How to measure a roof pitch
Stay off the roof if you can. The attic gives you the same number. Hold a level against the underside of a rafter so it sits flat, mark 12 inches along the level, then measure straight up from that mark to the rafter. That measurement is your rise per 12, and it is the same pitch as the roof above.
With no attic access, look for the building plans, an old roofing quote or an inspection report. You can also work from a photo taken square on to the gable, by measuring the rise and half the width on the picture itself. The ratio holds at any scale, and it is good enough for planning.
Measure the footprint from the ground, and include the overhangs, since those carry shingles too. Do not use the house's floor area. If different parts of the roof have different pitches, measure each as its own plane, as the IKO guide does.
A worked example
This one is printed in IKO's estimating guide: a roof with one plane of 1,302 square feet at 9 in 12, and another of 643 square feet at 6 in 12. These lines come from the same formula the calculator above runs.
IKO's two-plane roof
- 9 in 12 multiplier: 1.250
- 1,302 × 1.250 = 1627.5 sq ft
- 6 in 12 multiplier: 1.118
- 643 × 1.118 = 718.9 sq ft
- Total: 2347 sq ft of roof
IKO gets the same 2347 square feet from its printed table, then adds 10 percent for waste. To turn that into bundles, take the area to the roofing calculator. If the walls are being re-covered too, the siding calculator takes the same pitch for its gables.
Roof pitch conversions
Whole-number pitches from a low shed to a steep gable. Rows up to 4 in 12 are low slope under OSHA's definition, and IKO treats 2 to 4 in 12 as low slope for shingles too.
| Pitch | Degrees | Slope | Multiplier |
|---|---|---|---|
| 2 in 12 | 9.46 | 16.7% | 1.014 |
| 3 in 12 | 14.04 | 25.0% | 1.031 |
| 4 in 12 | 18.43 | 33.3% | 1.054 |
| 5 in 12 | 22.62 | 41.7% | 1.083 |
| 6 in 12 | 26.57 | 50.0% | 1.118 |
| 7 in 12 | 30.26 | 58.3% | 1.158 |
| 8 in 12 | 33.69 | 66.7% | 1.202 |
| 9 in 12 | 36.87 | 75.0% | 1.250 |
| 10 in 12 | 39.81 | 83.3% | 1.302 |
| 12 in 12 | 45.00 | 100.0% | 1.414 |
Mistakes that give the wrong pitch
- Mixed units. A rise in inches over a run in feet gives a nonsense answer. Measure both in inches.
- Pitch against span. Older texts write pitch as rise over the whole span, not the run, so a 1/4 pitch and a 6 in 12 slope are the same roof. IKO warns about exactly this.
- One multiplier for a mixed roof. A multiplier is right only for the plane with that pitch.
- Leaving out the overhang. The footprint is the area under the roof, not under the walls.
- Treating a number as permission. Whether a roof can be walked on depends on surface, weather and footwear, and no chart decides that.
Questions
What is a 6/12 pitch in degrees?
A 6/12 pitch is 26.57 degrees. It rises 6 inches for every 12 across, which is a 50 percent slope, and it has a pitch multiplier of 1.118.
What angle is a 4/12 roof pitch?
A 4/12 roof pitch is 18.43 degrees, or a 33.3 percent slope. It is also the line where OSHA's definition changes: above 4 in 12 is steep, and at or below it is low slope.
What is a roof pitch multiplier?
It is the number you multiply a roof's flat footprint by to get its true sloped area. A 6/12 roof has a multiplier of 1.118, so a 1,000 square foot footprint is about 1,118 square feet of roof.
Can you shingle a 3/12 pitch roof?
Often yes, with extra care. IKO says 2:12 has traditionally been the absolute minimum for asphalt shingles, and treats 2:12 to 4:12 as low slope, while 4:12 is the usual lowest for a standard installation. Some shingles ask for more, so read the label and your local code.
What roof pitch is walkable?
No code or manufacturer we read sets a walkable limit, so we will not give one. It depends on the surface, the weather and your footing. OSHA calls anything over 4 in 12 steep for fall protection. Measure from the attic or from plans if you can.
How do I find my roof pitch without climbing up?
Measure from the attic. Hold a level against the underside of a rafter, mark 12 inches along it, and measure straight up to the rafter. That measurement is your rise per 12. Building plans or a roofer's report may also state it.
This roof pitch is a planning estimate from the numbers you entered, and a slope measured from the attic or a plan is safer than one measured on the roof. A pitch reading does not make a roof safe to walk on. Check the minimum slope on the shingle label, and confirm what your supplier and local code allow.
Sources and review
- Estimating how much roofing is required, IKO, no date printed, file dated 2013.
- Minimum slope for an asphalt shingle roof, IKO, 2023.
- 29 CFR 1926.500, fall protection definitions, Occupational Safety and Health Administration, current text, read November 2026.
Checked in November 2026. Spotted a wrong number? Report it and it goes in the corrections log.
How this is calculated
Every figure below is read from the code that produces the answer, so what is written here is what the calculator ran. The constants were last checked against their sources in November 2026.
The arithmetic
Angle
Angle = arctangent(Rise ÷ Run)
- Rise
- How far the roof goes up
- Run
- How far it goes across, in the same unit
Worked through: arctangent(6 ÷ 12) = 26.57 degrees
Pitch multiplier
Multiplier = √(1 + (Rise ÷ Run)²)
- Multiplier
- What to multiply a footprint by to get the sloped area
Worked through: √(1 + 0.25) = 1.118
True roof area
Roof area = Footprint × Multiplier
- Footprint
- Horizontal area, in square feet
Worked through: 643 × 1.118 = 719 sq ft
The constants, and where they come from
OSHA_STEEP_ABOVE
Published figureThe rise per 12 above which OSHA calls a roof steep
Applies to: Fall protection on construction work. It is not a rule about who can walk on what
Source: 29 CFR 1926.500, fall protection definitions, Occupational Safety and Health Administration, published 2026, read 2026-11.
29 CFR 1926.500 defines a steep roof as a slope greater than 4 in 12, and a low-slope roof as 4 in 12 or less.
SHINGLE_ABSOLUTE_MINIMUM
Published figureThe rise per 12 traditionally considered the minimum for asphalt shingles
Applies to: Asphalt shingles. Some products ask for more, so read the label
Source: Minimum slope for an asphalt shingle roof, IKO, published 2023, read 2026-11. This source is about 3 years old, and it is the one the figure rests on.
IKO says 4:12 is most commonly considered the lowest slope for a standard installation, and that 2:12 to 4:12 is low slope.
DEGREES_PER_RADIAN
DefinitionalDegrees in one radian
Applies to: Definitional, everywhere
True by definition, so there is nothing to cite. The derivation is below.
A half turn is 180 degrees or pi radians, so one radian is 180 divided by pi, about 57.3 degrees.
INCHES_OF_RUN
DefinitionalThe run a pitch is stated against, in inches
Applies to: Definitional, everywhere
True by definition, so there is nothing to cite. The derivation is below.
A pitch of 6 in 12 means 6 inches of rise over 12 inches of run, by the way the trade writes it.
What the labels mean
- Published figure:
- taken directly from the source named beside it.
- Definitional:
- true by definition, like the number of inches in a foot, so there is nothing to cite.
If a figure here looks wrong, it may be. Tell us what you found and we will check it against the source and publish a correction if it needs one. How constants are chosen and how often they are reviewed is set out in our methodology.
How to use the roof pitch calculator
- 1
Choose whether you know the rise and run, or the angle
- 2
Enter them, in the same unit
- 3
Read the pitch, angle, slope and multiplier
- 4
Enter the footprint for the true area of a roof plane
- 5
Take that area to the roofing calculator to size the shingles
What this calculator assumes
Every estimate here rests on the assumptions below. Where your job differs from one of them, the figure will differ too.
- The roof area is right only when the whole footprint shares one pitch. Split a mixed roof into planes
- The footprint is the horizontal area under the roof, including the overhangs
- Rise and run are measured in the same unit
- This roof plane is flat, with no valleys, hips or dormers
Pro tips
- Measure from the attic, not from the roof
- Split a roof into planes when more than one pitch is involved
- Read the minimum slope on the shingle wrapper before planning a low roof