It is the everyday pitch of North American houses: steep enough to shed rain and snow well and leave a usable attic, still gentle enough to walk with care and to shingle without staging. The calculator is preset to a 6/12 gable; enter the building width and overhang to size the rafters.
How to use this calculator
- Enter the width of the building across the rafters, measured to the outside of the walls.
- Leave the pitch as it is, or type another to see how the rafter length changes.
- Enter the eave overhang, measured level from the wall.
- The result gives the rafter length with and without the overhang, and how high the ridge rises above the walls.
Worked examples
A two-car garage
Building width: 24 ft · Pitch: 6 in 12 · Overhang: 12 in
- Rafter length
- 14.53 ft
- Without overhang
- 13.42 ft
- Ridge height above the wall
- 72.0 in
- Run
- 12.00 ft
A two-story house
Building width: 32 ft · Pitch: 6 in 12 · Overhang: 18 in
- Rafter length
- 19.57 ft
- Without overhang
- 17.89 ft
- Ridge height above the wall
- 96.0 in
- Run
- 16.00 ft
A garden shed with a loft
Building width: 12 ft · Pitch: 6 in 12 · Overhang: 8 in
- Rafter length
- 7.45 ft
- Without overhang
- 6.71 ft
- Ridge height above the wall
- 36.0 in
- Run
- 6.00 ft
Rafter length on a 6/12 roof by building width and overhang
| Building width | 0 in | 12 in | 18 in | 24 in |
|---|---|---|---|---|
| 12 ft | 6.71 | 7.83 | 8.39 | 8.94 |
| 16 ft | 8.94 | 10.06 | 10.62 | 11.18 |
| 20 ft | 11.18 | 12.30 | 12.86 | 13.42 |
| 24 ft | 13.42 | 14.53 | 15.09 | 15.65 |
| 28 ft | 15.65 | 16.77 | 17.33 | 17.89 |
| 32 ft | 17.89 | 19.01 | 19.57 | 20.12 |
| 36 ft | 20.12 | 21.24 | 21.80 | 22.36 |
Each cell: the rafter length along its top edge from the wall to the ridge plus the overhang, for a gable roof with the ridge in the middle. Buy the next stock length up.
Why 6/12 is the default pitch
Builders reach for 6/12 because it balances cost and performance. Rain runs off quickly, snow slides rather than piling up, and standard shingles go on with one layer of underlayment, since the slope is well past 4 in per 12 in. Rafters stay a manageable length, and trusses in this pitch are stock items at most yards. The ridge rises a quarter of the building's width above the walls, which leaves a walkable attic in the middle of a house.
Working on a 6/12 roof
Roofers walk a 6/12 roof, but it is the steepest pitch most people find comfortable, and dew or dust makes it slippery. Toe boards or roof jacks help when you carry bundles, and a harness tied to a ridge anchor is cheap insurance. Each roofing square covers 100 sq ft of surface, so the multiplier matters when you order: the roofing calculator applies it from your plan dimensions.
Comparing it with a lower pitch
Against a 4/12 roof, a 6/12 one has longer rafters, a taller attic and more roof surface for the same house, so it costs somewhat more in material. It also looks more traditional from the street. Use the rafter calculator to compare any two pitches on your own building width.
Common questions
What angle is a 6/12 pitch?
26.6 degrees, a slope of 50 percent.
Is a 6/12 roof walkable?
Yes, for most roofers and careful homeowners in dry conditions. It is near the upper limit of comfortable walking, so use soft-soled shoes and fall protection.
What is the slope multiplier for a 6/12 roof?
1.118. A roof that covers a flat area of one roofing square has that many squares of surface.
How high is the ridge on a 6/12 roof?
It rises a quarter of the building's width above the top of the walls, before the rafter depth. Enter your width above; the result shows the ridge height.