Measure the duct opening, not the old cover. Two measurements, short side then long side, and you’ll know your exact vent size.
Vent covers are sized by the duct opening, the hole in the wall, ceiling or floor, not by the cover sitting on top of it. A “4×10” cover fits a 4″ × 10″ opening; the cover itself is bigger so it can overlap the edges.
Measured openings are rarely exact. Anything within about ¼″ of a standard size counts as that size, so an opening that measures 3⅞″ × 12⅛″ is a 4×12.
| Size | Duct opening (in) | Duct opening (cm) |
|---|---|---|
| 3×10 | 3″ × 10″ | 7.6 × 25.4 |
| 4×10 | 4″ × 10″ | 10.2 × 25.4 |
| 4×12 | 4″ × 12″ | 10.2 × 30.5 |
| 4×14 | 4″ × 14″ | 10.2 × 35.6 |
| 5×50 | 5″ × 50″ | 12.7 × 127.0 |
| 6×10 | 6″ × 10″ | 15.2 × 25.4 |
| 6×12 | 6″ × 12″ | 15.2 × 30.5 |
| 6×14 | 6″ × 14″ | 15.2 × 35.6 |
| 8×8 | 8″ × 8″ | 20.3 × 20.3 |
| 8×12 | 8″ × 12″ | 20.3 × 30.5 |
| 8×14 | 8″ × 14″ | 20.3 × 35.6 |
| 10×10 | 10″ × 10″ | 25.4 × 25.4 |
| 12×12 | 12″ × 12″ | 30.5 × 30.5 |
| 24×24 | 24″ × 24″ | 61.0 × 61.0 |
No. Sizes mean the same thing on every surface. What changes is the cover: floor vents are built to be stepped on, while wall and ceiling vents usually share the same openings and mounting. Not sure which style you need? Use the vent finder.
Measure the hole. Vent covers are sold by the size of the duct opening they fit, not the size of the cover itself. A 4×10 vent cover fits a 4″ × 10″ opening, and its faceplate is larger so it overlaps the edges.
Sizes are written short side first, then long side. A 4×12 opening is 4 inches across the narrow side and 12 inches along the long side.
Duct openings are rarely exact. A measurement within about ¼ inch of a standard size is that size, so 3⅞″ and 4⅛″ are both a 4″ side. If you are more than about ½ inch away from any standard size, the opening is probably non-standard and a standard cover may not sit right.
Round ducts are measured by diameter. Rectangular vent covers need a rectangular opening, so a round duct usually needs a boot or adapter that transitions it to a standard rectangular size first.
The sizing system is the same everywhere, so a 4×10 means a 4″ × 10″ opening on any surface. Floors usually use narrower openings such as 2×10 through 4×14, while walls and ceilings often use larger ones.
Fittes doesn’t make custom sizes. If none of the standard sizes fit, reach out to our support team. We often have new sizes in the pipeline, and when there’s enough demand for a size, we add it.
Still not sure? Contact our team with your measurements and a photo of the opening.