Roof Pitch Calculator
Convert rise and run to roof pitch (x:12), degrees and slope percent, get the pitch multiplier, and turn a footprint into real roof area and squares.
Roof Pitch Calculator: with the default inputs, pitch is 6:12.
Rise & run mode. Vertical distance over the run you measured.
Rise & run mode. Horizontal distance — 12 in gives the pitch directly.
Pitch mode. A 6:12 roof rises 6 in for every 12 in of run.
Angle mode. Roof angle from horizontal.
- Angle
- 26.57 deg
- Slope
- 50%Rise ÷ run × 100.
- Pitch multiplier
- 1.118Multiply footprint area or horizontal rafter run by this to get the sloped length or area.
- Actual roof area
- 1,677 ft²
- Roofing squares
- 16.81 square = 100 ft² of roof surface.
Assumptions
- Roof area assumes a uniform pitch across the footprint; hips, valleys and dormers add waste but not multiplier.
- Roofing squares are surface area only, before waste.
| Pitch | Angle | Slope % | Multiplier | Typical use |
|---|---|---|---|---|
| 1:12 | 4.76 | 8.3 | 1.0035 | Low slope: membrane, standing seam only |
| 2:12 | 9.46 | 16.7 | 1.0138 | Minimum for asphalt shingles (IRC R905.2.2) |
| 3:12 | 14.04 | 25 | 1.0308 | Low slope shingles, double underlayment |
| 4:12 | 18.43 | 33.3 | 1.0541 | Common minimum for standard shingle install |
| 5:12 | 22.62 | 41.7 | 1.0833 | Ranch and contemporary homes |
| 6:12 | 26.57 | 50 | 1.118 | Most common residential pitch |
| 7:12 | 30.26 | 58.3 | 1.1577 | Colonials, easy to walk |
| 8:12 | 33.69 | 66.7 | 1.2019 | Steeper colonials; walkable with care |
| 9:12 | 36.87 | 75 | 1.25 | Craftsman, Tudor |
| 10:12 | 39.81 | 83.3 | 1.3017 | Steep — roof jacks needed |
| 12:12 | 45 | 100 | 1.4142 | 45°; Cape Cod, A-frame, Gothic |
| 18:12 | 56.31 | 150 | 1.8028 | Very steep; chalet, church |
How this is worked out
The formula
Pitch (x:12) = rise ÷ run × 12 Angle = arctan(rise ÷ run) Slope % = rise ÷ run × 100 Pitch multiplier = √(1 + (rise ÷ run)²) = √(12² + x²) ÷ 12 Actual roof area = footprint area × pitch multiplier Rafter length = horizontal run × pitch multiplier
Open How it’s calculated above to see this worked through with your own numbers.
What you enter
- Start from
- Choose one of 3 options.Rise and run (measured) · Pitch (x in 12) · Angle in degrees
- Rise
- Rise & run mode. Vertical distance over the run you measured.in in, ft, cm, mm, m · 0 or more · defaults to 6
- Run
- Rise & run mode. Horizontal distance — 12 in gives the pitch directly.in in, ft, cm, mm, m · 0 or more · defaults to 12
- Pitch (rise per 12 in of run)
- Pitch mode. A 6:12 roof rises 6 in for every 12 in of run.from 0 to 48 · defaults to 6
- Angle
- Angle mode. Roof angle from horizontal.from 0 to 89.9 · defaults to 26.57
- Horizontal roof area (footprint)(under More options)
- Area the roof covers as seen from above, including overhangs. Multiplied by the pitch factor to get actual surface area.in ft², m² · 0 or more · defaults to 1500
What you get back
- Pitchmain answer
- Angle
- Slope
- Rise ÷ run × 100.
- Pitch multiplier
- Multiply footprint area or horizontal rafter run by this to get the sloped length or area.
- Actual roof area
- Roofing squares
- 1 square = 100 ft² of roof surface.
What this assumes
- Roof area assumes a uniform pitch across the footprint; hips, valleys and dormers add waste but not multiplier.
- Roofing squares are surface area only, before waste.
About this calculator
In the US, roof slope is written as inches of rise per 12 inches of horizontal run — a "6:12" or "6/12" roof climbs 6 in for every foot it runs. Elsewhere and in engineering it's degrees or percent. This calculator converts between all three from whatever you measured, and gives you the pitch multiplier that turns a footprint into real roof area for ordering shingles, underlayment and ice barrier.
Measuring pitch on a real roof
- From the attic: hold a level horizontally against the underside of a rafter, mark 12 in along the level, and measure straight up (or down) from the mark to the rafter. That measurement is the pitch in x:12 directly.
- On the roof: same thing with a level on the shingles, keeping the level clear of shingle bumps. A 12-in torpedo level is ideal.
- From the ground: a phone inclinometer app held against the gable trim gets you within a degree; enter it in Angle mode.
- From the gable end: measure the total rise and the total run (half the building width for a symmetrical gable) and enter both — units don't matter as long as they're the same.
Why the multiplier matters
A roof's surface is always larger than the area it covers. The factor is √(rise² + run²) ÷ run: 1.054 at 4:12, 1.118 at 6:12, 1.202 at 8:12 and 1.414 at 12:12. Roofers take the footprint from the plans or a satellite measurement, multiply by the pitch factor, then add 10–15% for waste and the starter/ridge courses. Enter the footprint under More options to get the surface area and the number of roofing "squares" (100 sq ft each).
The same multiplier gives rafter length from horizontal run: a 14-ft run at 6:12 needs a 15.65-ft rafter before the overhang and ridge deduction.
Code and material limits
The IRC allows asphalt shingles down to 2:12, with two layers of underlayment between 2:12 and 4:12 (R905.1.1, R905.2.2). Below 2:12 you need a low-slope system. Clay and concrete tile need 2½:12 minimum; wood shakes 3:12 or 4:12 depending on type. Most standing-seam metal can go to ½:12 with sealed seams. Steeper than about 8:12 is not walkable without roof jacks, and labor quotes go up accordingly.
Frequently asked questions
▸What angle is a 6/12 roof pitch?
26.57°. Divide 6 by 12 to get 0.5 and take the arctangent. A 4/12 is 18.43°, 8/12 is 33.69° and 12/12 is exactly 45°.
▸What is the pitch multiplier and how do I use it?
It's the ratio of sloped length to horizontal length, √(1 + (rise/run)²). Multiply the roof's footprint area by it to get actual roof area — a 1,500 sq ft footprint at 6/12 is 1,677 sq ft of roofing.
▸What is the minimum roof pitch for shingles?
2:12 under the International Residential Code (R905.2.2). Between 2:12 and 4:12, two layers of underlayment are required. Below 2:12 use a membrane or metal system rated for low slope.
▸How do I convert roof pitch to percent slope?
Divide rise by run and multiply by 100. A 6:12 roof is 50% slope; a 12:12 is 100%. Percent slope is common on plans for drainage and site work.
▸Is roof pitch the same as slope?
In everyday use, yes. Strictly, pitch is rise over total span (a 6:12 slope on a symmetrical gable is a 1/4 pitch) and slope is rise over run. Modern practice, and this calculator, use x:12 rise over run.
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