How to measure roof pitch
Measure roof pitch by holding a level flat and measuring straight down (or up) to the roof 12 in along it. That vertical distance in inches is the pitch. Four ways to get it:
- On the roof or a ladder: set one end of a 2 ft level on the shingles, level it, and measure from the 12 in mark down to the roof surface.
- In the attic: hold the level against the underside of a rafter and measure from the 12 in mark up to the rafter edge.
- With a speed square: hold the square's pivot point on the rafter or roof edge, rotate it until the body is plumb, and read the pitch where the edge crosses the common scale.
- From the gable end: measure the total rise from the top plate to the ridge and half the building width, then enter both. Any units work because pitch is a ratio.
A phone inclinometer gives degrees directly; type that into the angle field to convert it to a pitch.
Roof pitch chart: pitch to degrees
Each pitch converts to one roof pitch angle, one percent slope and one rafter factor; the factor turns a level run into the rafter length.
| Pitch | Degrees | Percent | Rafter factor | Hip/valley factor |
|---|---|---|---|---|
| 1/12 | 4.76° | 8.3% | 1.003 | 1.417 |
| 2/12 | 9.46° | 16.7% | 1.014 | 1.424 |
| 3/12 | 14.04° | 25% | 1.031 | 1.436 |
| 4/12 | 18.43° | 33.3% | 1.054 | 1.453 |
| 5/12 | 22.62° | 41.7% | 1.083 | 1.474 |
| 6/12 | 26.57° | 50% | 1.118 | 1.5 |
| 7/12 | 30.26° | 58.3% | 1.158 | 1.53 |
| 8/12 | 33.69° | 66.7% | 1.202 | 1.563 |
| 9/12 | 36.87° | 75% | 1.25 | 1.601 |
| 10/12 | 39.81° | 83.3% | 1.302 | 1.641 |
| 11/12 | 42.51° | 91.7% | 1.357 | 1.685 |
| 12/12 | 45° | 100% | 1.414 | 1.732 |
| 14/12 | 49.4° | 116.7% | 1.537 | 1.833 |
| 16/12 | 53.13° | 133.3% | 1.667 | 1.944 |
| 18/12 | 56.31° | 150% | 1.803 | 2.062 |
The hip/valley factor is the hip length per unit of common run on a roof where both planes share the pitch; the hip roof calculator uses it.
Minimum roof pitch for each roofing material
The roofing decides the lowest pitch you can build, and steep barn roofs like the gambrel roof calculator draws sit at the other end of the chart: asphalt shingles need 2/12, and between 2/12 and 4/12 they need two layers of underlayment[1]. The calculator's check lists all of these:
| Roof covering | Minimum pitch | Section |
|---|---|---|
| Asphalt shingles | 2/12 (9.5°) | R905.2.2; 2/12 to 4/12 needs double underlayment |
| Clay or concrete tile | 2.5/12 (11.8°) | R905.3.2; under 4/12 needs double underlayment |
| Metal roof shingles | 3/12 (14°) | R905.4.2 |
| Wood shingles or shakes | 3/12 (14°) | R905.7.2, R905.8.2 |
| Slate | 4/12 (18.4°) | R905.6.2 |
| Mineral-surfaced roll roofing | 1/12 (4.8°) | R905.5.2 |
| Standing-seam metal panels | 0.25/12 (1.2°) | R905.10.2 |
| Lapped metal panels, no sealant | 3/12 (14°) | R905.10.2 |
| Lapped metal panels with sealant | 0.5/12 (2.4°) | R905.10.2 |
| Built-up, modified bitumen, single-ply | 0.25/12 (1.2°) | R905.9.1, R905.11.1, R905.12.1 |
Below 3/12, the IRC also wants ridges, hips and valleys designed as beams rather than framed with a plain ridge board[2]. For a lean-to or shed roof that ends up near these limits, try the shed roof pitch calculator; for metal panels, the metal roof calculator.
Pitch, slope and angle in metric countries
The UK and Australia usually quote roof pitch in degrees, and the US in inches per foot. A 30° roof is 6.93/12; a 45° roof is 12/12. The tool also gives the rise per metre (a 6/12 roof rises 500 mm per metre). Stair pitch uses the same idea with a different limit: England caps a private stair at 42°[3].
From pitch to rafters
Multiply the level run by the rafter factor for the rafter's line length: half of a 24 ft building is 12 ft of run, and 12 × 1.118 = 13′ 5″ at 6/12. The rafter calculator adds the overhang, ridge deduction and birdsmouth, and the roof calculator turns the same factor into roof area.
Common roof pitch mistakes
Pitch errors usually come from measuring along the roof or mixing up units:
- Measuring along the slope. Pitch uses level run; 12 in along the shingles is less than 12 in of run.
- Using the full span as the run. On a gable, the run of each rafter is half the building width.
- Reading pitch as degrees. A 6/12 roof is 26.57°, not 6°.
- Old "fraction" pitch. Some older plans give pitch as rise over the full span: a "1/4 pitch" roof rises 1/4 of the span, which is 6/12.
- Ignoring the roofing minimum. Asphalt shingles need at least 2/12 under the 2021 IRC (R905.2.2)[1].
Parts of a roof
Pitch, rise and run describe the triangle every common rafter sits on; the run is half the span and the overhang is measured level. The diagram labels each part:
Frequently asked questions
How do I convert roof pitch to degrees?
Take the arctangent of pitch ÷ 12. A 6/12 roof is arctan(0.5) = 26.57°, an 8/12 roof is 33.69° and a 12/12 roof is 45°.
What is the roof pitch angle of a 4/12 roof?
18.43°. The angle is the arctangent of rise ÷ run: 4 ÷ 12 = 0.333, and arctan(0.333) = 18.43°.
What is a 6/12 roof pitch in degrees?
26.57°. A 4/12 roof is 18.43° and an 8/12 roof is 33.69°.
How do I calculate roof pitch?
Divide the rise by the run and multiply by 12. A roof that rises 5 ft over 15 ft of run is 5 ÷ 15 × 12 = 4/12.
What is the minimum roof pitch for shingles?
2/12 under IRC R905.2.2, with double underlayment from 2/12 up to 4/12.
Is there a roof pitch calculator app?
Yes: this page is built to work as one on a phone. It runs in any mobile browser with no sign-up, and you can add it to your home screen from the browser menu.
Is roof pitch the same as roof slope?
In everyday use, yes: both mean rise over run. Some texts reserve "pitch" for rise over the full span, but builders and this calculator use rise per 12 in of run.
What is the standard roof pitch?
There is no single standard. The code sets a minimum for each roofing material (2/12 for asphalt shingles, 3/12 for wood shingles, 4/12 for slate), and the design picks anything above that.
Can you shingle a 3/12 roof?
Yes. Asphalt shingles are allowed down to 2/12, but from 2/12 to 4/12 the IRC requires two layers of underlayment (R905.2.2).
What is a roof pitch multiplier?
The rafter factor √(1 + (pitch ÷ 12)²): multiply the flat area or the level run by it to get roof area or rafter length. For 6/12 it is 1.118.
Is there a minimum roof pitch for snow?
The IRC sets no minimum pitch for snow. Snow load is handled by rafter size: the IRC rafter tables are grouped by ground snow load (30, 50 and 70 psf).
Is a roof slope calculator the same as a pitch calculator?
Yes. Slope is the same rise-over-run ratio, often given as a percent: 6/12 is a 50% slope, 26.57°.