Quick answer
Roof pitch is how many inches the roof rises for every 12 inches it runs horizontally. In the attic, mark 12 inches from one end of a level, touch that end to the underside of a rafter and hold the level perfectly level, then measure straight up or down from that mark to the rafter: that number is the pitch. A phone level reads degrees instead; pitch = 12 × tan(angle), so 26.6° is a 6/12 roof.
What "6/12" means
The building code states every roof slope as units of rise in 12 units of run, so a 6/12 roof climbs 6 inches for each foot it covers horizontally. Many people, and our calculators, call that number the pitch. InterNACHI, the home inspectors' association, calls it slope and keeps "pitch" for rise divided by the full span, so by its definition a 4-in-12 slope is a 1/6 pitch. If a contractor quotes a fraction like 1/4 or 1/3, ask which they mean.
Three ways to measure it
- From the attic. InterNACHI's method: mark 12 inches from one end of a level, hold that end against the bottom edge of a rafter, keep the level perfectly level, and measure vertically from the 12-inch mark to the rafter. That measurement is the rise per 12 inches of run.
- From a rake board, on a ladder. The same level-and-tape method works against the sloped trim board at a gable end. InterNACHI notes that measuring on the roof surface itself may not be the most accurate, because the roof covering is uneven.
- With a phone. The iPhone Measure app has a level that shows how many degrees a surface is off level, which Apple describes as approximate. Hold it along a rafter in the attic and convert the angle with pitch = 12 × tan(angle), or use the table below. On other phones, a level or angle app that reads degrees works the same way.
Whichever you use, stay off the roof. The Consumer Product Safety Commission warns that ladder falls can cause injuries "ranging from bruises to fractures, and even death", and advises having someone spot you, never standing on the top rung, and keeping the ladder away from power lines.
Pitch, degrees and roof area
The slope factor is how much longer the sloped roof is than its flat footprint: multiply the footprint area by it to get roof area for shingles. It is √(1 + (pitch ÷ 12)²).
| Pitch | Degrees | Slope factor | Roof area over 1,000 sq ft of footprint |
|---|---|---|---|
| 1/12 | 4.8° | 1.003 | 1,003 sq ft |
| 2/12 | 9.5° | 1.014 | 1,014 sq ft |
| 3/12 | 14.0° | 1.031 | 1,031 sq ft |
| 4/12 | 18.4° | 1.054 | 1,054 sq ft |
| 5/12 | 22.6° | 1.083 | 1,083 sq ft |
| 6/12 | 26.6° | 1.118 | 1,118 sq ft |
| 7/12 | 30.3° | 1.158 | 1,158 sq ft |
| 8/12 | 33.7° | 1.202 | 1,202 sq ft |
| 9/12 | 36.9° | 1.250 | 1,250 sq ft |
| 10/12 | 39.8° | 1.302 | 1,302 sq ft |
| 12/12 | 45.0° | 1.414 | 1,414 sq ft |
The roofing calculator applies the factor for you and counts bundles, and the rafter calculator uses the same pitch to size rafter length.
Which materials the code allows at your pitch
The 2021 International Residential Code sets a minimum slope for each roof covering. Local codes can differ, so check with your building department.
| Roof covering | Minimum pitch | IRC section |
|---|---|---|
| Standing-seam metal panels | ¼/12 | R905.10.2 |
| Lapped metal panels | 3/12 (½/12 with lap sealant) | R905.10.2 |
| Mineral-surfaced roll roofing | 1/12 | R905.5.2 |
| Asphalt shingles | 2/12 (double underlayment from 2/12 up to 4/12) | R905.2.2 |
| Clay and concrete tile | 2½/12 (double underlayment from 2½/12 to 4/12) | R905.3.2 |
| Metal roof shingles | 3/12 | R905.4.2 |
| Wood shingles and wood shakes | 3/12 | R905.7.2, R905.8.2 |
| Slate | 4/12 | R905.6.2 |
For workplace safety rules, OSHA calls a roof of 4/12 or less "low-slope" and anything steeper a "steep roof". Those rules cover employers, not homeowners, and a fall from a low-slope roof can still kill.
Frequently asked questions
What is a 4/12 roof pitch in degrees?
About 18.4 degrees. A 6/12 roof is about 26.6 degrees and a 12/12 roof is 45 degrees.
How do I convert degrees to roof pitch?
Multiply 12 by the tangent of the angle. For example, 30° gives 12 × tan(30°) ≈ 6.9, a pitch of about 7/12.
What is the minimum pitch for asphalt shingles?
The 2021 IRC (R905.2.2) allows asphalt shingles on slopes of 2/12 or more, with double underlayment required from 2/12 up to 4/12.
Can I measure roof pitch from the ground?
Not with a tape. InterNACHI notes some phone apps estimate slope from a photo taken from the ground. For a direct reading, use the attic method or a level held against a rake board.
Calculators for this
Roofing Shingle
Estimate roof area from your house footprint and pitch, then get squares, shingle bundles, nails, underlayment, drip edge and cost.
Rafter Length & Roof Pitch
Get common rafter length from building width and roof pitch, with overhang, roof angle, plumb and seat cuts and a to-scale drawing.
Attic Ventilation
How much attic ventilation do you need?
Published 2026-11-10. Sources: 2021 International Residential Code, chapter 9 Roof Assemblies (Colorado adoption, via UpCodes); InterNACHI, Roof Slope and Pitch; Apple, iPhone User Guide: Use iPhone as a level; OSHA, 29 CFR 1926.500 Definitions; U.S. Consumer Product Safety Commission, Home Safe: Outdoor Repairs checklist. See how we calculate.