Sizing guide
How to find your air filter size
Your filter size is printed on the cardboard edge of your existing filter. If that's not available, you can measure the slot directly. Either way takes under a minute.
Check the cardboard edge of your current filter. You'll see a size like 16x20x1 — that's width × height × depth. Order that exact size.
Method 1 — Read your existing filter (fastest)
Pull out your current filter and look at the cardboard frame. The size is printed on one of the long edges. It reads like 16x20x1 or 20x25x4. That three-number format is Width × Height × Depth, all in inches. This is the nominal size — what you order.
Write it down and use the size finder to see pricing.
Method 2 — Measure the slot
If the label is worn or you don't have the old filter, measure the filter slot opening — not the filter itself.
Nominal vs actual size
Every filter has two sizes. The nominal size (what's printed on the frame, rounded up) is what you order. The actual size is the true physical measurement, typically 0.25–0.5 inches smaller in each dimension.
Example: a filter labeled 16x20x1 has an actual size of 15.5" × 19.5" × 0.75". Always order by nominal size — all brands use the same rounding convention.
Ready to find your filter?
Enter your dimensions and see pricing across all pack sizes.
Use the size finder →Frequently asked questions
Where is the air filter size printed?
On the cardboard edge of your current filter — it reads like "16x20x1". Check all four long edges if you can't find it immediately.
What if my size is not standard?
Non-standard sizes exist — especially in older homes. You can order a custom-cut filter to your exact dimensions. See our custom size page for details.
What is the difference between nominal and actual filter size?
Nominal size is the rounded number printed on the filter (e.g. 16x20x1). Actual size is the true physical measurement, typically 0.25-0.5 inches smaller. Always order by nominal size.
Can I use a filter that is slightly smaller than my slot?
No. A filter smaller than its slot leaves gaps that allow unfiltered air to bypass the filter entirely, pulling dust directly into your HVAC system. Always match the nominal size exactly.