How to Measure a Microwave | Get the Right Fit Every Time

To measure a microwave correctly, record the external width, height, and depth while accounting for mandatory clearance requirements like a 30-inch stove-to-microwave height and one inch of rear ventilation space.

Buying a new microwave seems simple until the one you picked doesn’t fit the cabinet, hits a wall when the door opens, or suffocates against the back panel. The fix is a ten-minute measurement session that anyone can do, and it saves a return trip and a restocking fee.

What You Need Before Measuring

A standard tape measure does the job. A laser measure speeds things up if you have one. Grab a pencil and paper or open a notes app — you’ll write down four numbers plus two clearance checks.

If you’re measuring an existing microwave that still works, unplug it and clear everything out of the interior before you start. For an over-the-range or built-in unit, you’ll measure the cabinet cutout instead of the appliance itself, since the hole determines what fits.

How to Measure a Microwave: The Four Dimensions That Matter

Take every measurement at the widest point, in inches, and round to the nearest eighth of an inch. The four numbers that decide whether a microwave fits are width, height, depth (door closed), and depth (door open).

Width

Measure horizontally across the widest part of the microwave’s exterior — usually the sides of the unit. For an over-the-range model, measure the cabinet cutout from one inner sidewall to the other. Standard OTR cutouts are 30 inches wide, but never assume; cabinets shift during installation and the actual opening can be off by half an inch.

Height

Measure vertically from the bottom of the microwave to the top. For OTR installation, the critical number isn’t the microwave’s own height — it’s the 30-inch clearance between the top of the stove and the bottom of the microwave. That gap is mandatory for safety and heat dissipation, and local building codes enforce it.

Depth (Door Closed)

Measure from the back of the microwave to the front of the door with the door fully closed. This is the measurement that tells you whether the unit will fit between your rear wall and counter edge. Countertop microwaves typically range from 14 to 20 inches deep when closed.

Depth (Door Open)

Open the door to a 90-degree angle and measure from the back of the microwave to the farthest point of the open door. An over-the-range microwave with the door open can extend 30 to 35 inches from the wall. If your countertop ends at 26 inches, that open door hangs unsupported and the microwave tilts forward when you pull a hot plate out.

Clearance Requirements (Skip These and You Regret It)

A microwave that fits dimensionally can still fail in real life if you ignore the breathing room and swing space it needs. These are the numbers that trip up most buyers:

• Rear ventilation: 1 inch minimum between the back of the microwave and the wall. Blocking this causes overheating and shortened lifespan.
• Side clearance: 6 inches on each side so the door swings fully open without hitting a cabinet or wall.
• Counter edge clearance: 3 inches between the front of the microwave and the counter edge so the door doesn’t hang off the edge of the cabinet when open.
• Distance from cooktop: 2 feet between the microwave and a gas or electric range to prevent heat damage to the appliance.

Standard Microwave Dimensions vs. Your Space

The table below shows typical dimensions by type. Use them as a shopping shortcut, but always confirm against your own measurements since brands differ slightly even within the same category.

The single most common mistake is assuming an over-the-range cutout is exactly 30 inches wide. Measure it. The second most common is forgetting that the plug needs access — a built-in installed flush against a rear wall with no outlet clearance can’t be plugged in without pulling the whole unit out.

Home Depot’s official measuring guide walks through each step with diagrams and covers the clearance rules that manufacturers expect you to follow.

What to Look For Before You Buy

Once you have your space measurements, match them against the microwave’s specs on three hidden details that most product pages bury in the fine print:

Venting Type

Over-the-range microwaves either duct air outside or recirculate it through a charcoal filter back into the kitchen. Check which kind your current setup uses before ordering. Switching from ducted to recirculating means cutting a cabinet hole or running new ductwork — a job that often needs a pro.

Handle Protrusion

Factory dimensions usually list depth without the handle. If the handle sticks out another two inches and you’re working with tight counter clearance, that open door plus handle might clear the edge by half an inch instead of the safe three.

Trim Kit Compatibility

Built-in microwaves often need a separate trim kit to fill the gap between the appliance and the cabinet opening. The kit adds width and height, so measure the cabinet opening a second time with the trim kit specs in hand.

Two Safety Numbers You Don’t Compromise On

Manufacturers and local codes agree on two hard limits. The 30-inch stove-to-microwave clearance is not a suggestion — it prevents heat from warping the microwave’s electronics and meets fire safety standards in every major US code. The 6-inch side clearance ensures the door opens fully so you can load and unload without reaching around a half-open door while holding something hot.

Checklist: Confirm Fit Before You Click Buy

Run through this sequence in order. If every box checks, the microwave goes in without surprises.

• Width of cutout or counter space measured at the narrowest point
• Height from countertop to bottom of upper cabinet (or stove to bottom of OTR opening)
• Depth with door closed, measured from rear wall to front of closed door
• Depth with door open, measured from rear wall to farthest point of open door
• 1-inch gap between microwave back and rear wall confirmed
• 6-inch clearance on each side of the microwave confirmed
• 3-inch clearance between counter edge and microwave front when door is closed
• 2-foot distance from microwave to cooktop or range confirmed
• Outlet accessible without blocking the microwave’s ventilation
• Venting type matches existing setup (ducted or recirculating)
• Trim kit accounted for if installing as a built-in

When the measurements pass and the clearance numbers line up, the installation takes an hour. When they don’t, the return takes two days and costs a fee. The tape measure is cheaper either way.