Chapter 01Records · Tool and printable record
HVAC filter size finder and replacement planner
The size printed on a filter is its nominal size, rounded up. Filterbuy's size chart lists the actual length and width as half an inch smaller and a 1-inch filter as 0.75 inch deep, so a 16x25x1 filter measures about 15.5 x 24.5 x 0.75 inches. The EPA says manufacturers typically recommend a new filter every 60 to 90 days, and ENERGY STAR's checklist says to inspect, clean or change it once a month.
Source: Filterbuy air filter size chart, checked October 9, 2026; EPA, Guide to Air Cleaners in the Home, checked October 9, 2026; ENERGY STAR maintenance checklist, checked October 15, 2026.
HVAC filter size finder and replacement planner
Actual size, about 19.5 x 24.5 x 0.75 in (495 x 622 x 19 mm)
- Next change window
- December 4, 2026 to January 3, 2027
- Filters a year, per slot
- 4 to 6
- Monthly checks
- November 5, 2026; December 5, 2026; January 5, 2027
How to use this, in plain words
Slide the old filter out and look at the cardboard edge of the frame. The size is printed there, usually as three numbers such as 16x25x1.
No print on the frame? Measure the old filter's length, width and depth in inches, to the nearest quarter inch, and choose the measured mode.
Read both sizes: the nominal size to search for in a store, and the actual size the tape measure should show.
Type the date you put the new filter in. The tool gives the 60 to 90 day change window and monthly check dates.
Write the size on the printable sheet and keep it near the return grille, so nobody has to pull the filter out to find it next time.
Source: Filterbuy air filter size chart, checked October 9, 2026; EPA, Guide to Air Cleaners in the Home, checked October 9, 2026; ENERGY STAR maintenance checklist, checked October 15, 2026.
Before you start
- Note 01
Measured mode is for a flat filter
The measured mode expects the old filter's own size. A filter that has bowed reads short; measure the slot instead and round each side, as the no-size guide shows.
- Note 02
Get the depth right
Length and width can be listed in either order on a box. The depth, the smallest number, has to match the slot.
- Note 03
Check every grille
Some homes have more than one return grille, each with its own filter. Look at all of them before you buy a multipack.
- Note 04
Buy for the year
At one filter every 60 to 90 days, a year takes 4 to 6 filters.
Source: Filterbuy, How to Measure Your Air Filter, checked October 9, 2026; EPA, Guide to Air Cleaners in the Home, checked October 9, 2026.
How it works
- Nominal to actual: subtract 0.5 inch from the length and the width. Depth: a 1-inch filter is 0.75 inch, a 2-inch is 1.75 inches and a 4-inch is 3.63 inches.
- Actual to nominal: add 0.5 inch to the measured length and width and round to the nearest whole inch. Match the measured depth to the nearest depth in the chart. If a side lands more than a quarter inch off that pattern, the tool flags it so you look for the printed size.
- Next change window: install date + 60 days to install date + 90 days. Filters a year: 365 ÷ 90 and 365 ÷ 60, rounded, which is 4 to 6.
- Monthly checks: the same day of the month for the next three months.
Source: Filterbuy air filter size chart, checked October 9, 2026; EPA, Guide to Air Cleaners in the Home, checked October 9, 2026; ENERGY STAR maintenance checklist, checked October 15, 2026.
Worked example
The old filter's frame says 20x25x1, and you put a new one in on October 5, 2026.
- Length and width: 20 − 0.5 = 19.5 in, and 25 − 0.5 = 24.5 in. Depth: a 1-inch filter is 0.75 in.
- Actual size: about 19.5 x 24.5 x 0.75 in (495 x 622 x 19 mm).
- Next change: October 5, 2026 + 60 days = December 4, 2026, and + 90 days = January 3, 2027.
- Over a year: 365 ÷ 90 ≈ 4 and 365 ÷ 60 ≈ 6, so 4 to 6 filters for this slot.
If the answer surprises you
The filter measures smaller than its label
That is how filters are sold. Filterbuy's chart lists the actual length and width as 0.5 inch under the nominal size, and a 1-inch filter as 0.75 inch deep.
Source: Filterbuy air filter size chart, checked October 9, 2026.
Your measurement matches no size
Brands trim a little differently, and Filterbuy says its pattern is not a standard. When a side is more than a quarter inch off, the tool flags it; look for a printed size on the old frame or in the equipment manual.
Source: Filterbuy air filter size chart, checked October 9, 2026.
The change window looks short or long
The 60 to 90 day window is the EPA's summary of what manufacturers typically recommend. If your equipment maker gives an interval, use theirs.
Source: EPA, Guide to Air Cleaners in the Home, checked October 9, 2026.
What to record
The filter size is easy to forget between changes. The printable record keeps it, one row per slot, with these columns:
- Slot location (hall return grille, furnace cabinet, air handler)
- Nominal size printed on the frame
- Measured actual size
- Brand and rating printed on the filter
- Date changed
- Next change window
- Price per filter (USD)
Variants
More than one return grille
Give each slot its own row. Two slots in the same house can take different sizes.
If you rent
Find out whether you or the landlord changes the filters, and log the dates either way so you can show when it was done.
Missing label
Use the second mode: measure the old filter's length, width and depth, and the tool gives the nominal size to look for.
Numbers this tool uses
- Actual length and width0.5 in under the nominal size Filterbuy air filter size chart, October 9, 2026
- Actual depth of a 1-inch filter0.75 in Filterbuy air filter size chart, October 9, 2026
- Actual depth of a 2-inch filter1.75 in Filterbuy air filter size chart, October 9, 2026
- Actual depth of a 4-inch filter3.63 in Filterbuy air filter size chart, October 9, 2026
- Typical replacement interval60 to 90 days (manufacturers' typical recommendation) EPA, Guide to Air Cleaners in the Home, October 9, 2026
- Check intervalOnce a month ENERGY STAR maintenance checklist, October 15, 2026
Limitations
- Planning estimate; check the manufacturer's dimensions printed on the filter frame and in your system's manual.
- The half-inch pattern comes from one manufacturer's chart. Filterbuy itself notes it is not a published standard, so other brands can differ slightly.
- When your equipment maker gives a replacement interval, use theirs. This tool measures, records and schedules. It does not cover HVAC repair or choosing a filter rating.
Tips and tricks
- Tip 01
Check the arrow before the grille closes
Most filters print an airflow arrow on the frame. It points away from the room and toward the furnace or air handler.
- Tip 02
Write the size on the duct
A marker note next to the slot saves you from pulling the old filter out in the store aisle next time.
- Tip 03
Photograph the label
A phone photo of the old filter's edge keeps the size, the brand and the rating together. Put it in a home records album.
- Tip 04
Store spares flat
A bent frame or a crushed corner lets air slip around the filter. Keep the multipack flat and dry.
- Tip 05
Date the frame
Write the change date on the new filter with a marker. When you check it next month, you will know how long it has been in.
What we would do
Buy one filter first, then the multipack
Buy a single filter in the size the finder gives and check that it slides in snug with the arrow the right way. Once it fits, buy a year's supply in that exact size and add the change dates to your calendar or the printable planner.
Questions
Why doesn't my 16x25x1 filter measure 16 by 25 inches?
16x25x1 is the nominal size, rounded up. Filterbuy's chart gives its actual size as 15.5 x 24.5 x 0.75 inches, a little smaller so it slides into the slot.
Source: Filterbuy air filter size chart, checked October 9, 2026.
Should I measure the old filter or the slot?
Read the size printed on the old filter's frame first. If it has worn off and the old filter is still flat, measure it and use the actual-to-nominal mode. If it has bowed, measure the slot instead and round each side to the nearest inch, as Filterbuy advises. The EPA says a filter should fit snugly, so air doesn't leak around it, without being bent or crushed to fit.
Source: EPA, Guide to Air Cleaners in the Home, checked October 9, 2026; Filterbuy, How to Measure Your Air Filter, checked October 9, 2026.
How often should I change the filter?
Follow your equipment maker's interval if it gives one. The EPA says manufacturers typically recommend every 60 to 90 days, and ENERGY STAR's checklist says to inspect, clean or change filters once a month.
Source: EPA, Guide to Air Cleaners in the Home, checked October 9, 2026; ENERGY STAR maintenance checklist, checked October 15, 2026.
How many filters should I buy for a year?
At one change every 60 to 90 days, that is 4 to 6 filters a year per slot. Write the size on the record sheet so the next order is quick.
Source: EPA, Guide to Air Cleaners in the Home, checked October 9, 2026.
Part of a system
This page is one part of a bigger job. The system page puts the parts in order.
SystemFall home checklist and winter-prep recordWhat to book, check and write down before winter: the heating check-up, the air filter, smoke alarm tests, hoses and drafts, on one printable page.8 steps · 4 parts · 1 page to printOpen the system
SystemFurnace filter record: every slot, its size and the change datesFind every filter slot, write down its size and arrow, buy a year of spares, then check monthly and log each change on one printable record.8 steps · 4 parts · 1 page to printOpen the system
SystemHome records binder: your house manualSix tabs for the facts a house keeps asking for: appliances and warranties, filter sizes, paint colors, measurements, manuals and service visits.8 steps · 6 parts · 1 page to printOpen the system
SystemMonthly house checkOne page for the monthly house check: test each smoke and CO alarm, look at the filter, read the water meter, check under the sinks, write one line.8 steps · 7 parts · 1 page to printOpen the system
SystemMove-in first month: the new home checklistFour weeks, one short job list each: smoke alarms, the air filter, appliance labels, a room-by-room inventory and the monthly reminders, on one printable page.9 steps · 6 parts · 1 page to printOpen the system
SystemSpring home checklist and leak-check recordThe spring list for a US home on one printable page: book the cooling check-up, date and test every alarm, check the filter, run the two-hour leak check.9 steps · 6 parts · 1 page to printOpen the system- SystemSummer cooling-season recordOne printable page for the cooling season: the AC model and age, the spring check-up, a filter date each month, hot rooms and bills to show the contractor.8 steps · 7 parts · 1 page to printOpen the system
Guides that go deeper
ProblemNo size printed on my air filter: how to find itThe print on the frame is gone or the slot is empty. Measure the opening, round to the nearest inch, and know when you need a custom size.Read the guide
Practical noteFilter change reminders that actually stickA monthly look on a fixed day, the date written on the frame, a 60 to 90 day change window, and the next filter already on the shelf. Set up in ten minutes.Read the guide
Practical noteTwo return grilles, two sizes: keeping a filter logFind every filter slot, number them, and give each its own line: size, date in, next change. A worked log for a 20x25x1 and a 14x20x1 in one house.Read the guide
Related tools
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Chapter 05Home maintenance calendarPick your climate region, say whether you own or rent and tick what the house has. Get a year of household jobs by month and a year sheet to print.Open the tool- Chapter 01All records toolsPrintable home records with a calculator behind each one: appliance and warranty log, HVAC filter sizes and change dates.Open the chapter
Sources
- Air Filter Sizes: Nominal vs. Actual Dimensions, Filterbuy (US air filter manufacturer). Checked October 9, 2026.
- Guide to Air Cleaners in the Home, U.S. Environmental Protection Agency. Checked October 9, 2026.
- Heating and Cooling Maintenance Checklist, ENERGY STAR (U.S. EPA and DOE). Checked October 15, 2026.
- How to Measure Your Air Filter: Complete Step-by-Step Guide, Filterbuy (US air filter manufacturer). Checked October 9, 2026.
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