What size is a 18 x 20 x 1 air filter?

A 18 x 20 x 1 filter has a nominal (printed) size of 18 x 20 x 1 inches, written as length by width by depth. Its actual measured size is about half an inch smaller on the length and width so it seats properly. Always order by the nominal size.

Is a 18x20 the same as a 20x18 filter?

Yes. The length and width are interchangeable, so a 18x20x1 and a 20x18x1 are the same filter. Only the depth has to match exactly.

How often should I change a 18 x 20 x 1 filter?

A 1-inch filter is typically changed every 1 to 3 months; thicker 2-inch and 4-inch filters can last 3 to 6 months or more. Homes with pets, allergies, or heavy use should change more often.

18x20x1 1in HVAC Air Filter

$12.99

MERV Rating

Clear

Need a different filter size? Not the size you’re looking for? Use our finder to get to the exact size you need in seconds.

Find your size

Air Filter Sizing & Replacement Guide

This is a standard pleated HVAC and furnace filter. The size printed on the frame is the nominal size — the number you order by. The filter itself measures slightly smaller so it seats and seals correctly.

Nominal size

—

Actual size (approx.)

—

Depth

—

Orientation

Interchangeable

⚠ Nominal vs. actual size. If you measure this filter with a tape it reads about ½ inch smaller per side. That gap is intentional — it lets the filter slide in and seal. Always order by the nominal (printed) size.

Which MERV rating should you choose?

MERV (Minimum Efficiency Reporting Value) measures how much a filter captures. Higher isn’t always better — it has to match what your system’s airflow can handle. Here’s the plain-English version.

MERV 8

Everyday protection

Captures dust, lint, pollen, and mold spores. The right choice for most homes and rentals.

MERV 10

A step up

Adds finer dust, pet dander, and smog particles. A modest upgrade for allergy-aware homes.

MERV 13

Best air quality

Captures very fine particles — smoke, bacteria, and virus carriers. Best where indoor air quality matters most.

How often should you change this filter?

A clogged filter makes your system work harder, raises energy bills, and lets dust through. Here’s a realistic schedule for a 1-inch filter — adjust based on your home.

Every 1–2 monthsHomes with pets, smokers, or allergies

Every 2–3 monthsTypical household — the sweet spot

Every 3 months maxVacant or low-use spaces

Not sure you’ll remember? That’s exactly what our auto-delivery is for — the right filter shows up on your schedule, so a missed change never becomes a frozen coil or a tenant complaint.

Managing filters across multiple units?

We map every size across your property, auto-ship before you run out, and document every change for compliance.

Get a free site audit →

Common questions

What size is this air filter?

Filter sizes are written as length × width × depth in inches. The number on the frame is the nominal (rounded) size — that’s what you order by. The actual filter measures about half an inch smaller on length and width (and a 1-inch filter is about ¼ inch less deep) so it seats properly.

Does the order of the numbers matter?

No. Length and width are interchangeable — a 16×25 and a 25×16 are the same filter. Only the depth (the third number) has to match your system exactly.

What does MERV mean?

MERV (Minimum Efficiency Reporting Value) rates how effectively a filter captures particles, on a scale from 1 to 16 for residential filters. MERV 8 handles everyday dust and pollen; MERV 13 captures very fine particles. Match it to your needs and your system’s airflow.

How does Subscribe & Save work?

Choose Subscribe & Save above and tell us how often you want deliveries. The right filter ships automatically at 15% below the one-time price. Skip, reschedule, or cancel anytime — no contracts.