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Blower Door CFM50 Target Calculator

Find the target CFM50 blower door reading needed to hit a specific ACH50 airtightness goal.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-25 · v1.0.0

Market
Imperial · sales tax
7.87 ft
Schematic, drawn to the proportions you entered — not to scale on screen.

Target CFM50

423.78 CFM50 (target maximum)

High confidence

Your actual blower door test result should come in at or below this target — this is the inverse of the Air Changes Per Hour Calculator, useful for setting a goal before construction or air sealing work rather than evaluating a completed test.

Building volume
8475.52 ft³

For the dimensions entered, expect a target cfm50 of 424 CFM50 (target maximum). Set for United States against IRC 2024. The market selector changes both the units and the code cited.

Add the equipment this sizes

This result is a specification — 423.776 CFM50 (target maximum) — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • Standard blower door formula rearranged: target CFM50 = (target ACH50 x building volume in cubic feet) / 60

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Frequently asked questions

When would I use this instead of the Air Changes Per Hour Calculator?
Use this one before construction or an air-sealing project, to know what CFM50 result you're aiming for. Use the Air Changes Per Hour Calculator afterward, once you have an actual blower door test result, to see what ACH50 you achieved.
Is hitting the target guaranteed by good workmanship alone?
Careful air sealing (caulk, foam, taped sheathing seams, sealed penetrations) is the main driver, but the actual result depends on many construction details — most builders targeting an aggressive ACH50 use a blower door test mid-construction to catch and fix leaks before drywall closes up the walls.
Does a lower target always cost more to achieve?
Generally yes, especially at the tightest levels (well under 1 ACH50) which require deliberate air-sealing details throughout construction — but many of the basic measures that get a home to a moderate target (3-5 ACH50) are low-cost, common-sense sealing practices.