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Roof Overhang Tail Length Calculator

Convert a desired horizontal roof overhang into the actual rafter tail length measured along the roof slope.

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

Rafter tail length

2.2 ft

High confidence

At the values currently entered, the rafter tail length works out to 0.67 m. Figures are shown for United States, where IRC 2024 is the governing residential reference; switch the market above if you are building elsewhere.

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

  • The rafter tail's along-slope length equals the horizontal overhang × √(1+(pitch/12)²), the same slope factor used for common rafter length

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Frequently asked questions

Why is the rafter tail longer than the horizontal overhang?
The rafter tail runs along the sloped roof plane, not horizontally — the steeper the pitch, the more the along-slope distance exceeds the flat horizontal overhang distance you actually want at the eave.
Is this the same slope factor used for common rafter length?
Yes — the √(1+(pitch/12)²) factor converts any horizontal run on the roof plane into its along-slope length, whether that run is the main rafter span or just the overhang beyond the wall.
Does this include the fascia board or trim thickness?
No — this is the rafter tail's structural length along the roof slope only. Fascia, soffit, and trim details are not included and should be accounted for separately when cutting rafter tails.