Air Filter Nominal vs Actual Sizes
Type the size printed on a filter, such as 16x25x1, or the size you measured, such as 15.5 x 24.5, to see the nominal and actual size side by side. No account, nothing to install.
Look up a filter size
The lookup box needs JavaScript. The full table is below.
| Nominal size (on the frame) | Actual size |
|---|---|
| 10x10x1" | 9.5" x 9.5" x 0.75" |
| 12x12x1" | 11.5" x 11.5" x 0.75" |
| 12x24x1" | 11.5" x 23.5" x 0.75" |
| 14x14x1" | 13.5" x 13.5" x 0.75" |
| 14x20x1" | 13.5" x 19.5" x 0.75" |
| 14x25x1" | 13.5" x 24.5" x 0.75" |
| 16x20x1" | 15.5" x 19.5" x 0.75" |
| 16x25x1" | 15.5" x 24.5" x 0.75" |
| 18x20x1" | 17.5" x 19.5" x 0.75" |
| 20x20x1" | 19.5" x 19.5" x 0.75" |
| 20x24x1" | 19.5" x 23.5" x 0.75" |
| 20x25x1" | 19.5" x 24.5" x 0.75" |
| 20x30x1" | 19.5" x 29.5" x 0.75" |
| 24x24x1" | 23.5" x 23.5" x 0.75" |
| 25x25x1" | 24.5" x 24.5" x 0.75" |
| 16x25x2" | 15.5" x 24.5" x 1.5" |
| 20x20x2" | 19.5" x 19.5" x 1.5" |
| 20x25x2" | 19.5" x 24.5" x 1.5" |
18 of 18 sizes shown.
Nominal and actual filter size
The size printed on a filter frame is its nominal size, a rounded number used to order it. The actual size is the real measurement. In this table every width and length is half an inch under nominal, a 1 inch filter is 0.75 inch thick and a 2 inch filter is 1.5 inches thick. Order by the nominal size; use the actual size when you are measuring a slot with a tape.
Frequently asked questions
What is the actual size of a 16x25x1 filter?
A 16x25x1 filter measures 15.5 by 24.5 by 0.75 inches. The size printed on the frame is the nominal size, a round number used for selling and ordering; the actual size is a little smaller so the filter slides into a slot cut for the nominal size.
What is the difference between nominal and actual filter size?
Nominal is the rounded size printed on the frame and used to order the filter. Actual is the real measurement. In the sizes in this table, every width and length is half an inch under nominal, a 1 inch filter is 0.75 inch thick and a 2 inch filter is 1.5 inches thick.
Which size do I use to buy a filter, nominal or actual?
Buy by the nominal size printed on the frame of the old filter, for example 20x25x1. If you measure the slot or the old filter with a tape and get 19.5 by 24.5, that is the actual size of a 20x25x1 filter, and the lookup above takes it too.
Does this table cover every filter size?
No. It lists the 18 common 1 inch and 2 inch sizes from the Tools Reference in the Equipment Tracker app. Other sizes, thicker filters and custom frames are not in it, so read the size printed on the frame of the filter you are replacing.
Does this page store my filter sizes or need an account?
No to both. The lookup runs in your browser and nothing is saved when you close the tab. If you want the filter size kept on each unit, so you know what to bring to the next filter change, that is what Equipment Tracker is for.
Keep filter sizes on each unit in Equipment Tracker
Write the filter size on the unit once and it is there on the next service call, on your phone, with or without signal. The core of the app is free on the phone, and every first plan, Pro or Team, starts with a 7-day free trial.
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