What Size Air Filter Do I Need? A Complete Air Filter Size Chart

Find the Best Air Conditioner and Furnace Filter Sizes with Nominal Size, Actual Size, and MERV Ratings

Listed in the chart below are the standard size 1 inch, 2 inch and 4 inch depth air conditioner filters for your AC, Furnace, HVAC at Atomic Filters. Also listed are the whole house air filters collections carried by Atomic Filters.

Find Your Furnace Filter by Size or Brand

In addition to carrying major brands of furnace filters like Lennox, Carrier, Trion Air Bear and Skuttle we also offer custom size filters at Atomic. Select the size to see a collection of filter for that size or select your Brand and see the entire collection of Whole-house furnace filters available. Need to know more about MERV ratings check out our air filterknowledge page. Filter are usually listed by the Nominal Size which is a rounded number, based off of the true dimensions of the filter which are called the "actual size". 

What Size Air Filter Do I Need?

Using the right size AC filter is essential to maintaining good indoor air quality and ensuring your HVAC system runs efficiently. Here's how to find the right size:

• Check the existing filter: Look for the dimensions printed on the frame of your current filter, usually in the format of length x width x depth (e.g., 20x20x1) which is known as a nominal size (This is the size used to label the filter). The nominal size can be rounded up or down depending on the brand. Actual sizes of a filter with the same nominal size can vary from one manufacturer to another. For instance, a 16x25x5 filter from one manufacturer may have a completely different actual size than another manufacturer. Check to see if the actual size is also on the filter. These are the actual dimensions of the filter and sometimes listed right under the nominal size.

• Measure the filter: Confirm the actual size of the filter by measuring. If the size isn't printed, measure the length, width, and thickness of the filter with a tape measure or ruler. Search for the filter by the actual size. 
• Measure the filter slot: If you don't have a filter to reference, measure the inside of the filter slot in your HVAC unit. Subtract 0.25" to 0.5" from each dimension to find the size that will fit snugly.
• Check your HVAC manual: The manual may specify the appropriate filter size for your unit. Search the model number to see what the nominal or actual sizes are of the correct filter.  

Common air conditioner filter sizes include 10x20x1, 14x20x1, 16x24x1, 18x30x1, 20x20x1, 16x25x1, and 20x25x1. However, you should always measure or check your manual to ensure you get the correct size for your system. Once you know the right size, you can use the air filter size chart on this page to find the right replacement filter.

Nominal vs. Actual AC Filter Sizes

When replacing your HVAC system's air filter, you'll encounter both nominal and actual filter sizes. Nominal size refers to the standardized, rounded dimensions used for packaging and labeling, usually in whole numbers like 16x20x1. 

Actual size represents the filter's precise measurements, typically slightly smaller than the nominal size. For example, a 16x20x1 nominal size filter may actually measure 15.5x19.5x0.75 inches.

It's important to note that the differences between nominal size and actual sizes can vary between manufacturers, so be sure to use our size chart to find the right filter. A filter that's too large or small can allow air to bypass it, reducing filtration efficiency. 

A Quick Guide to AC Filter MERV Ratings

MERV, which stands for Minimum Efficiency Reporting Value, is a rating system that measures the effectiveness of air filters. MERV ratings range from 1 to 16, with higher numbers indicating better filtration.

Here's a quick breakdown of what the different MERV ratings mean:

• MERV 1-4:These filters offer minimal filtration and are typically used in residential window AC units. They can capture large particles like pollen, dust mites, and carpet fibers.
• MERV 5-8: Filters in this range are commonly used in residential and commercial settings. They can trap particles like mold spores and some dust particles.
• MERV 9-12:These filters offer superior filtration, especially for those with allergies or sensitivities to airborne particles. They can capture very fine particles, including pet dander.
• MERV 13-16: Filters with these ratings can trap bacteria, smoke, and other tiny particles. They are excellent for homes where occupants suffer from severe allergies or respiratory issues.

Filters with aMERV 11 orMERV 13 rating are suitable for most homes, offering a good balance between filtration and airflow. If you or your family members suffer from allergies, asthma, or other respiratory sensitivities, opting for a filter with a MERV rating of 13 can significantly improve your indoor air quality by trapping more allergens and irritants.

Learn more about thedifference between MERV 11 and MERV 13 air filters. 

How Often Should I Change My AC Filter?

The general recommendation is to change 1-inch air filters every 60-90 days. 2-inch and 4-inch filters may last up to six months or longer before they need changing. However, there are several factors that can influence this timeline:

• If you have pets, you should change your filter every 60 days or 2 months due to pet hair and dander
• For homes with multiple pets or people with allergies or respiratory conditions, change your filter every 20-45 days.
• Vacation or vacant homes that don't see much use can wait 9-12 months between filter changes.
• If you live in a dusty area or have recently done home renovations, you may need to change your filter more frequently, around every 30-60 days.
• Cheaper fiberglass filters need to be changed every 30 days, while higher-quality pleated filters can last up to 90 days.

The best approach is to visually inspect your filter every month. If it looks dirty, dusty, or clogged, go ahead and change it even if the recommended timeframe hasn't passed yet

The Impact of Buying the Wrong Air Filter Sizes

Using the wrong size air filter in your HVAC system can lead to various issues. A filter that's too small allows pollutants to circulate, worsening allergies and respiratory problems. An oversized filter may leave gaps for unfiltered air to enter.

Incorrectly sized filters can restrict airflow, making your HVAC work harder to maintain the desired temperature, reducing efficiency, increasing energy bills, and causing uneven temperatures. The added strain on components can lead to premature failures and costly repairs. In some cases, using the wrong filter size may also void your HVAC warranty, as manufacturers specify appropriate sizes and consider deviations improper maintenance.

To avoid these problems and ensure optimal performance, consult your system's manual, measure your current filter, and use our air filter size chart to find the right replacement filter.

Find Your Filter by Brand

Click the link for the brand to see the entire collection. Use the search to find your item by Model, Title or Size. See the complete expanded list of filters by Brand Size and actual size.

Find Your Furnace Filter by Size