Reading Air Filter Labels: Size, Media and Frame Details Explained

Air filter labels can look straightforward at first glance, but the small print is often what decides whether a filter actually fits and performs as intended. If you are comparing products for a home, plant room or commercial site, knowing how to read the label can save time and reduce ordering mistakes.

This guide breaks down the most common label fields you will see on replacement filters, and explains what matters when you are checking compatibility with existing equipment.

Why the label matters before you order

A filter can appear to be the right shape in a product photo and still be the wrong fit on site. The label usually tells you the key details needed to compare one product line with another.

Look for:

• •Nominal or actual size
• •Filter media type
• •Frame or construction material
• •Airflow direction or orientation notes
• •Efficiency or rating information
• •Any special fitting notes, such as gasketed, pocket, pleated or panel style

If you are replacing an existing filter, the label is only one part of the check. It is still worth measuring the actual filter opening or the old filter itself. If you are not sure how to measure correctly, see how to measure an air filter.

Understanding filter size on the label

Size is the first detail most buyers check, but it can also be the easiest to misread. Labels may show a nominal size, an exact size, or both.

Nominal size versus actual size

Nominal size is a rounded or market-facing size used for ordering. Actual size is the precise physical dimension of the filter.

That difference matters because two filters with the same nominal label can still have slightly different actual dimensions depending on the manufacturer and product line. When comparing options, check all three dimensions where listed:

• •Length
• •Width
• •Depth or thickness

A label might show the size in millimetres, inches, or both. Australian buyers often see imperial sizes in older systems and metric sizes in newer equipment, so do not assume the format will be the same across all brands.

What to check on site

Before ordering, confirm:

• •The filter slot or frame opening size
• •Whether the filter slides in from the side, front or rear
• •Whether the depth is limited by door clearance or rails
• •Whether there is room for a thicker filter if the system allows it

If you are ordering for a commercial or industrial site, the mechanical services engineer or building owner should confirm the site requirement, especially where the filter is part of a designed ventilation arrangement. AS 1668.2:2024 may be relevant to the ventilation design, but site requirements should always be checked for the specific installation.

Reading media details without confusion

The media is the part of the filter that captures particles. Labels may describe it in different ways, and those descriptions are not always interchangeable.

Common media descriptions

You may see terms such as:

• •Synthetic media
• •Glass fibre media
• •Pleated media
• •Moulded or bonded media
• •Carbon media
• •HEPA media

Each media type has different airflow and dust-holding characteristics, so it is important to match the media to the application rather than choosing by size alone.

Some labels also mention whether the media is washable. That can be useful, but washability applies only to specific products. Some filters are designed to be washable - check the product instructions before cleaning or reusing them.

When media matters most

Media type becomes especially important when:

• •The existing system uses a specific resistance range
• •The installation has limited airflow capacity
• •You are moving between coarse, fine or high-efficiency filtration products
• •The site has heavier dust loading than usual

For some buyers, the label may also include a filter class such as G3, G4 or F5 to F9. These are EN 779 classes, which are still widely used in Australia even though EN 779 has been superseded by ISO 16890. If you are comparing products across different standards, do not assume the ratings convert directly.

Frame details that affect fit and handling

The frame is more than just the outer edge. It affects how the filter seals, how it sits in the housing and how it should be installed.

What the frame label may tell you

Look for details such as:

• •Cardboard, metal, plastic or moisture-resistant frame material
• •Single or double-sided seal
• •Gasketed edges
• •Reinforced corners
• •Open-face or header construction on larger filters
• •Directional arrows or airflow marking

These details are especially important in commercial systems where a poor seal can allow bypass around the filter. Even if the size looks correct, the wrong frame style can make installation awkward or ineffective.

Frame shape and depth

Some products share the same face dimensions but differ in depth, pleat spacing or rigidness. That can affect:

• •How many filters fit into the rack
• •Whether the door closes properly
• •Whether the filter collapses or flexes under load
• •Whether the seal remains consistent after installation

If you are comparing product lines, make sure you are not only matching the front dimensions. Check the full construction details on the label or product sheet.

How to read ratings, airflow notes and special markings

Many labels include performance information, but it helps to know what those numbers and terms actually mean.

Efficiency and standard markings

You may see one of the following on the label:

• •MERV rating
• •ISO 16890 classification
• •EN 779 class
• •HEPA class

These systems do not convert directly, so avoid comparing them as if they were identical. If you need to match a replacement filter, compare the actual label data and the intended application rather than relying on a shortcut conversion.

For HEPA products, the label may show H13 or H14. Under EN 1822, H13 is at least 99.95% efficiency and H14 is at least 99.995% efficiency at the most penetrating particle size. These are very specific ratings and should be checked carefully against the system requirements.

Airflow direction and orientation

Many filters have arrows or airflow notes on the frame. These matter because the filter is designed to work in a particular direction.

Always check for:

• •Airflow arrows
• •Upstream and downstream markings
• •Face direction for bag or pocket filters
• •Installation notes for pleated or rigid filters

If the label is missing or unclear, do not assume the orientation. It is better to confirm before fitting the filter.

Practical checklist for buyers comparing labels

When you have two similar products in front of you, use the label to work through the differences before you order.

• •Confirm the exact size, not just the nominal size
• •Match the media type to the existing application
• •Check the frame material, seal and depth
• •Look for airflow arrows or installation notes
• •Compare rating systems carefully and avoid direct conversions
• •Check whether the product is designed for washing before attempting to clean it
• •Keep the original equipment instructions in mind, along with any site-specific requirements

For facility managers and contractors, it can also help to keep a photo of the installed filter label on file. That makes reordering easier and reduces the chance of mixing up similar product lines.

If you manage multiple sites, our products and filter servicing information can also help you identify whether a standard replacement or a more specific custom option is needed.

When a standard filter label is not enough

Sometimes the label does not answer every question. That is common with older systems, custom housings or filters that have been relabelled by different suppliers over time.

A custom-made filter may be the best option when:

• •The size is non-standard
• •The frame depth does not match current product lines
• •The equipment requires a particular seal or construction
• •The site uses a specialised industrial or commercial housing

If you need a replacement for a non-standard size or want to compare options for a specific system, custom air filters can be a practical path forward. For larger sites, commercial filter servicing may also be worth considering.

Need help matching a label to the right filter?

Total Air Filtration is a family-owned air filter manufacturer and supplier based in Hillcrest, Brisbane QLD. If you are unsure how to interpret a label, we can help identify the size, media and frame details and guide you toward the right replacement.

Call 07 3800 3448 or request a quote when you are ready to order. You can also contact us if you want help checking a label before purchasing.