Free Furnace & AC Filter Sizing Tool

HVAC Filter Size Calculator

Estimate the filter face area needed for a known HVAC airflow, find a nearby common nominal filter size, or calculate approximate face velocity through your existing furnace or AC filter.

Calculate HVAC Filter Size

HVAC Filter Area & Airflow

Size the filter from airflow, not guesswork.

If you do not know system airflow, estimate it first with the HVAC CFM calculator . If you already know the filter size and only need a replacement schedule, use the HVAC filter change calculator .

Calculate HVAC Filter Face Area

Estimate required filter area or check airflow through an existing nominal filter size.

Calculation Method

HVAC Airflow (CFM) Enter estimated system airflow through the filter bank.

Planning Filter Face Velocity This is a planning input, not a manufacturer pressure-drop specification.

Number of Filters Sharing Airflow

Filter Depth / Thickness Depth is displayed for reference. It does not change the face-area calculation.

Existing Filter Nominal Width (in)

Existing Filter Nominal Height (in)

Number of Identical Filters

Common Nominal Filter Size Reference - -

Filter dimensions alone do not determine pressure drop. Filter construction, media area, pleat depth, MERV rating, loading condition and manufacturer performance data also affect resistance to airflow.

- Face Velocity

HVAC Airflow -

Total Face Area -

Number of Filters -

Area Per Filter -

How the filter-size estimate works

Required filter face area is estimated from airflow ÷ target face velocity. The calculator then searches a list of common nominal residential filter dimensions for an area that meets or exceeds the calculated per-filter area.

Nominal vs actual dimensions: a filter labeled 20 × 25 × 1 inches may have slightly smaller actual dimensions. Always check the existing filter label, cabinet or return grille opening before purchasing a replacement.

Filter restriction or airflow problem?

Request HVAC help below if you want to provide your Texas location and information about the HVAC system, filter setup and airflow concern.