | 22–24" |
| 30" The most common full-size built-in opening. | 28½–29" | 17–18" | 23–24" |
Approximate rough-opening figures for planning. The exact cutout is specified by your model's trim kit installation sheet — always cut to that, not to this table.
Across 696 current models, 75 are dedicated built-in units and 87 are trim-kit compatible. Most built-in bodies are nominal 24-inch (39 models) or 30-inch (22 models).
Cutout size vs. microwave size
This trips up most first-time installers. A 30-inch built-in microwave does not need a 30-inch hole — it needs the opening its trim kit calls for, which is a bit under 30 inches wide and about 17–18 inches tall. The trim kit frames the gap between the microwave and the cabinet and provides the ventilation path. Build the opening to the trim kit, drop in the microwave, attach the frame.
How to plan a built-in cutout
- Pick the microwave first, then buy its matching trim kit — kits are model-specific, not universal.
- Cut to the trim kit's spec from its installation manual, never to the microwave's body dimensions.
- Check depth and the outlet. The cabinet must be deep enough for the body plus the cord, and an outlet must sit where the manual shows it.
- Keep vents clear. The kit supplies the air gap; don't block the louvers or recess the unit past the spec.
The trim-kit-compatible alternative
If you want the built-in look without a dedicated built-in unit, many countertop models are trim-kit compatible — the manufacturer offers a matching kit to recess them flush. It's often cheaper and gives you more model choice than the dedicated built-in range.
Don't forget the clearances
Even with a trim kit, the manufacturer specifies minimum clearances for safe ventilation. MicrowaveFit lists each model's required clearances and can check them against your space — useful before you commit to cutting cabinetry. See how fit scoring works.
Frequently asked questions
What is the standard cutout size for a built-in microwave?
Built-in microwaves use nominal 24, 27, or 30-inch trim kits. The actual rough opening is slightly smaller than the nominal size — roughly 22½–23 inches for a 24-inch kit, 25–25½ inches for a 27-inch kit, and 28½–29 inches for a 30-inch kit, by about 17–18 inches tall. Always confirm against the exact trim kit's installation sheet.
Is the cutout the same size as the microwave?
No. The cutout (the cabinet opening) is larger than the microwave body so the trim kit can frame it and air can circulate. Order the trim kit matched to your microwave model, then cut the opening to the trim kit's spec — not to the microwave's dimensions.
Do I need a trim kit for a built-in microwave?
Yes for a flush, finished look. Many countertop microwaves are "trim-kit compatible," meaning the manufacturer sells a matching kit that lets you recess them into cabinetry. A purpose-built built-in model still needs its matching trim kit for the cutout to look right and vent correctly.
How much ventilation clearance does a built-in microwave need?
The trim kit provides the required air gap, but you must still build the opening to the manufacturer's spec and keep vents unobstructed. Never seal a microwave into a tight box without the specified clearances — it can overheat.