Finding the right air filter for your home can be surprisingly confusing. Filters come in many different sizes, thicknesses, and MERV ratings, and choosing the wrong filter can result in a poor fit or an unsuitable level of filtration.
Your Own Consumer’s air filter guides help you identify the right replacement filter, understand filter sizes and MERV ratings, and make a more informed buying decision. Whether you’re replacing a 16x25x1, 20x20x1, 20x25x1, or another common HVAC filter, start with the size printed on your existing filter.
Whether you’re replacing a 16x25x1, 20x20x1, 20x25x1, or another common HVAC filter, start with the size printed on your existing filter and use our guides to find the right replacement.
Find Your Air Filter Size
The easiest way to find a replacement filter is usually to check the dimensions printed on your current filter.
Air-filter sizes are commonly written as:
Width × Height × Depth
For example:
20 × 25 × 1
Note that the dimensions printed on a filter are often nominal dimensions, so the actual physical dimensions may be slightly different. Check the manufacturer’s listed dimensions when an exact fit is important.
Popular Air Filter Sizes
Common residential air filter sizes include:
- 20x20x1 air filters
- 16x25x1 air filters
- 20x25x1 air filters
- 20x25x4 air filters
- 20x20x2 air filters
- 20x25x2 air filters
Air Filter Sizes
Air filters are available in many different nominal sizes. Some of the most common residential HVAC filter sizes include 1-inch, 2-inch, 4-inch and thicker filters.
If you’re unsure what size you need, don’t guess based only on the opening in your HVAC system.
Start by checking the existing filter.
Look for a size printed on the filter’s cardboard frame. You may see something similar to:
16 × 25 × 1
or
20 × 25 × 4
The printed dimensions are generally the easiest starting point when replacing an existing filter.
Our detailed air filter size guides will help you find the right replacement filter for common HVAC systems.
How Often Should You Replace an Air Filter?
There isn’t one replacement interval that works for every home.
How often you should replace a filter depends on factors such as:
- Filter thickness and design
- HVAC system usage
- Household occupancy
- Pets
- Indoor air conditions
- The filter’s condition
Instead of relying only on a calendar reminder, inspect the filter periodically and follow the replacement guidance provided by the filter manufacturer and your HVAC system manufacturer.
A visibly loaded or dirty filter may need attention sooner than a lightly used filter.
How to Choose the Right Replacement Filter
When buying a replacement filter, check these details before ordering:
1. Filter size
Match the size of your existing filter.
2. Filter thickness
A 1-inch filter and a 4-inch filter are not interchangeable simply because their width and height are the same.
3. MERV rating
Choose a filtration level appropriate for your HVAC system and household needs.
4. Actual fit
Nominal filter dimensions can differ slightly from the actual physical dimensions of the filter. When fit is critical, check the manufacturer’s actual dimensions.
5. Quantity
Filters are often sold in multipacks. Compare the price per filter rather than looking only at the total package price.
Need Help Finding Your Filter?
If you already know the dimensions of your current filter, start with the corresponding size guide.
If you don’t know the size, we’ll soon make it easier to identify your filter using our Filter Finder.
Our Filter Finder will be added here as the section develops.
Air Filter Resources
Our air filter guides will cover:
- Air filter sizes
- Furnace filter sizes
- HVAC filter sizes
- MERV ratings
- Filter replacement
- Choosing the right filter
- Common filter dimensions
- Filter compatibility
Our goal is simple: help you identify the filter you need without making the process unnecessarily complicated.
Frequently Asked Questions
Check your existing filter first. The size is often printed on the filter frame and is usually expressed as width × height × depth, such as 20 × 25 × 1.
No. Residential HVAC systems use many different filter dimensions and thicknesses. Always check the size required by your system before buying a replacement.
No. A higher MERV rating can provide greater filtration, but the filter also needs to be appropriate for your HVAC system. The system must be able to maintain adequate airflow with the filter installed.
It depends on the filter, HVAC system, household conditions, and usage. Inspect the filter regularly and follow the manufacturer’s recommendations rather than relying on one universal replacement interval.
Not necessarily. Filter thickness affects how the filter fits into the HVAC system and how air moves through it. Use the thickness specified for your system unless the manufacturer specifically allows another configuration.