Duct Gauge Calculator SMACNA

A 60 x 24 supply duct at 2 in. wg? The card reads 22 gauge, T-25a (TDC/TDF) joint, Pittsburgh seam, 1.5 x 1.5 x 1/8 angle reinforcement at 60 in, tie rod flagged, Class A seal, and the allowable leakage CFM for the blower test.
Key the pressure class and the longest side, and the SMACNA-method duct gauge answer is on screen before the drawings are rolled back up.

WHAT GAUGE FOR NEW DUCTWORK
That is the question at the layout table, and the construction schedule card answers it: minimum gauge off the longest side, joint and seam pick, reinforcement member and spacing, tie-rod flag, and seal actions per pressure class. Negative pressure bumps the class before the lookup, the way the tables intend. Every card shows its assumptions (table basis, seam type, pressure class, seal and leakage class) beside the number, so a foreman can check the call before a helper cuts metal.

CHART AND RUN CARDS THAT LEAVE THE PHONE
Saved runs export as printable PDF build cards and CSV schedules, so the gauge chart for the job rides along with the submittal paperwork instead of a photocopied manual page taped to the brake.

GAUGE SELECTION AS PER SMACNA, IN METRIC TOO
Working in mm? The card's gauge picks map to galvanized sheet thickness: 26 ga is about 0.55 mm, 24 ga 0.70 mm, 22 ga 0.85 mm, 20 ga 1.00 mm, 18 ga 1.31 mm. Duct entries are in inches; the thickness conversions above cover metric spec sheets and mm-based submittals.

LEAKAGE TEST, SIZING, AND LAYOUT ON THE SAME JOB
The leakage screen turns the same run into an allowable CFM number and a live PASS or FAIL readout while the blower or hood runs, with a witness field for the test record. Also on board: duct sizing with roughness, friction rate, and velocity shown; offset true length; a square-to-round ordinate table; and a TAB balance ledger.

Core math runs offline with no login, no account, and no cloud sync; paid unlocks for export and saved-card capacity use Google Play Billing.

Field tool only. Gauge selection is a code-compliance floor: verify every output with a competent person against the project spec, the governing standard and edition, and the AHJ. The third-party leakage test is the gate.

SMACNA is a registered trademark of the Sheet Metal and Air Conditioning Contractors' National Association. This app is independent and is not endorsed by or affiliated with SMACNA.