Roof Pitch Chart
Roof pitch is written as rise in 12. A 6:12 roof rises 6 inches for every 12 inches of horizontal run. The chart below converts the common pitches into degrees, a percentage, and the two multipliers you need for working out roof area.
The chart
| Pitch | Degrees | Percent | Slope factor | Hip & valley factor |
|---|---|---|---|---|
| 1:12 | 4.76° | 8.3% | 1.0035 | 1.4167 |
| 2:12 | 9.46° | 16.7% | 1.0138 | 1.4240 |
| 3:12 | 14.04° | 25.0% | 1.0308 | 1.4361 |
| 4:12 | 18.43° | 33.3% | 1.0541 | 1.4530 |
| 5:12 | 22.62° | 41.7% | 1.0833 | 1.4743 |
| 6:12 | 26.57° | 50.0% | 1.1180 | 1.5000 |
| 7:12 | 30.26° | 58.3% | 1.1577 | 1.5298 |
| 8:12 | 33.69° | 66.7% | 1.2019 | 1.5635 |
| 9:12 | 36.87° | 75.0% | 1.2500 | 1.6008 |
| 10:12 | 39.81° | 83.3% | 1.3017 | 1.6415 |
| 11:12 | 42.51° | 91.7% | 1.3566 | 1.6853 |
| 12:12 | 45.00° | 100.0% | 1.4142 | 1.7321 |
Reading a row is straightforward. Take 8:12: the roof climbs 8 inches for each foot of run, that works out at 33.69 degrees, and it is a 66.7 percent grade. The last two columns are multipliers, and they are what the chart is really for on site.
Two notes on the numbers. The percent column is the rise divided by the run, so 6:12 is 50 percent rather than 50 degrees. And percent and degrees only agree at zero, so a 100 percent roof is 45 degrees, not vertical. The values here were worked out from the pitch rather than copied from another chart, using degrees = arctan(rise ÷ 12).
Turning a roof plan into roof area
This is the part a lot of charts leave out, and it is the reason a roofer keeps one in the van. A roof covers more surface than the ground it sits over, because the slope stretches it. The slope factor is how much more.
roof area = roof plan area × slope factor
Measure the plan eave to eave, not wall to wall. The overhang is roof, and it is the mistake that shortens an order. The formula also assumes every plane on the roof carries the same pitch; a roof with planes at different pitches has to be worked out plane by plane.
Say the roof plan measures 42 ft by 32 ft eave to eave, giving 1,344 square feet, and the pitch is 6:12. The slope factor is 1.1180, so the roof surface is 1,344 × 1.1180 = 1,503 square feet. That is before waste, openings and whatever allowance the job calls for.
The hip and valley factor is a different job. It does not touch area. It converts a horizontal distance into the length of a hip or valley rafter running diagonally across two slopes, which is why every value in that column is larger. On a 6:12 roof the factor is exactly 1.5, so a hip covering 10 feet of plan run measures 15 feet along the timber.
It only holds for the ordinary case: two planes of equal pitch meeting at a right angle in plan. Unequal pitches, or a corner that is not square, need compound roof geometry worked out for that specific intersection. Cutting from this column on a skewed or unequal-pitch hip will give you the wrong rafter.
Both multipliers come from the same idea as the rafter in the drawing above: a sloping line is longer than its shadow on the ground. If you want the numbers for one specific roof rather than a chart row, the roof pitch calculator takes the rise and run directly.
Pitch or slope, and why the trade argues about it
Nearly everyone says “pitch” and means the rise-in-12 number in the chart above. That is how the trade talks, and you will usually be understood on a roofing or framing site. Strictly, though, the two words once meant different things, and the older meaning still turns up.
| Slope | Pitch, strictly | |
|---|---|---|
| Measured against | The run, 12 inches | The span, the full width |
| Written as | 6:12, or 6 in 12 | 1/4 |
| Same roof | 6:12 | 1/4 pitch |
A 6:12 roof on a 24 foot span rises 12 feet over 24, which is a quarter, so the old books call it a quarter pitch. InterNACHI, the home inspectors’ association, keeps the distinction and says the two terms being used interchangeably is incorrect.
Even the professionals are split. On InterNACHI’s own forum, inspectors argue both ways. Some say to drop “slope” because everyone on site says pitch and using the other word makes you sound like you have never been on a roof. Others point at the code: an InterNACHI educator notes there that the 2018 IRC uses “slope” 170 times against 10 for “pitch”, and that the 2021 edition simply defines pitch as “see slope”. Builders on the Fine Homebuilding forum reach the same shrug, that carpenters use the two interchangeably whatever the textbook says.
There is one place the difference has teeth. A framing square is marked in slope, not pitch. Wikipedia’s article on roof pitch makes the point directly: the tables and markings on a framing square represent slope, because they assume a 12 inch run. So if a drawing calls for a quarter pitch and you set the square to 4 and 12 because a quarter looked like a third of twelve, you are cutting the wrong roof. Read a fraction as the old pitch and a ratio as slope, and the ambiguity is gone.
The practical advice is short: say the two numbers. “Six in twelve” cannot be misread by anyone, whichever word they use for it.
2021 IRC minimum slopes for selected roof coverings
Pitch is not only a shape, it decides what you are allowed to put on the roof. Water moves slowly on a shallow roof and gets more chance to work back under a lap, so the code sets a floor for each covering. The figures below are from the 2021 IRC and cover common coverings rather than every roof system on the market.
| Covering | Minimum slope | IRC section |
|---|---|---|
| Asphalt shingles | 2:12, with double underlayment below 4:12 | R905.2.2 |
| Clay and concrete tile | 2.5:12, with double underlayment below 4:12 | R905.3.2 |
| Metal roof shingles | 3:12 | R905.4.2 |
| Wood shingles | 3:12 | R905.7.2 |
| Wood shakes | 3:12 | R905.8.2 |
| Slate | 4:12 | R905.6.2 |
| Metal panels, lapped, no sealant | 3:12 | R905.10.2 |
| Metal panels, lapped, with sealant | 0.5:12 | R905.10.2 |
| Standing seam metal | 0.25:12 | R905.10.2 |
| Built-up roof | 0.25:12 | R905.9.1 |
Two things to take from that table. Shingles stop at 2:12, which is why a 1:12 porch roof gets standing seam or a membrane instead. And between 2:12 and 4:12 shingles are allowed but only with underlayment doubled, which is the step people skip.
Local amendments exist and your inspector has the final word, so treat this as the shape of the rule rather than the last word on your job.
Measuring the pitch you have
You do not need to be on the roof, and for anything steep you should not be. The safest version is done in the loft against a rafter.
- Hold a spirit level against the underside of a rafter and bring it level.
- Measure 12 inches along the level from the point where it touches the rafter, and mark it.
- Measure straight up from that mark to the rafter. That distance in inches is your rise in 12.
If it comes out at 5 and a half rather than a whole number, the roof is not necessarily odd. Old rafters move, and measuring across two or three of them and taking the common answer is more reliable than trusting one. For a slope stated in a survey or on a drawing instead of measured by hand, the driveway slope calculator handles the same rise-and-run arithmetic for ground work, where the numbers usually arrive as a percentage.
Frequently asked questions
What roof pitch is walkable?
There is no universally safe walkable pitch. No number makes a roof safe to stand on, and pitch is only one of the things that decides it.
As a rule of thumb from the trade, roofers often treat anything up to about 6:12 as manageable in ordinary boots and 7:12 upwards as calling for staging, harnesses or roof jacks. That is custom, not a safety standard, and no code sets it.
Surface, weather and experience matter more than the ratio. Wet, mossy, frosted or dusty covering turns a comfortable 4:12 into something nobody should be standing on, worn shingles are slicker than new ones, and the height of the fall decides what a slip costs. Fall protection is a separate question from pitch and is worth answering first.
Can you put asphalt shingles on a 3:12 roof?
Yes, with a condition. The IRC allows asphalt shingles down to 2:12, so 3:12 is inside the range, but anything below 4:12 calls for a double layer of underlayment (section R905.2.2).
Below 2:12 shingles are out and you are into standing seam metal or a membrane. Check the shingle manufacturer’s own instructions too, since a warranty can ask for more than the code does.
What roof pitch is 30 degrees?
About 7:12. Thirty degrees works out at a rise of 6.93 inches in 12, so 7:12 at 30.26 degrees is the nearest standard pitch and is close enough for most purposes.
Going the other way, the pitch that lands on a round 30 degrees exactly is not a whole number of inches, which is why charts stop at 7:12 and 30.26.
What is a roof pitch multiplier?
Another name for the slope factor in the chart. Multiply the horizontal area of the roof plan by it and you get the actual area of the roof surface, which is what you order materials against.
On a 6:12 roof the multiplier is 1.1180, so a 1,344 square foot roof plan carries 1,503 square feet of surface. Measure the plan eave to eave rather than wall to wall, and remember the steeper the roof, the bigger the gap between the two figures.
Is roof pitch the same as roof slope?
In everyday use, yes. Almost everyone says pitch and means the rise-in-12 figure, and you will usually be understood.
Strictly they differ. Slope compares the rise to a 12 inch run and gives 6:12. Pitch compares the rise to the whole span and gives a fraction, so the same roof is a quarter pitch. It matters when you meet a fraction on an old drawing, because a framing square is marked in slope.
What is the standard roof pitch for a house?
Most ordinary houses sit somewhere between 4:12 and 9:12. That range sheds water well, takes standard shingles without extra underlayment, and stays buildable without special access.
Climate and structural design both push it around. Steeper roofs are common in snow country, though the design question is snow load and where the snow ends up rather than simply shedding it, since a roof that dumps its load over a doorway creates a different problem. Flatter roofs are more common where the weather is dry.
What is a 4:12 pitch in degrees and percent?
18.43 degrees, and 33.3 percent.
Those two numbers describe the same roof in different units, and the gap between them catches people out. Percent is the rise divided by the run, so a 4:12 roof is a third of the way up. Degrees is the angle the rafter makes with the horizontal.
What is the lowest pitch a roof can be?
Down to a quarter inch in 12 for a standing seam metal roof or a built-up membrane, which is the shallowest the IRC allows for a drained roof.
A roof described as flat is not truly flat. It still needs that quarter inch per foot so water leaves rather than sitting, and ponding is what shortens a low roof’s life.