The job
Modelled, not recorded. Every figure here is the answer the L-Shaped and T-Shaped Roof Calculator (Area, Ridges, Hips, Valleys, Eaves and Rakes) gives for these inputs, written down in both unit systems and re-run whenever the site is built. No job was carried out, so there is no measured overrun on this page.
The house is a single-storey ranch on an L-shaped plan. The main block is 44 ft (13.41 m) long and 28 ft (8.53 m) from eave to eave, with hipped ends; a wing 22 ft (6.71 m) wide projects 16 ft (4.88 m) from it, under its own gable roof whose ridge runs into the main roof's slope. Where the two roofs meet they form a pair of valleys.
Every dimension is taken at the eaves, overhangs included, because the roof covering runs to the drip edge and not to the walls. On an existing house that means measuring the overhangs from the ground or from the roof, as the guide linked below describes, and adding them to the wall dimensions.
Both roofs are at a 6/12 pitch, the same on every slope, which is what the calculator assumes. A house whose wing is steeper or shallower than the main roof is measured as two separate roofs and the results added.
The inputs, exactly as entered
| Input | Value | Why |
|---|---|---|
| Main Roof Length (along its ridge) | 44 ft (13.41 m) | Along the main roof's ridge direction, eave to eave at the hipped ends, overhangs included. |
| Main Roof Span (eave to eave) | 28 ft (8.53 m) | Across the main roof from eave to eave, overhangs included. |
| Roof Pitch (rise per 12 run) | 6 | Left at the calculator's own default. |
| Main Roof Ends | Hipped ends | The main roof is hipped at both ends, which turns its gable edges into four hips. |
| First Wing Span (0 for none) | 22 ft (6.71 m) | The wing's span from eave to eave, across its own ridge. |
| First Wing Projection | 16 ft (4.88 m) | How far the wing's roof runs out from the main roof's eave line. |
| Second Wing Span (0 for none) | 0 ft (0 m) | Left at the calculator's own default. |
| Second Wing Projection | 0 ft (0 m) | Left at the calculator's own default. |
| Wing Ends | Gable ends | Left at the calculator's own default. |
The working, step by step
1. Plan area at the eaves
1,584 sq ft (147.2 m²)
The main rectangle plus the wing's projection gives the plan, 1,584 sq ft: the shadow the roof would cast at noon. It is the starting point for everything, and the reason the dimensions must include the overhangs.
2. Slope factor
1.12
At this pitch the roof surface is longer than its plan by a factor of 1.12, the hypotenuse of twelve units of run and the rise, as the calculator's source states. The plan times this factor is the area on the slope in the headline.
3. Ridges
43 ft (13.11 m)
The ridges are the level lines at the top: the main ridge, shortened by the hips at each end, and the wing's ridge running into the main slope, 43 ft in all. They are capped, so their length is a purchase.
4. Hips, lineal
84 ft (25.6 m)
The hipped ends add 4 hips rising from the corners to the ridge, 84 ft together. A hip is longer than the slope beside it because it runs diagonally across the plan as well as up it, which the calculator's hip multiplier accounts for.
5. Valleys, lineal
33 ft (10.06 m)
Where the wing meets the main roof, 2 valleys run down to the eave, 33 ft together. Valleys collect the water of two slopes, so they are lined with valley material and a membrane for their full length.
6. Eaves
154 ft (46.94 m)
The eaves, the level lower edges round the whole roof, total 154 ft. Drip edge, starter course and gutters are all bought by this length, which on a hipped roof runs all the way round.
7. Rakes (gable edges)
24.6 ft (7.5 m)
Only the wing's gable has sloping edges, 24.6 ft of rake. A rake is finished with drip edge and a starter or trim of its own, and on this roof it is a short length because the main block has none.
Roof area on the slope
1,771 sq ft
164.5 m²
The roof is 1,771 sq ft on the slope, which is 164.5 m²; divided by a hundred square feet that is the number of roofing squares the shingle calculator starts from. The edges are the rest of the order: 127 ft of ridge and hip to cap, 33 ft of valley to line, 154 ft of eave and 24.6 ft of rake for the drip edge. A roof with dormers, chimneys or skylights needs them measured and added by hand.
What to buy
| Quantity | Figure | What it is for |
|---|---|---|
| Roof area on the slope | 1,771 sq ft (164.5 m²) | Not bought as such: the area on the slope that the shingles, underlayment and deck are ordered from. |
The allowance, and what it does here
This calculator measures and does not add an allowance, because the right allowance depends on the covering. What the measurement tells you is where the waste will be: every hip and valley is a line where shingles are cut at an angle, so a roof with long hips and valleys wants a larger allowance than a plain gable of the same area. Use these lengths to choose it in the shingle calculator rather than adding a flat figure here.
The common mistake
Pricing a hip roof as a bigger roof than a gable
A hipped roof looks bigger and more complicated than a gable, and it is easy to assume it has more surface. Over the same plan, at the same pitch and with the same overhangs, it has exactly the same area, which the calculator's source states and the first variant below shows. What differs is the edges: hips replace rakes, the eave runs all the way round, and there is more cutting along every hip. Measure the area once, then let the edges, not a guess, decide the extra material and the allowance.
Change the job, and see what moves
The same house, with gable ends on the main roof
Main Roof Ends: Gable ends → 1,771 sq ft (164.5 m²)
Give the main block gable ends instead of hips and the area is unchanged at 1,771 sq ft. The edges change completely: the ridge runs the full length at 71 ft, the hips disappear, the eaves shrink to 98 ft and the rakes grow to 87.21 ft. Same shingles, different trim.
The same house, at a steeper pitch
Roof Pitch (rise per 12 run): 8 → 1,904 sq ft (176.9 m²)
Build the same house at a 8/12 pitch and the area rises to 1,904 sq ft, with the hips and valleys lengthening to 87.55 ft and 34.4 ft. The plan is the same; only the slope factor moves, and it moves every sloped length with it.
What to run next
- Roofing Shingle Calculator
Turns the roof area into squares and bundles, with an allowance chosen for a roof with this much hip and valley.
- Roof Ridge Cap Calculator
Counts the cap shingles for the ridges and hips together from their combined length.
- Ice & Water Shield Calculator
Valleys and eaves are lined with a self-adhering membrane where the climate needs it, counted from these lengths.
Sources
The method and every constant behind these figures belong to the L-Shaped and T-Shaped Roof Calculator (Area, Ridges, Hips, Valleys, Eaves and Rakes), version 1.0.0, last verified 2026-10-10. It rests on:
- 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
Frequently asked questions
- How do I calculate the roof area of an L-shaped house?
- Add the plan of the main roof and the wing, measured at the eaves, and multiply by the slope factor for the pitch. For this house that is 1,584 sq ft of plan and 1,771 sq ft on the slope.
- Does a hip roof have more area than a gable roof?
- Not over the same plan and pitch. With gable ends the same house is still 1,771 sq ft; the hips change the edges, not the area.
- How long are the valleys on an L-shaped roof?
- On this house, 2 valleys totalling 33 ft, where the wing's roof meets the main slope.