Roof Pitch Calculator

Enter your roof’s rise and run below to convert between the three ways roof slope gets expressed (rise/run ratio, degrees, and percent) and see the area multiplier for material estimating.

Rise (in per 12 in run)

Pitch

6/12

Degrees

26.57°

Percent

50.0%

Area multiplier

×1.118

Every 1,000 sq ft of building footprint = ~1118 sq ft of actual roof surface at this pitch.

Need to know how many shingles or squares to order? Use our roofing calculator instead. This page is about the angle itself and which materials it allows.

Three Ways to Express the Same Slope

Format	How It’s Written	Where You’ll See It
Rise/run (pitch)	e.g. 6/12	Roofing contractors, framers, shingle specs (the North American standard)
Degrees	e.g. 26.57°	Architects, structural engineers, international codes, CAD software
Percent	e.g. 50%	Civil engineering, site grading, some European codes

Rise/run means how many inches the roof climbs vertically for every 12 inches of horizontal run. A 6/12 roof rises 6 inches over each 12-inch stretch.

Converting to degrees: Degrees = arctan(rise ÷ 12)

Converting to percent: Percent = (rise ÷ 12) × 100

Every Common Pitch, Converted

The area multiplier column is the one most people miss. It’s what converts your building’s flat footprint into actual roof surface area for ordering material.

Pitch	Degrees	Percent	Area Multiplier	Notes
1/12	4.76°	8.3%	1.003	Low-slope; membrane roofing only
2/12	9.46°	16.7%	1.014	Absolute minimum for shingles, with double underlayment
3/12	14.04°	25.0%	1.031	Still low-slope for shingle purposes
4/12	18.43°	33.3%	1.054	Standard minimum for regular shingle installation
5/12	22.62°	41.7%	1.083	Common on ranch and starter homes
6/12	26.57°	50.0%	1.118	Most common residential pitch in North America
7/12	30.26°	58.3%	1.158	Walkable for most experienced roofers
8/12	33.69°	66.7%	1.202	Roughly the practical limit for walking without staging
9/12	36.87°	75.0%	1.250	Steep-slope; safety harnesses typically required
10/12	39.81°	83.3%	1.302	Requires roof jacks or scaffolding
11/12	42.51°	91.7%	1.357	Steep; professional installation strongly advised
12/12	45.00°	100.0%	1.414	A perfect 45° angle
14/12	49.40°	116.7%	1.537	Common on Tudor and steep gable designs
16/12	53.13°	133.3%	1.667	Architectural / accent roofs
18/12	56.31°	150.0%	1.803	Very steep; specialty installation
20/12	59.04°	166.7%	1.944	Approaching near-vertical territory
24/12	63.43°	200.0%	2.236	Roof surface is more than twice the footprint

Converting Degrees Back to Pitch

Architectural drawings, CAD exports, and most non-US specifications give the angle in degrees, but lumber yards and shingle manufacturers work in rise/run. Going the other direction uses rise = 12 × tan(angle):

Degrees	Exact Pitch	Nearest Standard Pitch
5°	1.05/12	1/12
10°	2.12/12	2/12
15°	3.22/12	3/12
20°	4.37/12	4/12
22.5°	4.97/12	5/12
25°	5.60/12	6/12
30°	6.93/12	7/12
35°	8.40/12	8/12
40°	10.07/12	10/12
45°	12/12	12/12
50°	14.30/12	14/12

Note that a 30° roof is not a 6/12. It’s 6.93/12, closer to 7/12. Rounding a specified angle to the nearest familiar pitch can throw off rafter lengths by several inches over a long run, so frame from the exact figure and use the rounded pitch only when talking to suppliers.

How Pitch Determines Your Material Options

This is the part that actually matters for planning a project. Not every roofing material works at every slope:

• Below 2:12. Standard shingles are not permitted by any major manufacturer or the IRC. You need a continuous low-slope membrane system (TPO, EPDM, or modified bitumen).
• 2:12 to 4:12. This range is considered low-slope for shingles. The IRC requires double-layer ice-and-water underlayment covering the full deck, not the standard single-layer felt.
• 4:12 and above. This is the standard minimum for regular asphalt shingle installation per IRC R905.2 and major manufacturer warranties (GAF, CertainTeed, Owens Corning).
• Above 4:12. OSHA classifies this as “steep-slope” for fall-protection purposes, meaning harnesses and additional safety equipment are typically required for installers.
• Above 6:12. Many insurers won’t cover DIY roofing work at this pitch or steeper; professional installation becomes both safer and often necessary for warranty and insurance purposes.

Once the pitch is settled and the material is allowed at that slope, the quantity question is separate: squares, bundles, and the linear-foot items that scale with roof shape instead of area. The roofing calculator takes the pitch multiplier from this page and turns a footprint into an order.

Why Pitch Affects Your Material Order

A steeper roof isn’t just harder to walk on. It also has more actual surface area than its footprint suggests, because the sloped plane is longer than the flat area beneath it. The multiplier is:

Area Multiplier = √(1 + (rise ÷ 12)²)

At 6/12, that’s about 1.118, meaning every 1,000 sq ft of building footprint corresponds to roughly 1,118 sq ft of actual roof surface you need to cover. Skip this step and calculate materials from footprint alone, and you’ll come up short by 5% on a 4/12, 41% on a 12/12, and more than 120% on a 24/12. The error compounds quickly, which is why the multiplier column in the table above matters more than the angle itself for anyone ordering material.