Air Filter Sizes Chart 2025 | Find Your Exact Size

 

 

How to Measure Your Air Filter - AC Filter Size Chart

Understanding HVAC filter measurements - Air filters have two sizes you need to know:

• Nominal Size: The rounded size printed on the filter label (like 20x20x1)
• Actual Size: The exact measurements (like 19.5x19.5x0.75)

Most Popular Furnace Filter Sizes (September 2025)

Based on thousands of orders, these are our top-selling HVAC filter sizes:

Complete Air Filter Sizes Chart - All Furnace Filter Dimensions Available

Click any size below to shop filters with that dimension. All sizes available in MERV 8, MERV 11, and MERV 13 ratings. Learn more about choosing the right MERV rating for your needs.

Standard 1-Inch Filter Sizes

Thicker Filter Options

Need a thicker filter? We carry these depths:

• 2-Inch Air Filters - Extended life, better filtration
• 4-Inch Air Filters - Maximum filtration, longest lasting
• 5-Inch Air Filters - Premium whole-house filtration

Understanding Nominal vs Actual Filter Dimensions - HVAC Filter Measurements

The size printed on your filter (nominal) is typically rounded up from the actual measurements. Here are common examples of furnace filter dimensions:

Nominal Size (Label Size)	Actual Size (True Dimensions)	Shop This Size
20x20x1	19.5 x 19.5 x 0.75	Shop 20x20x1 →
16x25x1	15.5 x 24.5 x 0.75	Shop 16x25x1 →
20x25x1	19.5 x 24.5 x 0.75	Shop 20x25x1 →
16x20x1	15.5 x 19.5 x 0.75	Shop 16x20x1 →
20x30x1	19.75 x 29.75 x 0.75	Shop 20x30x1 →

Filter Sizes by HVAC Brand

Looking for filters for your specific HVAC system? We carry replacement filters for all major brands:

• Lennox Filter Sizes - Complete guide with model numbers
• Carrier, Trane, Rheem, Goodman - Use our standard size chart above for 1 inch filters. Use Complete list Chart for whole house filters.
• Custom Sizes Available - Contact us for hard-to-find dimensions

Frequently Asked Questions About Air Filter Sizes

What's the difference between nominal and actual filter size?

Nominal size is the rounded size printed on the filter label (like 20x20x1), while actual size is the exact measurement (like 19.5x19.5x0.75). Always order by the nominal size unless specifically instructed otherwise.

What if my filter size is too big?

An oversized filter won't fit properly and may damage when forcing it in. This creates gaps that allow unfiltered air to bypass the filter, reducing your indoor air quality. Always choose the correct size or go one size smaller if needed.

What if my filter is too small?

Undersized filters leave gaps around the edges, allowing dust and allergens into your HVAC system. They also clog faster due to reduced surface area, making your system work harder and increasing energy costs.

How do I find my filter size without an old filter?

Check these locations:

1. Look for a size printed on the filter slot or door
2. Measure the filter opening and round up to the nearest inch
3. Check your HVAC system manual or model number online
4. Contact us with your HVAC model - we'll help you find the right size

Can I use a different brand filter if the nominal size matches?

Yes, in most cases. However, actual dimensions can vary slightly between manufacturers. Our Atomic Filters are designed to match industry-standard actual sizes for each nominal size, ensuring compatibility with your system.

How often should I change my furnace filter?

For standard 1-inch filters, change every 30-90 days depending on usage, pets, and allergies. Thicker filters (2-inch or 4-inch) can last 3-6 months. Check monthly and replace when visibly dirty or when airflow seems restricted.

Video: How to Find the Right Replacement Filter

Watch this quick guide to learn how to find your filter size and avoid common mistakes:

Helpful Resources

• MERV 8 vs MERV 11: Which Filter Is Right for You?
• How to Choose the Right Air Filter Every Time
• Complete List of Filter Sizes with MERV Ratings
• Replacement Air Purifier Filters