How to Measure for a Microwave Before You Buy

June 9, 2026

Tape measure showing the width and depth of a countertop microwave in a kitchen

How to Measure for a Microwave Before You Buy

Microwaves get returned more often than almost any other appliance, and it’s nearly always one of two mistakes: it didn’t physically fit the space, or it fit but a dinner plate didn’t fit inside it.

Both are avoidable in about ten minutes. What you measure depends on which kind you’re buying.

First: which type are you buying?

Type	Where it goes	The critical measurement
Countertop	On the counter or a shelf	Counter depth, plus air clearance around it
Over-the-range (OTR)	Mounted above the cooktop	30 in. from the cooktop to the microwave’s underside
Built-in / trim kit	Inside a cabinet, with a frame	The exact cabinet cutout, to the manufacturer’s spec
Microwave drawer	Under a counter or island	Cabinet width (24 or 30 in.) and drawer clearance

Measuring for a countertop microwave

The three outside dimensions

Width of the space, wall to wall or between whatever flanks it.
Depth of the counter. Standard counters are about 25 inches deep, and microwaves run 15–20 in. deep. Make sure the door can open fully without hitting anything.
Height to the underside of the upper cabinet. Most countertop microwaves are 12–14 in. tall, and you need room above.

The clearances people forget

A microwave vents heat, and it needs air. Manufacturers typically specify:

3 inches on each side
3 inches at the top
1 inch at the back

Check the specific model, but as a rule: do not box a countertop microwave tightly into a cabinet or a snug shelf. Restricted airflow makes it run hot, which shortens its life and can be a fire risk. A countertop microwave shoved into a cabinet cubby with no clearance is one of the most common installation mistakes in a kitchen.

If you want it inside cabinetry, buy a built-in model or a trim kit designed for it, which routes the airflow properly.

The measurement everyone skips: the inside

Exterior size tells you nothing about usable interior space. A compact 0.7 cu. ft. microwave has a turntable around 10 inches across, and a standard 10.5–11 inch dinner plate will not turn in it. It may not even fit flat.

So before you buy:

Measure your dinner plate. Seriously. Then check the model’s turntable diameter.
Check the interior height if you reheat casserole dishes or tall mugs.

Capacity	Turntable (approx.)	Fits
0.7 cu. ft.	~10 in.	Mugs and small bowls. A dinner plate often won’t rotate
0.9–1.2 cu. ft.	~11–12 in.	A standard dinner plate. The practical minimum
1.4–1.6 cu. ft.	~12–14 in.	Plates, casserole dishes, most containers
1.8–2.2 cu. ft.	~14–16 in.	Large platters and baking dishes

And check the wattage while you’re at it, 900–1,200W cooks properly, below 800W and everything takes noticeably longer. It’s the spec that matters most after size.

Measuring for an over-the-range microwave

An OTR has to satisfy the cabinet above, the cooktop below, and the wall behind. The numbers:

Cabinet opening: 30 inches wide. Standard, but measure at the front and back, trim can steal half an inch.
30 inches of clearance from the cooktop surface to the bottom of the microwave. This is a safety spec, not a preference.
66 inches minimum from the floor to the bottom of the microwave.
Depth: OTRs are 15–18 in. deep and will protrude past your 12-inch upper cabinets. That’s by design, it puts the fan over the front burners.
The vent path: up through the cabinet, out the back wall, or recirculating. Find this out before you buy.

The full walkthrough, including mounting and electrical: how to measure for an over-the-range microwave. And if you’re still deciding between the two types, over-the-range vs. countertop microwaves.

Measuring for a built-in or trim-kit microwave

Here, precision matters more than anywhere else, because the microwave sits inside a hole with a frame around it.

Get the manufacturer’s cutout spec sheet for the exact model, and build or verify the opening to it. Don’t measure the old microwave and assume.
The trim kit is model-specific. A trim kit for one model won’t fit another, even from the same brand.
Confirm the outlet location. It must be inside or adjacent to the cabinet, and it must not interfere with the unit sliding back.
Never install a plain countertop microwave inside a cabinet with a trim kit unless the manufacturer explicitly says that model supports it. Airflow is engineered per model.

Microwave drawers

Increasingly popular in remodels because they clear the counter and the wall, and you pull down instead of reaching up (which is genuinely better for kids and anyone shorter).

Standard cabinet widths: 24 or 30 inches.
They need a dedicated cabinet cavity and a nearby outlet.
They cost considerably more than any other type, and they’re a remodel decision, not a swap. See best cooking appliances for a kitchen remodel.

The checklist

Space: width, depth, height of the spot it goes.
Clearance: 3 in. sides, 3 in. top, 1 in. back for a countertop unit.
Door swing: can it open fully without hitting a wall, backsplash, or cabinet?
Interior: turntable diameter vs. your actual dinner plate.
Wattage: 900W or more.
Power: a grounded 120V outlet within reach, ideally on its own circuit.
If OTR: 30 in. above the cooktop, 30 in. cabinet width, and know your vent path.

Write the numbers down and bring a photo. It takes ten minutes and it’s the difference between a microwave that works and a microwave that goes back in the box.

Frequently asked questions

What size microwave do I need?

For everyday use, 0.9 to 1.2 cubic feet is the practical minimum, because that’s where the turntable gets big enough (around 11 to 12 inches) to actually rotate a standard dinner plate. Compact 0.7 cubic foot models suit mugs and small bowls but frustrate most households.

How much clearance does a microwave need?

A countertop model typically needs about 3 inches on each side, 3 inches above, and 1 inch behind for ventilation. Boxing one tightly into a cabinet restricts airflow, makes it run hot, and shortens its life. If you want it inside cabinetry, buy a built-in model or one with a manufacturer-approved trim kit.

Will a dinner plate fit in my microwave?

Check the turntable diameter, not the cubic feet. A standard dinner plate is 10.5 to 11 inches, so you want a turntable of at least 11 to 12 inches. Many compact microwaves have roughly 10-inch turntables, where a dinner plate won’t rotate and may not even lie flat.

How high should an over-the-range microwave be mounted?

Thirty inches from the cooktop surface to the bottom of the microwave, and at least 66 inches from the floor. That clearance is a fire-safety requirement, not a suggestion. If your cabinet won’t allow it, consider a low-profile OTR or a countertop unit with a proper range hood.

Can I put a countertop microwave inside a cabinet?

Not unless the manufacturer specifically supports it with an approved trim kit for that model. Countertop microwaves vent through their sides and top and need clearance. Enclosing one without proper airflow makes it overheat, which shortens its life and creates a fire risk.

What wattage microwave should I buy?

900 to 1,200 watts. That range cooks properly and matches most package instructions. Below about 800 watts, everything takes noticeably longer and heats less evenly, which is the usual complaint with cheap compact units.

Come see the difference for yourself

Home Star Appliances has served Houston since 2018 with new, scratch-and-dent, and quality-tested used refrigerators, washers, dryers, stoves, dishwashers, and microwaves, plus delivery, installation, parts, and financing. Come look at the units in person and ask us anything.

Visit us: 10216 Almeda Genoa Rd, Houston, TX 77075
Call: (713) 568-6088
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10216 Almeda Genoa Rd, Houston, TX 77075, United States

(713) 568-6088