Basic pleated 20×25×1
Standard dust and pollen capture. Good for rental units and systems that need easy airflow. Look for multipacks so you change on schedule.
20×25×1 Furnace Filter: Nominal vs Actual Size + Best MERV Picks
One of the most common residential 1-inch furnace / AC filter sizes. Buy the printed size 20×25×1. Your tape will read smaller — that is expected.
Quick answer
Order the printed size 20x25x1 (also written 20×25×1).
A tape measure on the frame usually reads about 19½–19¾″ × 24½–24¾″ × ~¾″, not a full 20 × 25 × 1. That undercut is how the panel slides into the rack. Brands do not cut the same nominal identically — see the chart below.
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Nominal vs actual size
Nominal is the whole-inch label on the cardboard frame and in the product title — what you order. Actual is the cut that has to fit the slot. There is no single industry-wide actual for every brand.
| Brand / listing | Published actual (in.) | Source |
|---|---|---|
| Honeywell 1″ Standard / High / Ultra Efficiency (MERV 8, 11, 13) | 19.75 × 24.75 × 0.75 | Honeywell Store product specs (via merchant listings) |
| Amazon Basics 20×25×1 MERV 8 (example SKU) | 19.75 × 24.75 × 0.75 | Amazon product title / dimensions (e.g. B088BZ3BDX) |
| Filtrete 20×25×1 MPR 2200 / MERV 13 | 19.69 × 24.69 × 0.78 | Filtrete listing “exact dimensions” |
| Filtrete 20×25×1 MPR 1000 / MERV 11 (typical listing) | ~19.68 × 24.68 × 0.81 | Filtrete Amazon titles listing “Actual Size” |
| Nordic Pure 20×25×1 pleated (typical) | ~19.5 × 24.5 × 0.75 (19½ × 24½ × ¾) | Nordic Pure merchant listings |
How to measure the old cartridge
- Pull the filter. Read the printed nominal size on the frame first.
- Measure outside of frame to outside of frame (width, then height, then thickness). Do not measure across the soft pleats only.
- Compare your measured numbers to the brand’s published actual — not to 20.00 × 25.00 × 1.00.
- If you switch brands (e.g. Nordic Pure ~19.5 × 24.5 → Honeywell 19.75 × 24.75), expect a snugger slide-in.
Some Filtrete SKUs print slightly different “actual” figures on different pack sizes. If the rack is tight, measure what is in it before you change brands.
MERV 8 vs 11 vs 13 for this slot
For a 20×25×1 rack, efficiency and airflow trade off more than on a deep 4–5″ media cabinet. Guidance below follows EPA’s MERV overview and common residential practice — check your furnace manual if unsure.
| MERV | What it is for | Airflow note |
|---|---|---|
| 8 | Everyday dust, lint, pollen. Fine default for many homes. | Least restrictive in a thin 1″ slot. |
| 11 | Pets, mild–moderate allergies, finer household dust. | Moderate step-up; usually OK on modern systems. |
| 13 | Finer particles and smoke; EPA notes MERV 13+ when upgrading if the system can handle it. | Highest resistance of these three in a 1″ frame. Confirm the blower can push air through it. |
When not to jump to MERV 13 in a 1″ slot
- Older PSC-blower furnaces that already struggle with airflow
- Weak supply registers, frequent high-limit trips, or AC coil freeze-ups after a prior filter upgrade
- You cannot change the filter often (a clogged high-MERV filter restricts more than a clean mid-MERV one)
Safer paths for fine filtration: a deeper media cabinet (4–5″) with MERV 13, or stay at MERV 11 in the 1″ rack until a technician checks static pressure. Source: EPA — What is a MERV rating?
Best buys for 20×25×1
We describe product types by MERV tier — not specific dollar prices, star ratings, or unverified specs. After affiliate enrollment, deep links will point at current in-stock SKUs.
Allergy / pet step-up
Common residential upgrade for dander and finer dust without jumping straight to MERV 13 in a thin rack.
Fine-particle / smoke tier
Use only if your system can handle the pressure drop (see MERV section). Brands such as Filtrete publish exact actual sizes on the listing — match them if the slot is tight.
Stock up or schedule delivery
A 1″ filter is often changed every 1–3 months (sooner with pets or wildfire smoke). Multipacks and subscription delivery reduce “forgot to buy” gaps.
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Will a different size work?
- Never larger than the rack (e.g. do not force a 20×25 into a 16×25 slot).
- Never the wrong depth — a 4″ media filter will not fit a 1″ rack, and a 1″ filter in a 4″ cabinet leaves bypass gaps unless the cabinet is designed for it.
- Emergency smaller only: a slightly smaller panel can let unfiltered air bypass around the edges. Only as a short-term stopgap until the correct 20×25×1 arrives; tape is not a fix for wrong size.
- Brand-to-brand actual differences of ~0.1–0.25″ on a face are normal; switching from a small cut to a large cut can feel tight without being “wrong size.”
How often to replace a 20×25×1
- Typical 1″ pleated: about every 30–90 days. Follow the filter maker’s label; dirty homes need the short end of that range.
- Pets / shedding: check monthly; many households change every 30–45 days.
- Wildfire smoke / renovation dust: inspect every 2–4 weeks; replace when the media looks gray or airflow drops.
- Thicker media (4–5″): often lasts 6–12 months — different product, different slot. Do not apply that interval to a 1″ filter.
A clogged filter raises static pressure regardless of MERV. When in doubt, hold the used filter up to a light — if little light passes, replace it.
FAQ
Does my furnace model set the filter size?
No. The filter slot / cabinet / return grille sets the size. Two homes with the same furnace brand can take different filters. Always use the printed size on the filter that came out of your slot.
I have two filters — do both need to be 20×25×1?
Not necessarily. Some systems have a filter at the furnace and another at a return grille, and they can be different sizes. Measure / read each one separately.
My tape says 19.7 × 24.7 — what do I buy?
Buy 20×25×1 if that is what the old frame was labeled, or if your measurements match the published actuals in the chart above. Ordering “19.7×24.7” as a custom size is rarely needed for standard residential racks.
Which way does the arrow go?
Airflow arrow points toward the furnace / blower (the direction air travels). Match the old filter’s orientation if you photographed it before removal.
Is 20×25×1 the same as 20×25×4?
No. Same face size family, different thickness and usually a different cabinet. A 4″ filter needs a media filter cabinet; do not fold or stack 1″ filters to fake depth.
Next sizes
Coming next on the shipping queue (links go live as each page ships):
Get this size on a delivery schedule
If you want automatic replacements on a 1–3 month cadence, filter-delivery services stock 20×25×1 across MERV tiers.
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