Three measurements, in inches.
The size on the box isn’t the size on your tape measure. That’s normal.
Filters are sold by a rounded, standard size called the nominal size. The filter itself is built slightly smaller so it slides into its slot easily.
Nominal size
The rounded size printed on the filter’s frame and box, like 20 × 25 × 1. It’s the size you shop by, and the size every filter in our store is listed under.
Actual size
The filter’s real outside dimensions. Usually about ½" smaller in length and width, and a 1" filter is typically about ¾" deep. A 20 × 25 × 1 measures about 19½ × 24½ × ¾.
How we list our filters
Every product and size option uses the nominal size. The exact dimensions are listed under Specifications on the product page, so you can check them against your measurements.
Measured your old filter and got something like 19½ × 24½ × ¾? Round each number up to the next whole inch to get the nominal size: 20 × 25 × 1. If your measurements don’t round to a standard size, we can build a filter to your exact dimensions.
Can’t measure right now? Your size is probably written down somewhere.
Before you reach for the tape measure, check these places.
On the filter frame
Most filters have the nominal size printed on the edge of the frame, often with the brand and MERV rating. Check the old filter before you throw it out.
On your unit’s nameplate
Furnaces, air handlers, HRVs and air exchangers carry a label with the manufacturer, model number and serial number. It’s usually inside the access door or on the side of the cabinet.
In the owner’s manual
The manual lists the filter size and type for your model. Lost it? The model number from the nameplate is usually enough to find it online, or for us to look it up.
Still not sure?
Send us a photo of the filter’s label or your unit’s nameplate, and our team will identify the right filter for you.
Sizing questions
What people ask us most about filter sizes. Don’t see yours? Give us a call.
My measurements fall between two sizes. Which do I order?
Round each measurement up to the next whole inch. Filters are built slightly under their nominal size, so a filter measuring 15½ × 24½ × ¾ is a 16 × 25 × 1. If rounding up doesn’t give you a size that exists, send us a photo or your measurements and we’ll confirm the right one.
There’s no size printed on my filter. What do I do?
Measure the old filter’s frame: length, width and depth, in inches, then round each up to the next whole inch. No old filter either? Measure the slot it slides into, or find the model number on your unit’s nameplate and send it to us.
My filter slot measures exactly 20 × 25. Will a 20 × 25 × 1 filter fit?
Yes. A 20 × 25 × 1 filter’s actual size is about ½" smaller in length and width, so it slides into a 20 × 25 opening with a little room to spare. That’s normal and by design.
Can you make a filter in a non-standard size?
Yes. If your measurements don’t round to a standard size, we build filters to your exact dimensions. Use the custom-size calculator on our residential page to price it, or contact us with your measurements.