How to Measure for a Recessed Bathroom Medicine Cabinet? | Fit The Opening

Measuring for a recessed medicine cabinet starts with the wall opening you can actually cut, not the cabinet’s visible face.

Getting the measurement right is the difference between a flush, professional install and a gap-riddled mess. The trick most people miss: the rough opening—the hole you cut in the drywall—is always smaller than the cabinet’s outer dimensions. The cabinet’s trim flange is what covers the extra space. Measure that opening correctly and the cabinet drops in clean.

What You Need To Measure Before Buying

You need five numbers before you shop, and the first one decides everything else. Measure the actual wall cavity, not the old cabinet you’re replacing.

• Opening width: the horizontal gap between the studs where the cabinet will sit.
• Opening height: the vertical space available, usually between the countertop and ceiling.
• Wall depth: the true cavity depth inside the studs—critical for deeper cabinets.
• Stud location: whether the cabinet can fit between existing studs or needs new framing.
• Clearance: room for the flange and the door swing, plus clearance above a faucet and below the ceiling.

Confirm the cabinet fits between your studs first; if it’s wider than the stud gap, you’re looking at structural modification on a non-load-bearing wall.

The Exact Rough Opening Formula

The rough opening is smaller than the cabinet. For two or more cabinets side by side, the opening width equals the combined widths minus 3/4 inch.

Those fractions matter. The extra 3/4 inch horizontally and 5/8 inch vertically is what lets the cabinet body slide into the hole while the outer flange covers the cut edge. Here’s the catch: that formula works only when the opening is truly square. The top and bottom lengths of the opening must match exactly before you cut and block, or the cabinet will sit crooked.

That depth is the trap—a standard 2×4 wall cavity is only about 3.5 inches deep, so a 4.92-inch cabinet will not fit without furring out the wall or another modification.

How To Install The Cabinet In The Opening

Once the hole is cut, the install takes patience more than skill. Confirm the hinge orientation for left-hand or right-hand operation before you lift the cabinet into place.

Insert the cabinet into the wall opening in a plumb, centered position. Level it with shims if needed, then secure it through the mounting holes. Confirm the cabinet sits flush with the drywall front edge, and add furring if the cabinet is deeper than the wall cavity.

Fully recessed installations require the flange to cover the rough opening evenly all around. For semi-recessed applications, the mirror edges should align with the wall surface.

If you’re still deciding which model to buy, our tested roundup of the best recessed bathroom medicine cabinets compares the top options on the market.

Common Measuring Mistakes To Avoid

Four mistakes ruin more installs than anything else. Cutting without checking the actual cabinet dimensions tops the list—the box dimensions on the listing may not match the unit you received. Failing to account for flange and trim coverage is next; the flange needs to overlap the opening evenly. Ignoring wall depth is the third, and skipping level and plumb checks is the fourth. Verify stud and hinge orientation before you cut, not after. You can’t force a cabinet into an undersized opening without damaging the drywall or the unit.