Build · Framing
Estimate common-rafter line length from rise/run or pitch + span. Geometry only — not span tables.
Geometry only — not an IRC span-table design.
Scenario templates
Total rafter length (with overhang)
14.534
Line length 13.416 + overhang along slope 1.118
Common-rafter diagram
Line length = √(rise² + run²). Overhang is entered horizontal and converted along the slope. Not a birdsmouth layout.
Need X/12 · degrees · % together? Open the roof pitch calculator.
Estimate only — not a substitute for IRC R802.4 span tables, engineered plans, birdsmouth layout, or a local code check. Member size and allowable span must come from the adopted code tables or a licensed design professional. We do not copy copyrighted span tables here.
Line length √(rise²+run²), plumb-cut angle, overhang converted along the slope, and total planning length. Span mode splits (span − ridge) ÷ 2 for each side’s run.
Does not replace
Supply yard
Starting points for planning — not a site-specific design. Footnotes point to sources on this page.
| Topic | Typical starting value | Source notes |
|---|---|---|
| How code sizes rafters | Use IRC R802.4 span tables (adopted edition) or AWC tables | IRC R802.4.1 concept via Building Code Trainer / UpCodes mirrors — we do not reproduce copyrighted tables. |
| Span measurement | Horizontal projection of the rafter | IRC R802.4.1 language as commonly summarized in code commentaries. |
| When tables are not enough | Loads/species/tie location outside table scope → engineering practice | Building Code Trainer overview of R802.4 limits (raised ties, load beyond tables, etc.). |
| This calculator’s role | Length & angle planning only | YardBuild Tools disclaimer — pair with span tables or a licensed designer for member size. |
Short DIY narratives. Numbers match the one-click scenario presets in the calculator (US units).
Use this when you need a cutting-length ballpark from pitch and span — the same geometry DIY framers sketch before a lumber run. Pair the length with IRC span tables or engineered plans for depth, grade, and spacing.
The International Residential Code provides prescriptive rafter span tables (R802.4.1 series in recent editions). Those tables are copyrighted; allowable spans depend on species, grade, spacing, and loads. We link to explanations of the concept and tell you to use the adopted code book, AWC resources, or a licensed design professional — we will not paste fake span numbers.
Line length = √(rise² + run²). Angle θ = arctan(rise ÷ run). In pitch + span mode, run = (span − ridge thickness) ÷ 2 and rise = (pitch12 ÷ 12) × run. Overhang along slope = overhanghorizontal ÷ cos(θ).
No. This tool estimates common-rafter line length and plumb-cut angle from rise/run or pitch + span. Member size still comes from IRC R802.4 span tables (adopted edition), AWC resources, or a licensed designer — we do not reprint copyrighted tables.
Line length = √(rise² + run²). In pitch + span mode, run = (span − ridge thickness) ÷ 2 and rise = (pitch₁₂ ÷ 12) × run. Overhang along the slope = overhang_horizontal ÷ cos(θ).
No — this is common-rafter geometry only. Hip/valley and birdsmouth layout need additional framing methods or engineered plans.
We cite extension services, manufacturer guidance, and municipal/IRC reprints. This is not legal advice, not a substitute for a licensed engineer or architect, and not approval from your Authority Having Jurisdiction (AHJ). Adopted codes and product warranties vary by place and year — verify before you buy or cut.
States absolute minimum asphalt-shingle slope 2:12; 2:12 to <4:12 treated as low slope needing double underlayment; typical residential often 4:12–9:12.
Explains IRC R802.4 span-table concept, loads, and when engineering practice is required. We do not reproduce copyrighted span tables.
Shows that rafters are sized from IRC Tables R802.4.1(1)–(8); spans measured on horizontal projection. Confirm adopted edition with your AHJ.
Full site bibliography: Sources hub.
Yards, tons, density table, overage vs compaction, optional cost.
Buy-depth after existing, bags↔bulk ledger, multi-bed, coverage table.
X/12, degrees, % slope, rafter teaser, pitch compare.
Deck rise, treads, Standard/Flush mount, 3D stairs.
Stringer length + IRC R311.7 table on one screen.
