Measure an AC cover by its width, depth, and height: width across the side without wires, depth across the side with them, and height from the ground up. Size up if the exact match doesn’t exist.
Getting the measurements wrong means a cover that flaps, traps moisture, or won’t go on. Whether covering a window unit for winter or a central condenser for the off-season, the same three dimensions apply: width, depth, and height. One wrong number is the difference between a snug fit and a return label.
Understanding the Three Key Dimensions
You need three numbers, each tied to a specific side of the unit. Mixing them up is the most common sizing error, so take these one at a time.
- Width: Measure across the side of the unit that has no wiring or piping. This cleanest surface gives you the true span.
- Depth: Measure across the side with wiring and piping. That side needs an opening or fasteners on the cover, so its exact width is critical.
- Height: Measure from the ground to the top of the air conditioner. For a window unit, this is the full vertical dimension of the chassis, not just the visible front.
Don’t forget protrusions. Wiring, piping, support brackets, and ground feet add to the real dimensions. A cover sized to the main body will pinch those extras, so include them in your width and depth numbers.
Window Unit vs. Outdoor Unit Sizing
The measuring logic is the same, but fit rules differ. A window unit sits partially inside the house, so the cover only fits the exterior portion; an outdoor condenser stands free, needing full clearance on every side.
As long as your unit sits at or below every maximum, it fits; if you’re over on any one, move up a size.
For central AC condensers, sizes jump considerably.
Vent and Register Covers Measure Differently
If you’re replacing a vent or register cover, the method changes completely. Don’t measure the faceplate you see; measure the duct opening behind it. The faceplate is almost always larger than the hole it covers. Measure the actual opening in the wall or floor, then buy a cover matching that opening, choosing one size up for a slightly loose fit.
Handling Custom Sizing and Odd Fits
When your unit doesn’t match a standard size, you have two options: size up or go custom. Most manufacturers advise the former. Sizing up slightly gives slack for the cover to settle without straining fabric or zippers—a slightly larger fit beats a smaller one every time, since the cover sits over the top rather than shrink-wrapping the compressor.
Always double-check the manufacturer’s size chart against your numbers before ordering, since manual variation is common and photos often show the intended fit.
Once you’ve got your numbers, match them against product specs; if you’re looking for options built for common condenser sizes, our roundup of the best outdoor AC covers lists tested models with dimensions.
When you’re ready to buy, keep your three numbers handy. Every product page lists dimensions in the same order—width x depth x height. Match all three, and you’ll get a cover that goes on in minutes and stays put. For vent covers, your single opening measurement is all you need.
FAQs
Should I size up or down if my AC is between cover sizes?
What happens if I measure the faceplate of a vent cover?
You’ll buy a cover that’s too large. The faceplate is always wider than the duct opening, sometimes by a couple of inches per side. Always measure the rough opening in the wall or floor, not the decorative trim—that determines which vent cover size you need.
Do I measure the ground feet on my outdoor AC unit?
Yes. The feet are part of the total height and depth; a cover sized to the chassis alone will ride up, leaving the bottom exposed to moisture and debris. Measure from the floor the unit sits on, including feet, to the highest point of the top casing.