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Rectangular Sheet Metal Duct Surface Area Calculator

Calculate the sheet metal surface area needed to fabricate a straight run of rectangular duct, with a waste allowance.

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 2026-08-26 · v1.0.0

Market
Imperial · sales tax
32.81 ft1.31 ft
Schematic, drawn to the proportions you entered — not to scale on screen.
Who is doing the work?

The standard allowance most suppliers and estimating guides assume for ordinary work.

Sheet metal surface area needed

165.76 ft²

High confidence
Base surface area (before waste)
150.69 ft²

With the figures above, the sheet metal surface area needed comes to 15.4 m². Behind that figure, base surface area (before waste) is the biggest single quantity at 14 m²; start there if the total looks wrong. This is calculated for United States and cites IRC 2024. Building in another market? Change the selector above so the units and code reference follow.

Estimated cost — your price

This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.

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

  • Surface area = 2 × (Width + Height) × Length (perimeter × length), the standard method for straight rectangular duct fabrication material takeoff — fittings/transitions are taken off separately by piece. A waste/scrap allowance (commonly ~10% for shop-fabricated duct, more for field fabrication) is a standard estimating convention, not a code requirement.

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Frequently asked questions

How is the sheet metal surface area calculated?
It's the duct's perimeter — 2 × (Width + Height) — multiplied by the straight run length, the standard method for rectangular duct fabrication material takeoff.
Does this include fittings, elbows, or transitions?
No — this covers straight duct runs only. Fittings, transitions, and elbows are taken off separately by piece since their surface area doesn't scale linearly with a simple perimeter × length formula.
Why add a waste/scrap allowance?
Sheet metal fabrication always loses some material to seams, laps, and cutting waste. A waste allowance of around 10% is a common estimating convention for shop-fabricated duct — it isn't a code requirement, and field fabrication with less efficient cutting may warrant a higher allowance.