How to Measure a Floor Register, Plus the Full Size Chart
Nine out of ten sizing mistakes come from one error, measuring the old vent cover instead of the hole it sits in. This guide shows the right way to measure in under two minutes, then links every standard size we stock so you can go straight to the right register.
The one rule: measure the duct opening, not the old cover
Register sizes describe the duct opening in your floor. A 4x10 floor register fits a hole that measures 4 inches by 10 inches. The old cover's faceplate is always bigger than the hole, so measuring it will send you a size up and the new vent will not fit.
Here is that difference as a real number. On our Classic line the faceplate adds 0.78 inches overall, so the 4x10 register that fits a 4 by 10 opening has a faceplate measuring 4.78 by 10.78 inches. Measure the faceplate instead of the hole and you will read something close to 5 by 11, order the wrong size, and end up returning it.
Measuring in three steps
1. Lift out the old vent. Most drop-in vents lift straight out. If it's screwed down, remove the screws first.
2. Measure the hole. Width and length of the opening in inches, to the nearest eighth. Measure in two spots per direction, old openings are rarely perfectly square, use the smaller reading.
3. Order that size. A 4x10 opening takes a 4x10 register. Our drop-in design sits flush into the opening, no screws, no adhesive.
Special situations
Rough or oversized cut around the hole? Our LuxeEdge line uses a wider flange that hides damaged edges and gaps.
Joist blocking one side? Our Joist Avoider models offset the drop-in box so the vent still sits centered. Send us a photo and we'll confirm the right one.
Something in the way below the opening? A drop-in register needs a little clear depth under the floor surface for the box to sit into. If there is a damper, a cable or a duct elbow immediately below, send a photo down the opening and we will tell you what will clear it.
Wall and ceiling vents measure the same way, the hole in the drywall, not the old grille. Our two-part wall vents clamp into the opening with no visible fasteners.
Between sizes or an odd opening? We build custom size vents to any dimension in our Mississauga shop.
Floor register size chart
Every size below is stocked in our Classic flush drop-in line. The size is the duct opening it fits.
| Opening width | Stocked lengths |
|---|---|
| 2 inch | 2x10, 2x12, 2x14 |
| 3 inch | 3x10, 3x12, 3x14 |
| 4 inch | 4x8, 4x10, 4x11, 4x12, 4x14, 4x16, 4x20, 4x24, 4x30, 4x36, 4x48, and every inch in between up to 4x72 |
| 5 inch | 5x10, 5x12, 5x14 |
| 6 inch | 6x6, 6x8, 6x10, 6x12, 6x14, 6x20, 6x24, 6x30 |
| 8 inch | 8x8, 8x10, 8x12, 8x14, 8x20, 8x24, 8x30 |
| 10 inch | 10x10, 10x14, 10x24, 10x30 |
| 12 inch | 12x12, 12x16, 12x20 |
Half sizes and in-between lengths are stocked too, browse the full floor vent collection or search your exact size. If your measurement isn't listed anywhere, that's what our custom size program is for.
If your measurement isn't on the chart
That is normal rather than unlucky. About 36% of our revenue comes from sizes outside our fifty best sellers, because older houses, additions and previous renovations rarely produced round numbers. Openings we have built for include 6x9.5, 3.5x20.5, 5.5x23.5, 4x50.25 and 6x71.
We work to a tolerance of plus or minus 1/32 inch and build to any size up to 24 by 72 inches, so a made-to-order vent fits the opening you actually measured. Forcing the nearest stock size instead leaves a gap, or a cover that rocks underfoot, and on a cold air return a gap at the frame pulls unfiltered air straight out of the wall cavity.
One exception worth knowing before you choose a model. Our seamless Breeze and ON models use a laser welded top plate made in fixed tooling, so those two come in listed sizes only. If your opening is not standard, Classic is the drop-in we build to your dimensions.
Common questions
My opening is 4 1/8 x 10. Do I order 4x10? Yes if the extra eighth is on one rough edge, our vents allow a little play and LuxeEdge covers more. If it's a true 4.25 or larger, go custom.
The old cover says 4x10 on the back. Can I trust it? Usually, but measure the hole anyway. Thirty seconds now beats a return shipment later.
How long will it take to arrive? Stocked sizes in black or white ship fast, and over 93% of our in-stock orders leave the same or next business day. Custom sizes, and grey or silver finishes, are made to order in 3 to 4 weeks.
Do wall return grilles size the same way? Yes, by the wall opening. Common return sizes like 6x24, 8x30 and larger are in the wall vent collection. If it is a return rather than a supply, size matters more than you would expect, and how to size a return air grille explains why.
One more trick: match your floor
Once the size is right, you can make the vent almost disappear. Our floor matching designs accept a piece of your own flooring in the vent face.
