What size air filter do I need?

Type the numbers printed on the edge of your old furnace or AC filter. We'll show the typical actual size and help you pick a filtration level.

Length
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Common sizes:More sizes →
No filter handy? The size is usually printed on the frame. See how to find your filter size.

16 × 25 × 1 filter Common size

Nominal size (what's on the label)16 × 25 × 1 in
Actual size (typical)about 15½ × 24½ × ¾ in
Filters are sold by a rounded "nominal" size. The real frame is usually about ¼ to ½ inch smaller so it slides into the slot. Shop by the nominal size on your old filter. Exact dimensions vary by brand. Why?

Pick a filtration level (MERV)

MERV 8

Good everyday choice. Catches dust, lint and pollen. Easy on airflow.

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MERV 11

A step up for pets and allergies. Traps more fine dust and pet dander.

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MERV 13

Most filtration for typical homes. Can restrict airflow in some systems, so check your HVAC manual first.

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Disclosure: we may earn a commission if you buy through links on this page, at no extra cost to you. Read our affiliate disclosure.
Not sure which to choose? Read MERV 8 vs. 11 vs. 13.

Remind me to change it

Coming soon: a free email reminder when it's time. Many 1-inch filters need replacing every 1–3 months. This form doesn't send or store anything yet.

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Popular guides

How to find your air filter sizeRead the label, measure the old filter, or measure the slot.Nominal vs. actual air filter sizeWhy a 16x25x1 filter isn't really 16 by 25 by 1.MERV 8 vs. 11 vs. 13: which should you buy?A plain-English way to pick a filtration level.How often should you change your air filter?A simple schedule, and when to change it sooner.Common air filter sizesA reference table of common 1-inch sizes, 10x20 to 25x25.

Common questions

Why is my filter smaller than the size printed on it?

The printed size is the "nominal" size, rounded for easy shopping. The actual frame is usually about ¼ to ½ inch smaller so it fits the slot. Buy the nominal size shown on your old filter.

How often should I change my furnace or AC filter?

A common guideline for 1-inch filters is every 1–3 months, and more often with pets, allergies, or heavy use. Thicker media filters usually last longer, so follow the filter maker's guidance.

Which MERV rating should I buy?

MERV 8 suits most homes. MERV 11 is a good step up for pets or allergies. MERV 13 filters the most but can reduce airflow in some systems, so check your HVAC manual or ask a technician first.