About ACFilterSize

ACFilterSize is a small, independent reference site about HVAC and furnace air filter sizes. Each page answers one measuring question, such as what a 16x25x1 filter really measures or what a MERV number means, using figures published by makers, retailers and public agencies, restated in our own tables with the math shown.

How we source figures

Every figure that comes from a public page links to that page, with the date we last checked it, in a small note right beside the number. The sources are pages anyone can open without signing in.
When a page we cite is repeating someone else's chart (for example a shop publishing a brand's size chart), the note is marked 2nd-hand, and we prefer the original wherever it is public.
If we can't find a reliable public source for something, the page says: "Unverified. We couldn't confirm a reliable source for this yet."
Conversions, areas and fit math are our own arithmetic from the cited figures, and each page says so.

What we are not

We don't sell anything, we aren't affiliated with the brands we mention, and brand names and trademarks belong to their owners. Charts are summarized and restated, never copied. Sizes and specs change, so always check the maker's current documents for the exact model before you buy, cut or install.

How the site is paid for

Some pages may carry affiliate links in the future. See our affiliate disclosure for how that works and how it doesn't affect the numbers.