The rise in inches for every 12 inches of level run, written as x:12. It describes the same slope as an angle in degrees, in different units.

How do I measure pitch without climbing on the roof?

From the attic. Hold a level against a rafter, mark 12 inches along it, and measure straight up from the mark to the rafter. That measurement is the rise.

Can I put asphalt shingles on a 3:12 roof?

Only with double underlayment, under IRC R905.2. Below 2:12, asphalt shingles are not allowed at all. Confirm which code edition your jurisdiction adopted.

Is 4:12 a steep roof?

Not under OSHA 1926.500(b). A steep roof is more than 4 in 12, so exactly 4:12 is still low-slope.

How many degrees is a 6:12 roof?

About 26.6 degrees. The angle is arctan(rise ÷ 12). A 12:12 roof is 45 degrees.

What is the difference between pitch and slope percent?

Pitch is rise over 12. Slope percent is rise divided by run, times 100. A 6:12 roof is a 50% slope.

HyreRoof tools

Roof pitch calculator

Type a rise and run from the attic, or an angle. You get the pitch, degrees, percent slope, area multiplier and rafter length, plus the code line the slope sits on.

4:12 OSHA low-slope limit Under OSHA 1926.500(b) a steep roof is more than 4 in 12. Exactly 4:12 is still low-slope, so do not round it up.

Roof pitch is the rise in inches for every 12 inches of level run. A 6:12 roof rises 6 inches per foot, which is 26.6 degrees and a 1.118× area multiplier. The code lines matter more than the conversion: no asphalt below 2:12, double underlayment below 4:12, and OSHA’s steep-roof rules above 4:12.

Pitch, degrees and the code line

Measure from the attic. Nothing is stored or emailed.

— Pitch

— Angle

— Slope percent

— Surface multiplier

— Rafter length

— Code and OSHA line

What this assumed —

A pitch read from a photo is an estimate. The code line is model code; your jurisdiction may have adopted another edition. HyreRoof does not inspect roofs.

Pitch, angle and area, with the asphalt rule for each

Pitch	Angle	Slope factor	Asphalt shingles under IRC R905.2
1:12	4.8°	×1.003	Not permitted
2:12	9.5°	×1.014	Permitted with double underlayment
3:12	14.0°	×1.031	Permitted with double underlayment
4:12	18.4°	×1.054	Permitted with single underlayment
6:12	26.6°	×1.118	Permitted with single underlayment
8:12	33.7°	×1.202	Permitted with single underlayment
10:12	39.8°	×1.302	Permitted with single underlayment
12:12	45.0°	×1.414	Permitted with single underlayment
16:12	53.1°	×1.667	Permitted with single underlayment

Angle is arctan(rise ÷ 12). Slope factor is √(rise² + 12²) ÷ 12.

Other coverings have their own slope minimums in IRC R905, and manufacturer instructions can be stricter. Check the section for your covering.

Three ways to measure pitch without getting on the roof

From the attic
Hold a level flat against the underside of a rafter. Mark 12 inches along it, then measure straight up from the mark to the rafter. That is the rise.
From a gable photo
Photograph a gable end square-on from the ground and measure rise and run on the photo. The ratio survives the scaling.
With a phone
A phone level app can read an angle. Hold it against a rafter in the attic and pick “an angle in degrees” above.
Never from the roof surface
Every method here works from the ground or the attic. None needs you on the roof.

Pitch is a safety question before it is a geometry one

The federal rule for professional roofers is the best argument against “just get up there and look.”

The line is six feet. 29 CFR 1926.501(b)(13): “Each employee engaged in residential construction activities 6 feet (1.8 m) or more above lower levels shall be protected by guardrail systems, safety net system, or personal fall arrest system unless another provision in paragraph (b) of this section provides for an alternative fall protection measure.”

On a steep roof. 1926.501(b)(11): “Each employee on a steep roof with unprotected sides and edges 6 feet (1.8 m) or more above lower levels shall be protected from falling by guardrail systems with toeboards, safety net systems, or personal fall arrest systems.”

On a low-slope roof. 1926.501(b)(10) allows more combinations, such as a warning line with a safety monitor. It is a wider menu, not an exemption.

Where the line falls. A steep roof under 1926.500(b) is greater than 4 in 12. Exactly 4:12 is still low-slope, and the two sides of that line allow different kinds of fall protection.

What it means for you. OSHA rules bind employers, not homeowners, but the line still applies. A trained roofer may not work above six feet without fall protection. Look from the ground, a window or the attic, or use a photo or a drone.

The code lines a pitch crosses, and what changes on a bid

Pitch is continuous. Its consequences come in steps.

Pitch	What the rule says	What changes on the bid
Below 2:12	No asphalt shingles. “Asphalt shingles shall only be used on roof slopes of two units vertical in 12 units horizontal (17-percent slope) or greater.”	The roof needs a low-slope covering. A bid offering shingles here offers something the model code does not allow.
2:12 to under 4:12	Asphalt with doubled underlayment. Double underlayment is required on slopes between 2:12 and 4:12.	Two layers of underlayment instead of one. If a low-slope plane is priced with one layer, ask why.
4:12 exactly	The OSHA low-slope limit. Exactly 4:12 is still low-slope.	The low-slope fall protection options, such as a warning line with a safety monitor, still apply.
Above 4:12	A steep roof under OSHA 1926.500(b).	Fall protection narrows to guardrails with toeboards, safety nets or personal fall arrest. Expect the bid to account for it.
Above 21:12	Asphalt shingles follow the manufacturer’s steep-slope attachment method.	A special fastening pattern. Ask for it in writing.

This is model code. Adoption and amendment are local, and your jurisdiction may have adopted another edition. Confirm with your building department before relying on it.

The one multiplication that tests a bid

Footprint times slope factor, divided by 100, is squares before waste.

The formula. Slope factor = √(rise² + 12²) ÷ 12, the ratio of roof surface to footprint. A 4:12 roof is ×1.054, a 6:12 roof ×1.118, a 9:12 roof ×1.250 and a 12:12 roof ×1.414.

The check. A 2,000 sq ft footprint at 6:12 is 22.4 squares before waste. A bid well below that has ignored the pitch, and its material order will be short.

Where it goes wrong. A main roof with a porch at another pitch is two calculations. Averaging the pitches gets both wrong. Dormers add surface that a footprint does not show.

Overhangs count. Use the roof’s footprint, eaves included. A 12-inch overhang all round a 40 × 50 ft house adds 184 sq ft before the slope factor.

It is not a waste factor. Offcuts at hips, valleys and rakes come on top. Slope factor first, waste second, as two numbers.

What a bid should say about pitch

The pitch of each plane
Not “the roof.” A porch, extension or dormer at another pitch is its own area and may sit in another code band.
Squares, with waste shown separately
Footprint times slope factor, divided by 100, then a stated waste allowance. Two numbers, because they answer to different things.
Layer count for underlayment below 4:12
Double underlayment is required on slopes between 2:12 and 4:12. A low-slope plane priced with one layer is a pricing error or a spec the code does not permit.
Fall protection on a steep roof
Above 4:12 the crew needs the protection OSHA lists. A bid for a steep roof can reasonably include time and equipment for it.
One area figure for a multi-pitch roof
Averaging pitches gives the wrong area for every plane. Ask how each plane was measured.
Asphalt shingles below 2:12
“Asphalt shingles shall only be used on roof slopes of two units vertical in 12 units horizontal (17-percent slope) or greater.” Ask what low-slope covering the bidder would use instead.

Why a shallow pitch matters at the eave

Shingles shed water by overlap. The flatter the roof, the more work each overlap does.

How water moves on a shallow roof

Water runs off a steep roof faster than a shallow one. On a shallow roof it lingers under each lap longer, and wind or ice can push it sideways or back up the slope.

An ice dam holds a pool of water behind frozen snow at the eave. On a shallow roof that water needs to climb less to reach the next lap. That is why low pitch and an ice-dam climate call for care at the edge.

What the code asks for at that edge

The ice barrier. “In areas where there has been a history of ice forming along the eaves causing a backup of water as designated in Table R301.2, an ice barrier shall be installed” for the listed coverings, extending “not less than 24 inches (610 mm) inside the exterior wall line of the building.”

The drip edge. “A drip edge shall be provided at eaves and rake edges of shingle roofs,” and it “shall extend not less than 1/4 inch (6.4 mm) below the roof sheathing.”

Read at UpCodes in the 2021 IRC as adopted in Maryland, September 5, 2026. Your jurisdiction may have adopted another edition.

Two questions for any bidder

What pitch did you measure, and how did you measure it? How far up the deck does the ice barrier run, measured from inside the wall line?

A bidder who measured can answer both. Neither question needs you to climb.

What this calculator cannot do

The pitch calculator converts the rise and run you give it. Four things are outside what it can know.

It converts the number you give it
A wrong rise makes every output wrong. Measure against a rafter, or on a square-on photo of a gable, and measure twice.
It cannot count your planes
Treating a complex roof as one surface is a measuring problem. No converter fixes it.
It does not know your adopted code
This is model code. Adoption and amendment are local, and your jurisdiction may have adopted another edition. Confirm with your building department before relying on it.
It cannot say whether the frame will carry a heavier covering
Tile and slate weigh more than asphalt. A change of covering can need an engineer. Pitch is one input to that question, not the answer.

HyreRoof does no roofing work, ranks no contractors and takes no referral fee.

Pitch terms that get mixed up

Pitch: Rise over a 12-inch run, written x:12. A ratio, not an angle. More on reading roof pitch.
Slope percent: Rise divided by run, times 100. A 6:12 roof is a 50% slope. If a document says “slope” with no unit, ask which is meant.
Angle: Arctan(rise ÷ 12), in degrees from level. Handy for setting a tool. Code text uses the ratio.
Slope factor: Roof surface over footprint area: √(rise² + 12²) ÷ 12. Exact geometry.
Low-slope roof: Under OSHA 1926.500(b), 4 in 12 or less. The IRC’s asphalt limits sit at 4:12 and 2:12. They are separate rules with separate purposes.
Steep roof: Under OSHA 1926.500(b), more than 4 in 12.
Plane: One continuous roof surface at one pitch. Each needs its own calculation.

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Questions this calculator answers

What is roof pitch?: The rise in inches for every 12 inches of level run, written as x:12. It describes the same slope as an angle in degrees, in different units.
How do I measure pitch without climbing on the roof?: From the attic. Hold a level against a rafter, mark 12 inches along it, and measure straight up from the mark to the rafter. That measurement is the rise.
Can I put asphalt shingles on a 3:12 roof?: Only with double underlayment, under IRC R905.2. Below 2:12, asphalt shingles are not allowed at all. Confirm which code edition your jurisdiction adopted.
Is 4:12 a steep roof?: Not under OSHA 1926.500(b). A steep roof is more than 4 in 12, so exactly 4:12 is still low-slope.
How many degrees is a 6:12 roof?: About 26.6 degrees. The angle is arctan(rise ÷ 12). A 12:12 roof is 45 degrees.
What is the difference between pitch and slope percent?: Pitch is rise over 12. Slope percent is rise divided by run, times 100. A 6:12 roof is a 50% slope.

Sources and methodology

Figures dated September 5, 2026. Last reviewed September 28, 2026.

IRC 2021 R905.2, Asphalt shingles (International Code Council via UpCodes, retrieved September 5, 2026). The 2:12 floor and double underlayment between 2:12 and 4:12. Model code; adoption is local.
IRC 2021 Chapter 9, Roof Assemblies: R903, R905.1.2 ice barriers, R905.2.8.5 drip edge (ICC, 2021 IRC as adopted in Maryland, read at UpCodes, retrieved September 5, 2026). The ice barrier and drip edge text at the eave.
29 CFR 1926.500(b), definitions of steep roof and low-slope roof (OSHA, retrieved August 9, 2026).
29 CFR 1926.501(b), duty to have fall protection (OSHA, read at the Cornell LII mirror, retrieved September 5, 2026). osha.gov did not load for automated retrieval that day, so the text was read at the mirror.

Roofing squares calculator With the multiplier in hand, turn footprint into squares.
Roof replacement cost calculator Squares times the rates on your bid.
Roof material selector Pitch rules some coverings out before price does.
Roof inspection What an inspection looks at, without you climbing.

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