What is 6/12 pitch in degrees?

26.57 degrees. A 6/12 roof rises 6 inches over 12 inches of run, which is arctan(6 divided by 12), or 26.57 degrees off horizontal. Its slope factor is 1.118 and the grade is 50 percent.

What is a roof slope factor?

The number you multiply a roof's footprint area by to get its actual sloped surface area. It is the square root of one plus the pitch ratio squared: 1.054 at 4/12, 1.118 at 6/12, 1.414 at 12/12. Skipping it under-orders shingles.

How do you measure roof pitch?

Hold a level against the roof, mark 12 inches along it from the roof end, and measure straight down to the surface. A 6 inch drop is 6/12. From the attic, read the rise of one rafter over 12 inches of run.

What roof pitch can you walk on?

Up to about 6/12, most roofers walk it directly. From 7/12 to 9/12 you want roof jacks. Past 9/12 it is fall-protection work, and both waste and labor run higher.

MATERIALFOREMAN · SHEET R-002 · ROOF WORKS

CALC-002 · DRAWING NO. R-002 · REV A

Roof pitch calculator.

Drafted to scale · cited sources · honest numbers

Pick a pitch and read the slope angle in degrees, the slope factor that converts plan area to roof area, the percent grade, and the rafter length over a given run. The slope factor is the same number the roofing material calculator uses to size shingles.

◈ DRAFTING PANEL · ROOFING TAKEOFF · N.T.S. SHEET R-002 · REV A

Redline · scope notice Pitch geometry only. Gives rafter length, not rafter size. Sizing a rafter for span, load, and species is engineered work. See the AWC span tables or a licensed engineer before cutting structural members.

Note 01 · Field Procedure

How to find your pitch

Hold a level against the roof or a rafter, running uphill, and bring it to level.
Measure 12 inches along the level from the end that touches the roof, and mark it.
Measure straight down from that 12 inch mark to the roof surface. The drop in inches is the pitch: a 6 inch drop is 6/12.
From inside the attic, the same reading comes off one rafter: its vertical rise over 12 inches of horizontal run.
For rafter length, enter the run, the horizontal distance from the wall plate to the ridge. On a symmetric gable that is half the building width.

Note 02 · Equation

The formula

angle = arctan( rise ÷ 12 ) · factor = √( 1 + ( rise ÷ 12 )² )

riserise in inches per 12 inches of run (the X in X/12)

factorslope factor: multiply plan (footprint) area by this for roof surface area

gradepercent grade is rise ÷ 12 × 100

rafterrafter length is run × slope factor

Slope factor matches the roofing material calculator. A 6/12 roof is 26.57°, factor 1.118, 50 percent grade.

Note 03 · Sanity Ranges

Common pitches

T	Use case	Notes
2/12	Minimum for asphalt shingles	Double underlayment required below 4/12. Below 2/12, go to a membrane.
4/12	Low conventional	Walkable, standard install. 18.43°, factor 1.054.
6/12	Most common residential	26.57°, factor 1.118, 50 percent grade.
12/12	Steep	45°, factor 1.414. Roof jacks and fall protection.

Note 04 · References

Sources

Authorities cited on this sheet

IRC R905.2 Asphalt Shingles · 2021 International Residential Code, free public viewer at ICC. Sets the 2:12 minimum slope for asphalt shingles and the double-underlayment requirement from 2:12 up to 4:12.
ARMA Residential Asphalt Roofing Manual · Asphalt Roofing Manufacturers Association. Free manual covering slope, pitch, and the roof-area method behind the slope factor.

Note 05 · Field Manual

What the sheet count does not tell you

Reading a 6/12 roof

A 6/12 pitch rises 6 inches for every 12 inches of run. That works out to 26.57 degrees off horizontal, a slope factor of 1.118, and a 50 percent grade. The angle is the number people picture; the slope factor is the number that orders material.

Take a gable with a 30 by 40 foot footprint. The plan area is 1,200 square feet, but the roof is not flat. Multiply by the 1.118 slope factor and the actual roof surface is about 1,342 square feet, before waste. Skip the factor and you order 142 square feet short, more than a square of shingles. On a 30 foot wide gable, each common rafter runs 15 feet of run times 1.118, about 16 feet 9 inches, before the ridge and overhang adjustments.

Slope factor is the number that orders shingles

Roof area is never the footprint. A steeper roof has more surface over the same ground, and the slope factor is exactly how much more. It is the roof length up the slope divided by the horizontal run, which is the square root of one plus the pitch ratio squared. At 4/12 it is 1.054, a 5 percent bump. At 12/12 it is 1.414, a 41 percent bump. The shingle calculator applies this same factor automatically; this page exists to show the number and the angle behind it.

Walkable, steep, and low-slope

Up to about 6/12, most crews walk the roof in soft-soled boots and skip the staging. From 7/12 to 9/12 the footing gets dicey and roof jacks earn their keep. Past 9/12 it is fall-protection territory, and waste and labor both climb because every cut and every bundle has to be controlled on the slope.

The other end matters more for code. Asphalt shingles are not permitted below 2/12, and from 2/12 up to 4/12 the IRC requires double underlayment because wind drives rain back up a shallow slope. Below 2/12 the answer is a membrane, not shingles.

Note 06 · Common Questions

Common questions

What is 6/12 pitch in degrees?: 26.57 degrees. A 6/12 roof rises 6 inches over 12 inches of run, which is arctan(6 divided by 12), or 26.57 degrees off horizontal. Its slope factor is 1.118 and the grade is 50 percent.
What is a roof slope factor?: The number you multiply a roof's footprint area by to get its actual sloped surface area. It is the square root of one plus the pitch ratio squared: 1.054 at 4/12, 1.118 at 6/12, 1.414 at 12/12. Skipping it under-orders shingles.
How do you measure roof pitch?: Hold a level against the roof, mark 12 inches along it from the roof end, and measure straight down to the surface. A 6 inch drop is 6/12. From the attic, read the rise of one rafter over 12 inches of run.
What roof pitch can you walk on?: Up to about 6/12, most roofers walk it directly. From 7/12 to 9/12 you want roof jacks. Past 9/12 it is fall-protection work, and both waste and labor run higher.

PROJ MATERIALFOREMAN

SHT R-002 / 014

REV A · 2026-06-07

DRAWN MF