How to Measure?
Measuring guide
How to Measure for a Perfect Fit
Every register, grille, and diffuser on our site is listed by the size of the opening it covers, not the size of the metal faceplate. Measure the right thing and your order fits the first time.
The one ruleOrder by duct opening measurementsMeasure in under a minute
1
Remove your old register
Unscrew or lift out the existing unit so you can see the open hole in the wall, ceiling, or floor.
2
Measure the opening
Measure the hole itself: width first, then height (for example 4"W x 10"H). Round to the nearest standard size.
3
Order that size
Pick the product listed in that size. The faceplate is sized to overlap the opening and screw holes on every side.
Do
- Measure the duct opening (the hole)
- Put width first: 4"W x 10"H and 10"W x 4"H are different products
- Check each opening separately; rooms often mix sizes
Don't
- Don't measure the old faceplate: it is 1" to 2" larger than the opening
- Don't measure over the old register while it is still installed
- Don't assume all vents in your home are the same size
What to measure for each product
The duct-opening rule covers most products. A few categories are measured a little differently; here is the complete list.
Supply registers and return grilles (wall & ceiling)
Measure the duct opening, width x height. The listed size is the opening; the steel or aluminum faceplate overlaps it on all sides.
Order size = duct openingFloor registers
Measure the hole in the floor, width x height. Floor registers drop into the opening and rest on the flange; no screws needed for most models.
Order size = floor openingReturn air filter grilles
Order by the filter size you use (which matches the duct opening). A filter grille listed 20"x20" holds a standard 20"x20" filter. Note: a filter's actual size is about 1/2" smaller than its listed (nominal) size, so a 20"x20" filter measures about 19-1/2"x19-1/2". That is normal and it still fits.
Order size = filter sizeRound diffusers
Measure the diameter of the round duct (neck) the diffuser connects to, for example 6", 8", or 10". The visible outer cone is larger than the neck.
Order size = neck diameterT-bar / drop ceiling diffusers
Made for a standard 24"x24" ceiling grid. Nominal size is 24"x24"; the actual panel is slightly smaller (about 23-3/4") so it drops into the grid. Choose by the neck size of your duct (6" to 14").
Fits 24x24 grid + match neck sizeBaseboard return grilles
Standard baseboard returns follow the duct-opening rule. Corner and wooden baseboard models are the exception: they are sold by their overall (outer) length, for example 48", because they cover the wall joint rather than a cut opening.
Corner / wooden = outer lengthToe kick grilles
For under-cabinet openings: measure the duct opening in the cabinet toe kick, width x height, just like a wall register.
Order size = duct openingExterior louvers
Measure the duct or pipe opening the louver vents, just like an interior register. Louvered blades and screen sit in a frame that overlaps the opening.
Order size = duct openingPlease note: exact outer dimensions vary by model and are shown on every product page under "Outer Dimensions", and again at checkout. If your space is tight (between joists, inside trim), check that the faceplate fits before ordering.
Common questions
My opening is between two standard sizes. Which do I order?
Order the size that matches the duct behind the wall, not the drywall cut. If the cut is ragged or oversized, the faceplate usually still covers it since it overlaps 1" to 2". Not sure? Send us the measurements and a photo and we will confirm the right size.
Does the first number mean width or height?
Width first, always. A 12"W x 6"H register has slots running along the 12" side. If your opening is taller than it is wide, order the reversed size (6"W x 12"H) instead.
Will the new register cover my old screw holes and paint lines?
In most cases yes. Faceplates overlap the opening on every side, which covers typical screw holes and paint edges left by the old register. Compare our "Outer Dimensions" with your old faceplate if you want to be certain.
What is airflow direction and do I need to match it?
Supply registers come in 1-way, 2-way, 3-way, and 4-way air deflection. Pick based on where you want air directed (for example, a register above a window often uses 1-way aimed into the room). It does not affect the size you order.
I ordered the faceplate size by mistake. What now?
It happens. Reply to your order email or contact us and we will help you exchange it for the correct duct-opening size.
Got your measurements? Find your size.
Use the size finder at the top of any page, or browse the category and filter by width and height.
Shop by size Ask us first- Choosing a selection results in a full page refresh.