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The main block's long side at the eaves, overhangs included.
Measure the main roof as a rectangle at its drip edge; the wings are added to its long side below.
Tools needed: Tape measure, Plans
The main block's short side at the eaves, overhangs included.
Half of it is each slope's run in plan, which sets the hip lengths and the main ridge on a hipped roof.
One pitch for every plane of the roof.
Rise per 12 of run, not an angle: 6 in 12 is about 26.6°. The slope factor and the hip multiplier both follow from it.
Whether the main roof stops at gable walls or slopes down to eaves at its ends.
Hipped ends turn the gables' rakes into hips and shorten the ridge by the span.
The wing's width at the eaves; no wider than the main span.
The wing comes off the main roof's long side at right angles. Its ridge sits half its span up the slope, so a wing no wider than the main roof ties in below the main ridge with a valley each side.
How far the wing's eaves stand out past the main roof's eaves.
Measured at the eaves, from the main roof's drip edge to the wing's end.
A second wing on the same long side for a U, or opposite it for a T or a cross; 0 for none.
Measured like the first. The two must not overlap along the main roof.
How far the second wing stands out past the main eaves; 0 for none.
Measured at the eaves like the first wing's.
Whether the wings end in a gable or a hip.
A hipped wing end adds two hips and takes half the wing's span off its ridge.
Roof area on the slope
1,417 sq ft
A main roof with gable ends and one wing with gable ends, every plane at a rise of 6 to a run of 12.
- Plan area at the eaves
- 1,267.5 sq ft
- Slope factor
- 1.12
- Ridges
- 61.75 ft
- Hips
- 0 hips
- Hips, lineal
- 0 ft
- Valleys
- 2 valleys
- Valleys, lineal
- 29.25 ft
- Ridges and hips together (ridge cover)
- 61.75 ft
- Eaves
- 84.5 ft
- Rakes (gable edges)
- 79.94 ft
They open the calculator with your figures already in it
L-Shaped and T-Shaped Roof Calculator (Area, Ridges, Hips, Valleys, Eaves and Rakes): 1,417 sq ft — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- Open Exam Prep, Louisiana roofing contractor guide, 3.2 Surface Area Calculations, Roofing Squares, Pitch Multipliers and Slope Formulas: actual sloped surface area = horizontal footprint area x the pitch multiplier sqrt(12² + R²) / 12; a standard hip roof has the same surface area as a gable roof over the same footprint, overhangs and slope; the hip and valley multiplier sqrt(12² + 12² + R²) / 12 from the 17-inch diagonal run (1.500 at 6:12); length of one hip rafter = common run x the hip multiplier
Inputs used
- Main Roof Length (along its ridge)
- 39 ft
- Main Roof Span (eave to eave)
- 26 ft
- Roof Pitch (rise per 12 run)
- 6
- Main Roof Ends
- Gable ends
- First Wing Span (0 for none)
- 19.5 ft
- First Wing Projection
- 13 ft
- Second Wing Span (0 for none)
- 0 ft
- Second Wing Projection
- 0 ft
- Wing Ends
- Gable ends
Intermediate steps
- Plan area at the eaves
- 1,267.5 sq ft
- Slope factor
- 1.12
- Ridges
- 61.75 ft
- Hips
- 0 hips
- Hips, lineal
- 0 ft
- Valleys
- 2 valleys
- Valleys, lineal
- 29.25 ft
- Ridges and hips together (ridge cover)
- 61.75 ft
- Eaves
- 84.5 ft
- Rakes (gable edges)
- 79.94 ft
Confidence note: A main roof with gable ends and one wing with gable ends, every plane at a rise of 6 to a run of 12.
What this calculation does not cover
- One pitch everywhere. A wing at another pitch, a lean-to or a flat section changes every hip and valley; work such a roof plane by plane.
- The outline is a main rectangle and up to two wings off one long side, measured at the eaves with the overhangs in. A wing off an end, a wing wider than the main span, a courtyard or a wing that meets another wing are not modelled.
- Lengths are the lines of the roof's edges and intersections, not cut lengths of timber or flashing: laps, waste, and the extra at a hip's or valley's ends are the covering's and the trade's.
- Dormers, chimneys and rooflights are not taken off or added; the slope area is the whole roof plane.
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.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-10-10 · v1.0.0
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