Quick answer: roof pitch = rise ÷ run × 12, written as “x/12”. A roof that rises 6 inches over 12 inches of run is a 6/12 pitch, which is 26.6°. To get degrees from a pitch, take the arctangent of rise ÷ run.
What roof pitch means
Roof pitch tells you how steep a roof is. In the US it is written as two numbers, such as 4/12 or 8/12. The first number is the rise, how many inches the roof climbs, and the second is the run, always 12 inches of level distance. So a 4/12 roof climbs 4 inches for every foot you move toward the ridge.
The same steepness can be described three ways, and different people use different ones. Roofers and lumber yards talk in x/12. Engineers, architects and phone apps often use the roof angle in degrees. Building codes and some product sheets use percent grade. The calculator shows all three, so you can talk to everyone in their own language.
How to measure roof pitch
You don’t need to climb onto the roof. These methods go from most accurate to quickest:
From the attic or under the eave (most accurate)
- Find a rafter, or the underside of the roof overhang outside.
- Hold a level against the bottom edge so it is perfectly horizontal, with one end touching the rafter.
- Mark the level at 12 inches from that end.
- Measure straight up (or down) from the 12-inch mark to the rafter. That number is your pitch. If it measures 7 inches, you have a 7/12 roof.
From the gable end
Measure the height from the top of the wall to the peak (the rise) and half the width of the building (the run). Type both into “Rise & run” in any unit. A rise of 8 ft over a run of 16 ft is a 6/12 pitch.
From the ground
Stand square to a gable, line up an angle app or a photo with the roof edge, and read the angle. Enter it under “Angle”. This is good enough to tell a 4/12 from an 8/12, but not for cutting rafters.
How to calculate roof pitch
Whatever units you measure in, the pitch is simply the ratio of rise to run, scaled to 12:
Pitch = rise ÷ run × 12 · Angle = arctan(rise ÷ run)
Your gable rises 5 ft 3 in over a run of 14 ft.
5.25 ÷ 14 × 12 = 4.5/12. The angle is arctan(5.25 ÷ 14) = 20.6°.
Most roofers would call this a 4½/12 roof. The calculator rounds to the nearest standard pitch for you.
Going the other way, from degrees to pitch, multiply the tangent of the angle by 12. A 30° roof is tan(30°) × 12 = 6.93, close to a 7/12 pitch.
Roof pitch chart: degrees, slope factor and roof area
This chart lets you convert roof pitch to degrees at a glance and gives every multiplier you need for estimating. “Rafter per ft of run” is how long the rafter is for each foot it covers on the level. “Roof per 1,000 sq ft” shows how much roof surface sits on a 1,000 sq ft footprint, so you can see how quickly material adds up on steeper roofs.
| Pitch | Angle | Grade | Slope factor | Rafter per ft of run | Hip / valley factor | Roof per 1,000 sq ft |
|---|---|---|---|---|---|---|
| 1/12 | 4.76° | 8.3% | 1.003 | 12.04 in | 1.417 | 1,003 sq ft |
| 2/12 | 9.46° | 16.7% | 1.014 | 12.17 in | 1.424 | 1,014 sq ft |
| 3/12 | 14.04° | 25.0% | 1.031 | 12.37 in | 1.436 | 1,031 sq ft |
| 4/12 | 18.43° | 33.3% | 1.054 | 12.65 in | 1.453 | 1,054 sq ft |
| 5/12 | 22.62° | 41.7% | 1.083 | 13.00 in | 1.474 | 1,083 sq ft |
| 6/12 | 26.57° | 50.0% | 1.118 | 13.42 in | 1.500 | 1,118 sq ft |
| 7/12 | 30.26° | 58.3% | 1.158 | 13.89 in | 1.530 | 1,158 sq ft |
| 8/12 | 33.69° | 66.7% | 1.202 | 14.42 in | 1.563 | 1,202 sq ft |
| 9/12 | 36.87° | 75.0% | 1.250 | 15.00 in | 1.601 | 1,250 sq ft |
| 10/12 | 39.81° | 83.3% | 1.302 | 15.62 in | 1.641 | 1,302 sq ft |
| 11/12 | 42.51° | 91.7% | 1.357 | 16.28 in | 1.685 | 1,357 sq ft |
| 12/12 | 45.00° | 100.0% | 1.414 | 16.97 in | 1.732 | 1,414 sq ft |
| 14/12 | 49.40° | 116.7% | 1.537 | 18.44 in | 1.833 | 1,537 sq ft |
| 16/12 | 53.13° | 133.3% | 1.667 | 20.00 in | 1.944 | 1,667 sq ft |
| 18/12 | 56.31° | 150.0% | 1.803 | 21.63 in | 2.062 | 1,803 sq ft |
| 20/12 | 59.04° | 166.7% | 1.944 | 23.32 in | 2.186 | 1,944 sq ft |
| 24/12 | 63.43° | 200.0% | 2.236 | 26.83 in | 2.449 | 2,236 sq ft |
Degrees to roof pitch chart
Plans from Europe and Canada, angle finders and phone apps give the angle in degrees. Use this table to convert degrees to pitch; the “nearest” column rounds to the half-inch steps roofers and truss plants use.
| Angle | Exact pitch | Nearest pitch | Grade |
|---|---|---|---|
| 5° | 1.05/12 | 1/12 | 8.7% |
| 10° | 2.12/12 | 2/12 | 17.6% |
| 15° | 3.22/12 | 3/12 | 26.8% |
| 20° | 4.37/12 | 4.5/12 | 36.4% |
| 25° | 5.60/12 | 5.5/12 | 46.6% |
| 30° | 6.93/12 | 7/12 | 57.7% |
| 35° | 8.40/12 | 8.5/12 | 70.0% |
| 40° | 10.07/12 | 10/12 | 83.9% |
| 45° | 12.00/12 | 12/12 | 100.0% |
| 50° | 14.30/12 | 14.5/12 | 119.2% |
| 55° | 17.14/12 | 17/12 | 142.8% |
| 60° | 20.78/12 | 21/12 | 173.2% |
Worked examples for every method
There is more than one way to find a roof’s pitch. Here is each method with real numbers, so you can check your own result by hand.
1. With a level and tape
You hold a 12 in level against a rafter and measure 7 in from the 12 in mark to the rafter. The pitch is simply 7/12, which is arctan(7 ÷ 12) = 30.26°.
2. From rise and run at the gable
The peak is 8 ft above the top of the wall and the building is 32 ft wide, so the run is 16 ft. 8 ÷ 16 × 12 = 6/12, or 26.57°.
3. From an angle
An angle finder reads 22.5°. tan(22.5°) × 12 = 4.97, so the roof is a 5/12 pitch.
4. From a rafter you can measure
A rafter covers a run of 12 ft and is 13 ft 5 in (13.417 ft) long along its edge. The rise is √(13.417² − 12²) = 6.0 ft, so the pitch is 6 ÷ 12 × 12 = 6/12. Choose “Rafter” in the calculator to do this in one step.
5. From a percent grade
A product sheet says the minimum slope is 25%. 25 × 12 ÷ 100 = 3/12.
Common roof pitches and where you see them
Most roofs fall into a few familiar groups. Knowing them helps you sanity-check a measurement: if your number lands far outside the usual range for your style of house, measure again.
- Flat and low slope, ¼/12 to 2/12. Commercial buildings, modern additions, porches tied in under a second-story window. These need membrane or standing-seam roofing, not ordinary shingles.
- Low, 3/12 to 4/12. Ranch homes, garages, carports and sheds. Shingles work from 4/12 with normal underlayment and from 2/12 with double underlayment.
- Conventional, 5/12 to 9/12. The great majority of American houses. 6/12 is a builder favorite because it sheds water well, gives a usable attic and is still walkable.
- Steep, 10/12 to 12/12. Colonial, Cape Cod and Craftsman gables, cottages in snowy regions. The attic can often become living space.
- Very steep, over 12/12. Tudor and Gothic Revival gables, A-frames, church steeples. Expensive to roof and almost always needs staging or harnesses.
Converting between pitch, degrees and percent
Because all three describe the same triangle, you can go from any one to the others with a calculator or by hand:
- Pitch to degrees: angle = arctan(pitch ÷ 12). For 8/12: arctan(0.667) = 33.7°.
- Degrees to pitch: pitch = tan(angle) × 12. For 40°: tan(40°) × 12 = 10.07, so about 10/12.
- Pitch to percent: percent = pitch ÷ 12 × 100. For 3/12: 25%.
- Percent to pitch: pitch = percent × 12 ÷ 100. A 50% slope is 6/12.
Metric plans in Europe and Canada often give roof slope in degrees only. To order US materials for a 35° roof, convert first: tan(35°) × 12 = 8.4, so an 8½/12 pitch. Some older plans write pitch as a fraction of the span instead, such as “⅓ pitch”; that means the rise is one third of the span, which is an 8/12 roof.
How pitch affects attic space, snow and style
If you are designing an addition or a new garage, pitch is a choice and not just a measurement. A steeper roof gives a taller attic, which can become storage or a bonus room, and sheds snow and leaves faster. It also costs more: more roof surface for the same footprint, longer rafters or bigger trusses, and slower, more careful installation.
A lower roof is cheaper and easier to build, sits lower against the sky and suits modern and ranch styles, but holds snow longer and limits your roofing choices. Matching the pitch of the main house usually looks best on an addition. When you can’t, for example under a second-floor window, a lower pitch with metal roofing is a common fix.
From pitch to roof area and squares
A sloped roof covers more surface than the flat area of the house beneath it. The steeper the roof, the bigger the difference. That is what the slope factor is for: multiply your floor plan area (including the overhangs) by it to get the true roof area.
Roofing is sold by the square, which is 100 sq ft of roof. A house with a 1,500 sq ft footprint and a 6/12 roof has 1,500 × 1.118 = 1,677 sq ft of roof, or 16.8 squares. Shingle bundles usually come three to a square, and most roofers add 10–15% for waste on a simple gable roof, more on roofs with many hips and valleys. Type your footprint into the optional field and the calculator does all of this for you.
Roof pitch by roofing type
Pitch decides which roofing you can use, because water has to run off before it can find a way in. These are the minimum slopes in the International Residential Code (IRC); manufacturers often ask for more, and your local code has the final word.
| Roofing | Minimum slope (IRC) | Notes |
|---|---|---|
| Asphalt shingles | 2/12 | 2/12 to under 4/12 needs double underlayment |
| Metal panels, lapped seams | 3/12 | Without seam sealant |
| Standing-seam metal | ¼/12 | Seamed panels made for low slopes |
| Clay or concrete tile | 2½/12 | Below 4/12 needs extra underlayment |
| Wood shingles / shakes | 3/12 · 4/12 | Shingles 3/12, shakes 4/12 |
| Membrane (EPDM, TPO) | ¼/12 | “Flat” roofs still need a little fall |
Steepness, walkability and cost
Up to about 6/12, most roofers can walk a dry roof normally. From around 7/12 to 8/12, footing gets tricky and roof jacks or harnesses come out. Above 9/12, roofers treat it as a steep-slope job, which takes longer and often costs more per square. Never walk a wet, icy or mossy roof at any pitch, and use fall protection whenever you are near the edge.
Notes for engineers, estimators and contractors
Slope factor. For pitch p (rise per 12 run), the common-rafter factor is √(1 + (p/12)²). Multiply horizontal run or plan area by it to get length or surface along the slope.
Hip and valley factor. For equal pitches on both sides, a hip runs √2 × the common run horizontally, so its factor per unit of common run is √(p² + 288) ÷ 12. At 6/12 that is exactly 1.5.
Precision. A 1/8-inch error on a 12-inch level reading moves the pitch by 0.125/12, about 0.3°. Measure over a longer run (say 24 or 48 in) and enter both numbers for a better figure.
Code references. Minimum slopes above follow IRC Chapter 9 (R905). Always confirm with the manufacturer’s installation instructions and the edition adopted locally.
Tips
- Measure two rafters. Older houses sag; if two readings differ, use the average.
- Include the overhangs in the footprint when you work out the roof area.
- Going on to framing? Use the pitch you found here in the rafter length and roof truss calculators.
- Send it to your roofer. Use WhatsApp or Email under the result to share the pitch and area.
Frequently asked questions
What is a 6/12 roof pitch in degrees?
A 6/12 pitch is 26.57 degrees. The roof rises 6 inches for every 12 inches of horizontal run, which is also a 50% grade.
What is a 4/12 pitch in degrees?
A 4/12 pitch is 18.43 degrees, a fairly low but very common slope for ranch houses, porches and garages.
Is a 12/12 pitch 45 degrees?
Yes. A 12/12 roof rises 12 inches for every 12 inches of run, which is exactly 45 degrees and a 100% grade.
How do I measure roof pitch from the ground?
Stand back from a gable end and hold your phone with a level or angle app lined up with the roof edge, or take a straight-on photo and measure the angle. Then convert the angle to pitch with this calculator. For an exact figure, measure a rafter from the attic.
What is the minimum pitch for asphalt shingles?
The International Residential Code allows asphalt shingles on slopes of 2/12 or steeper, but slopes from 2/12 up to 4/12 need a double layer of underlayment. Check your shingle maker’s instructions and local code.
What is the most common roof pitch?
Most American houses fall between 4/12 and 9/12. Within that range, 6/12 is a popular balance between drainage, attic space and how easy the roof is to work on.
What pitch is a 30 degree roof?
A 30° roof is a 6.93/12 pitch, so roofers would call it a 7/12. The grade is 57.7%.
Is a 3/12 roof too flat for shingles?
No, but it is close to the limit. The IRC allows asphalt shingles down to 2/12, and anything below 4/12 needs two layers of underlayment. Many roofers prefer metal or a membrane below 3/12.
What roof pitch is walkable?
Most roofers can walk a dry roof up to about 6/12 without special gear. From around 7/12 to 8/12 footing gets difficult, and above that roof jacks, toe boards or a harness are normally used. Never walk a wet, icy or mossy roof.
What is a roof pitch multiplier?
It is the slope factor: the number you multiply a flat (plan) measurement by to get the length or area along the roof. For 6/12 it is 1.118, for 12/12 it is 1.414. The chart on this page lists it for every common pitch.
What is the best roof pitch for snow?
There is no single code minimum for snow; the roof structure is designed for your local snow load. Steeper roofs, roughly 6/12 and up, shed snow more easily, and metal roofing sheds it fastest. Ask a local builder or engineer about the design snow load for your area.
What is the difference between pitch and slope?
People use them interchangeably. Strictly, pitch is rise over the full span, while slope is rise over run, which is what the x/12 figure describes. Roofers today almost always mean rise over 12 inches of run.
How much bigger is the roof than the floor plan?
Multiply the footprint by the slope factor. At 6/12 the factor is 1.118, so a 1,500 sq ft footprint has about 1,677 sq ft of roof surface, or 16.8 squares, before waste.