How do I convert roof pitch to degrees?

Use the formula: angle = arctan(rise/run). For a 6/12 pitch: arctan(6/12) = arctan(0.5) = 26.57 degrees. Common conversions: 4/12 = 18.43 degrees, 6/12 = 26.57 degrees, 8/12 = 33.69 degrees, 12/12 = 45 degrees.

What is a good roof pitch for a house?

The most common residential roof pitch is 4/12 to 6/12 (18 to 27 degrees). Pitches below 2/12 require a flat roof membrane system. Pitches above 9/12 are steep slope and require safety measures during installation.

How do I calculate rafter length from roof pitch?

Rafter length = half-span divided by cos(angle). For a 6/12 pitch (26.57 degrees) with a 12-foot half-span: rafter = 12 / cos(26.57) = 13.42 feet. Add overhang to the half-span before calculating if rafters extend beyond the wall plate.

What is the minimum roof pitch for shingles?

Most asphalt shingle manufacturers require a minimum pitch of 2/12 (about 9.5 degrees). Pitches between 2/12 and 4/12 require two layers of underlayment. Below 2/12 requires a flat roof membrane system.

Roof Pitch Calculator – Chart, Angle & Slope Converter

Unit system

Quick presets

Click a preset to populate the pitch field instantly.

Rise (in)

Vertical increase.

Run (in)

Horizontal distance (default 12 in / 1 m).

Pitch (X/12)

Rise per 12 in run.

Angle (°)

Slope (%)

Precision

Rafter length & roof area (optional)

Half-span (ft)

Wall plate to ridge — required for rafter length.

Overhang / eave (ft)

Horizontal add-on beyond the wall plate.

Roof length (ft)

Ridge length — needed for roof area.

Building span (ft)

Total width wall-to-wall — needed for roof area.

Roof Triangle Diagram

Diagram is illustrative based on your rise/run. Not for code-compliance drawings.

Roof Pitch Chart — All Common Pitches

Reference chart converting all standard roof pitches to degrees, slope percentage, pitch factor, and rafter length per foot of run.

Pitch (X/12)	Angle (°)	Slope %	Pitch factor	Rafter per 12" run	Category
1/12	4.76°	8.3%	1.003	12.04"	Flat / low slope
2/12	9.46°	16.7%	1.014	12.17"	Low slope
3/12	14.04°	25.0%	1.031	12.37"	Low slope
4/12	18.43°	33.3%	1.054	12.65"	Standard residential
5/12	22.62°	41.7%	1.083	13.00"	Standard residential
6/12	26.57°	50.0%	1.118	13.42"	Most common
7/12	30.26°	58.3%	1.158	13.89"	Standard residential
8/12	33.69°	66.7%	1.202	14.42"	Standard residential
9/12	36.87°	75.0%	1.250	15.00"	Steep slope
10/12	39.81°	83.3%	1.302	15.62"	Steep slope
11/12	42.51°	91.7%	1.357	16.28"	Steep slope
12/12	45.00°	100.0%	1.414	16.97"	Steep slope

Highlighted rows are the most common residential pitches. Pitch factor = √(rise² + 12²) ÷ 12. Rafter per 12" run = pitch factor × 12".

Roof Pitch Categories

Category	Pitch range	Angle range	Typical use	Shingle compatible?
Flat / low slope	0/12–2/12	0°–9.5°	Commercial flat roofs	No — requires membrane
Low slope	2/12–4/12	9.5°–18.4°	Some residential, additions	With special underlayment
Standard residential	4/12–9/12	18.4°–36.9°	Most US homes	Yes — standard installation
Steep slope	9/12–12/12	36.9°–45°	Cape Cod, Tudor, steep gables	Yes — with safety precautions
Very steep / mansard	12/12+	45°+	Mansard, very steep gables	Yes — specialty installation

Roof Pitch Guide — Angle, Slope & Rafter Length

Roof pitch describes how steeply a roof slopes. In the US it is expressed as rise-over-run, the number of inches the roof rises for every 12 inches of horizontal run. A 6/12 pitch is one of the most common residential pitches and produces a classic looking home.

How to calculate roof pitch

Angle (°) = arctan(rise ÷ run) — e.g. arctan(6÷12) = 26.57°
Slope % = (rise ÷ run) × 100 — e.g. (6÷12) × 100 = 50%
Pitch factor = √(rise² + 12²) ÷ 12 — used to convert plan area to roof surface area
Rafter length = half-span ÷ cos(angle) — or half-span × pitch factor ÷ 12 in imperial

What pitch factor means

The pitch factor converts a roof's plan (footprint) area to its actual sloped surface area. A 6/12 pitch has a factor of 1.118, meaning the actual roof surface is 11.8% larger than the footprint. This is important for ordering shingles, underlayment, and metal roofing. Always order based on the sloped area, not the footprint.

Frequently Asked Questions

Roof pitch is a ratio describing how steep a roof is. In the US it is written as X/12, the number of inches the roof rises for every 12 inches of horizontal run. A 6/12 pitch means 6 inches of rise per 12 inches of run, producing a 26.57° angle. See the roof pitch chart above for all common conversions.

Use the formula: angle = arctan(rise ÷ 12). Common conversions: 4/12 = 18.43°, 6/12 = 26.57°, 8/12 = 33.69°, 12/12 = 45°. Enter the pitch in the calculator above and it converts instantly, or use the roof pitch chart on this page.

The most common residential pitches are 4/12 to 6/12 (18° to 27°). These offer a good balance of aesthetics, drainage, and ease of installation. Pitches below 2/12 require a membrane roof system. Pitches above 9/12 are steep and require additional safety equipment during installation.

Rafter length = half-span × pitch factor (or half-span ÷ cos(angle)). For a 6/12 pitch with a 12-foot half-span: rafter = 12 × 1.118 = 13.42 feet. Add overhang length to the half-span before calculating if your rafters extend beyond the wall plate. The calculator above handles this automatically.

They are related but different. Slope % = (rise ÷ run) × 100. A 6/12 pitch = 50% slope. A 12/12 pitch = 100% slope. Slope percentage is common in civil engineering; the X/12 pitch ratio is the US roofing standard. The calculator converts between both.

Most asphalt shingle manufacturers require a minimum pitch of 2/12 (~9.5°). Pitches from 2/12 to 4/12 require two layers of underlayment per most building codes. Below 2/12 requires a flat roof membrane system, standard shingles cannot be used.

Roof Planning Checklist

Reviewed by Caleb Wright. Covers pitch measurement, rafter sizing, underlayment requirements, flashing, ventilation, and safety requirements before ordering materials.

Download Checklist (PDF)

Planning reference only. See Methodology and Data Sources. View all project checklists →

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Accuracy & Review

Reviewed by: Caleb Wright

Caleb validates our roofing calculators, reviewing pitch factor formulas, rafter length calculations, and waste factor guidance to ensure estimates reflect real-world installation conditions.

Last updated: Feb 12, 2026

See: Methodology · Data Sources · Review Board

Disclaimer: Results are preliminary estimates only and do not replace professional roofing specifications. Rafter lengths and roof areas may vary based on roof style, framing details, and local code requirements.

See Methodology and Data Sources for calculation details.