How to measure it without getting on the roof
You need a level, a tape measure and a place to stand inside. The attic method is the one to use, because it is the one that does not involve a ladder.
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Get into the attic and find a rafter you can reach. Any rafter on the main roof will do, as long as it runs from the wall up to the ridge rather than framing a dormer.
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Hold the level horizontally with one end touching the underside of the rafter. Get the bubble centered. That end is your starting point.
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Measure 12 inches along the level from the rafter and mark it. If your level is shorter than 12 inches, use whatever length it is and put that number in the run field above.
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Measure straight up from the mark to the underside of the rafter. That distance is your rise.
Six inches means a 6 in 12 roof. Nine inches means 9 in 12. Fractions are normal and the calculator takes them, so a rise of seven and a half inches is a 7.5 in 12 pitch.
Two ways to get it wrong
Do not rest the level on the shingles. Shingle courses step, so a gauge laid straight on them bridges the steps and reads low. Roofers who have compared the two report an error of roughly 2 in 12, which is enough on its own to move a roof across the threshold where shingles stop being permitted. Measure against a rafter, or against something flat spanning several courses.
Take the reading in more than one place. A settled house does not have one pitch, it has a pitch per rafter, and the differences are largest on the oldest roofs. Three readings that agree are worth more than one that is convenient.
Do not let anyone round it
If your roof measures 3.5 in 12, it is 3.5 in 12. It is not 4 in 12, and the difference is not pedantry.
Four in 12 is a code threshold. Below it, asphalt shingles are still permitted but the code requires a second layer of underlayment beneath them, and shingle manufacturers draw the same line in their own installation instructions. Those instructions are what the warranty is written against, so a roof rounded up from 3.5 to 4 gets one layer where it needed two, on precisely the shallow roofs most likely to leak, and the homeowner loses the warranty they paid for at the same time.
Homeowners who measure carefully and then read the code report being told by every bidder to round up anyway. It saves the crew a layer. It costs the reader the warranty. This is why the field above accepts quarter inches and why the readout prints what you measured rather than the nearest whole number.
The manufacturer's own line, for one common shingle: GAF Timberline application instructions, which require two layers of deck protection from 2:12 to less than 4:12 and one layer at 4:12 or more
If the attic is not reachable
Some houses have no attic access, and on a cathedral ceiling there is nothing to measure against. There are two workarounds, and both are worse than the attic method, so treat what they give you as approximate.
From a ladder at the gable end, hold the level against the rake board, the trim that runs up the sloping edge of the roof, and take the same measurement. You are on a ladder against a wall rather than on the roof itself, which is the safer of the two positions, but it is still a ladder.
Reading the pitch off a photograph is the method to avoid. In principle the ratio survives the scaling, so measuring rise and run on the image should work. In practice a phone held at any angle other than dead level changes the apparent slope, and the error is invisible in the photograph. Asked to estimate the pitch from the same two images, a room full of carpenters returned answers from 2 in 12 to 3.5 in 12. That spread is wide enough to cross two separate code thresholds, so a photograph is worth using to decide whether a roof is shallow or steep and worth nothing at all for deciding what may be laid on it.
Every pitch, converted
The whole range a house roof is likely to sit in. The multiplier column is the one that costs money, because it is what turns the ground your house covers into roof you have to pay to cover.
| Pitch | Angle | Slope | Fraction | Multiplier | Roof vs footprint |
|---|---|---|---|---|---|
| 1 in 12 | 4.8° | 8.3% | 1/24 | 1.003 | 0.3% more |
| 2 in 12 | 9.5° | 16.7% | 1/12 | 1.014 | 1.4% more |
| 3 in 12 | 14.0° | 25.0% | 1/8 | 1.031 | 3.1% more |
| 4 in 12 | 18.4° | 33.3% | 1/6 | 1.054 | 5.4% more |
| 5 in 12 | 22.6° | 41.7% | 5/24 | 1.083 | 8.3% more |
| 6 in 12 | 26.6° | 50.0% | 1/4 | 1.118 | 11.8% more |
| 7 in 12 | 30.3° | 58.3% | 7/24 | 1.158 | 15.8% more |
| 8 in 12 | 33.7° | 66.7% | 1/3 | 1.202 | 20.2% more |
| 9 in 12 | 36.9° | 75.0% | 3/8 | 1.250 | 25.0% more |
| 10 in 12 | 39.8° | 83.3% | 5/12 | 1.302 | 30.2% more |
| 11 in 12 | 42.5° | 91.7% | 11/24 | 1.357 | 35.7% more |
| 12 in 12 | 45.0° | 100.0% | 1/2 | 1.414 | 41.4% more |
Where each column comes from
Take the rise, divide it by 12, and you have the slope as a decimal. A 6 in 12 roof gives 0.5.
The slope percentage is that decimal as a percentage, so 6 in 12 is a 50% slope. This is the form used on drawings outside the United States and in civil engineering, and it is worth knowing because a 100% slope is 45 degrees rather than vertical, which surprises people.
The angle is the arctangent of that decimal. For 6 in 12 that is 26.6 degrees. Nobody in the trade quotes a roof in degrees, but drawing software and pitch-finder apps report them, so the conversion has to be here.
Degrees are where the intuition breaks, and it catches tradespeople as often as homeowners. A 6 in 12 roof is not half of a 12 in 12 roof measured in degrees: it is 26.6 rather than 22.5. The relationship is a tangent, not a straight line, and the quickest way to feel it is to notice that doubling a 12 in 12 roof to 24 in 12 gives 63.4 degrees rather than 90. Nothing you can build reaches 90, because a vertical wall has no run to divide by.
The fraction is the rise divided by the span, and the span is twice the run. A 6 in 12 roof is a quarter pitch, because 6 over 24 reduces to 1 over 4. This is the older convention and the reason the words pitch and slope pull apart, which the next section deals with.
The multiplier is the square root of one plus the square of the slope decimal. For 6 in 12 that is the square root of 1.25, or 1.118. It is the same number for two different jobs: multiply a horizontal run by it to get a rafter length, or multiply a footprint by it to get roof area.
Carpenters have called it the bridge measure for as long as there have been framing squares, and it is printed on the face of any square carrying a rafter table, stated as inches of rafter per foot of run. Those tables give 13.42 for a 6 in 12 and 13.89 for a 7 in 12. Divide either by twelve and you have the multiplier in the readout above, 1.118 and 1.158. The column is a hundred years older than this page.
Pitch, slope, and why one roof has two numbers
Strictly, they are different measurements. Slope is rise over run, written as a rise in 12, which is what a roofer says out loud and what this page puts in the big readout. Pitch is rise over span, written as a fraction, and the span is the whole width the roof crosses rather than half of it.
So a roof that a roofer calls 6 in 12, a framing table calls a quarter pitch. Both describe the same roof. The fraction is always half what you might expect, because the span is always twice the run.
In everyday American use the distinction has mostly collapsed and pitch now means slope, which is why this page is called a pitch calculator and prints a rise in 12. The fraction still turns up in older framing references and on architectural drawings, so it is in the readout rather than left out.
What your pitch decides
This is the part the other pitch calculators leave out. The number is not trivia. It settles what can go on the roof, who can walk on it, and what the job costs.
What you are allowed to put on it
The building code sets a minimum slope for every roof covering, and below that minimum the covering is not permitted. This is the part of a pitch that homeowners find out about late, usually when a contractor turns down a job on a porch or an extension.
The reason is water. On a shallow roof, wind drives rain uphill under the laps between shingles faster than gravity pulls it off, and the covering stops being a covering. A membrane has no laps to drive water under, which is why the flattest roofs use one.
| Covering | Minimum slope | Code section |
|---|---|---|
| Built-up, single-ply and modified bitumen membranes | 1/4 in 12 | R905.9.1, R905.11 to R905.13 |
| Standing seam metal panels | 1/4 in 12 | R905.10.2 |
| Lapped metal panels, with lap sealant | 1/2 in 12 | R905.10.2 |
| Mineral-surfaced roll roofing | 1 in 12 | R905.5.2 |
| Asphalt shingles | 2 in 12 | R905.2.2 |
| Photovoltaic shingles | 2 in 12 | R905.16.2 |
| Clay and concrete tile | 2.5 in 12 | R905.3.2 |
| Metal shingles | 3 in 12 | R905.4.2 |
| Wood shingles and shakes | 3 in 12 | R905.7.2, R905.8.2 |
| Lapped metal panels, no lap sealant | 3 in 12 | R905.10.2 |
| Slate | 4 in 12 | R905.6.2 |
2021 International Residential Code, chapter 9 · the same chapter as adopted and published free by Seattle
The publisher of the code puts its own text behind a sign-in. Every figure in the table was read from a city's published adoption of it, which reproduces the section word for word and is a PDF anyone can open.
Three things in that table are worth reading twice.
Metal is not one answer. A standing seam panel goes down to a quarter in 12. The same metal in lapped panels with no sealant at the laps needs 3 in 12, twelve times the slope. So the answer to whether metal will work on a shallow roof depends entirely on which metal, and a flat quote for metal roofing does not tell you.
Asphalt shingles stop at 2 in 12, and get a condition at 4. Between 2 in 12 and 4 in 12 the code requires a double layer of underlayment beneath them. That is real work and real material that a shallow roof needs and a steeper one does not, and it belongs on the quote.
Slate needs the most slope of anything. At 4 in 12 it is out of reach for a great many American houses, which is part of why it stays a regional covering.
Two cautions, and the first one matters more than the table.
A code minimum is a floor, not a recommendation. The roofing industry's own association recommends 4 in 12 or more for asphalt shingle, clay and concrete tile, metal shingle, slate and wood shake and shingle roofs, which is two whole units above the code floor for asphalt. A manufacturer is free to require more slope than the code as well, and their instructions, not the code, are what a warranty claim is judged against. Legal, recommended and warranted are three different lines, and only the first is in the table.
Your state adopts its own edition. Amendments happen, so the section numbers above are where to look rather than the final word.
One more thing worth knowing if you go and read the code yourself. Beside each threshold it prints a percentage, and for clay and concrete tile that percentage is wrong. The code calls 2.5 in 12 a 25 percent slope. It is 20.8 percent, and the commercial code, published by the same body for the same slope, prints 21 percent. The ratio is the number that governs and the percentage beside it is a convenience, but here the convenience is mistaken. The equivalent parentheticals for asphalt shingles and for the 4 in 12 line are both correct, so this is a slip rather than a rounding convention.
Three different lines, and none of them is the same line
Pitch has more than one threshold, and they are set by different people for different reasons. That is why the answers you get sound like they contradict each other.
- 3 in 12 divides the roofing industry's own product categories. Above it is steep-slope roofing, at or below it is low-slope roofing, and they are different products.
- 4 in 12 is the safety line. OSHA calls anything steeper a steep roof, and it is also where the code stops asking for a second layer of underlayment under shingles.
- 7 in 12 is the money line. It has no basis in safety law or in the building code. It is where estimating software starts adding a surcharge, because it is where a crew stops working normally.
A roof at 5 in 12 is a steep-slope product, a steep roof to OSHA, and an ordinary roof to the person pricing it. All three are true at once.
NRCA, Professional Roofing, "Slope matters"
The valley is not the roof
A roof with two planes meeting at a right angle has a valley running between them, and that valley is always shallower than either plane. Its rise is the same, but it travels a diagonal, so its run is longer by the square root of two.
The number that falls out is uncomfortable. Two planes at 4 in 12, legal for asphalt shingles and comfortably above the code floor, meet in a valley running at 2.83 in 12. That is below the minimum for wood shingles and shakes, for metal shingles and for lapped metal panels. A roof can be legal on every plane and out of spec in the line where the water actually concentrates.
The trade association raises this and the code does not, which is a fair summary of the difference between the two. The readout above prints the valley for whatever pitch you enter, and flags it when it drops under the 3 in 12 floor that the planes themselves clear.
NRCA, Professional Roofing, "Slope matters"
What it costs
Two ways, and they are separate.
First, the multiplier. A steeper roof is a bigger roof over the same house, and you pay per square of roof surface, not per square foot of ground. Going from 4 in 12 to 9 in 12 on the same footprint adds 18.6% to the surface you are buying, which on a $12,000 job is around $2,200 before anything else changes.
Second, the steep slope charge. From 7 in 12 a roof stops being walkable for production work and estimators add a line for it. Read from two real insurance estimates, that line runs +14.6 to 18.8% on the install from 7 in 12 to 9 in 12, and +22.9 to 29.5% from 10 in 12 to 12 in 12.
Those two stack. A 10 in 12 roof carries 16.5% more surface than a 6 in 12 roof on the same house, and then the surcharge lands on top of the larger figure.
On the larger of the two estimates, a real 51.93 square job, the steep lines came to $2,164.04 against a line item total of $21,317.55. Pitch alone was 10.2% of that roof.
Workflow Solutions (Xactimate estimate) · Your Virtual Adjuster (Xactimate estimate) · Roofing Contractor
Both estimates are from 2021, and both bill the charge a second time against the tear-off, which we could not verify as a rate and so did not put in the arithmetic. Read the percentages as a floor. The full working, and what happens to it in the price, is on the roof cost calculator.
Where else pitch shows up on a bill
Insurance estimates are one publisher, so we looked for the same effect somewhere unrelated. Craftsman Book Company's estimating manual prices several trades by pitch, and its break falls in the same place.
Cedar roofing shingles carry a line reading "add for pitch over 6 in 12" at 40% of labor. Roof sheathing is priced at 1.72 crew hours per square up to 6 in 12 and 2.00 from 7 in 12 to 9 in 12, which is 16.3% more labor for the same square of roof.
Two publishers, two trades, one threshold. Note what is being priced, though: labor hours on a specific covering, not a surcharge on a whole asphalt job. It corroborates that the step is real and where it sits, not the size of the step on your roof.
Craftsman Book Company, 2016 National Construction Estimator, roofing and log home sections
Who can walk on it
Roofers will tell you a 6 in 12 is walkable, an 8 in 12 wants care and anything past 10 in 12 needs equipment. That is a comfort scale for people who do it daily, and it sits a long way above the regulatory line.
OSHA defines a steep roof as anything greater than 4 in 12, and the definition has teeth. On a low-slope roof a crew may work behind a warning line with a safety monitor. On a steep roof they must have guardrails with toeboards, safety nets, or a personal fall arrest system, once they are six feet up. So the roof a contractor calls easy is the same roof their own crew is required to be tied off on.
The reason is in the fatality figures. Roofers died at 48.7 per 100,000 full-time equivalent workers in 2024, against 3.3 for American workers as a whole, which is about fifteen times the rate, and the third highest of any occupation for which the Bureau of Labor Statistics published a rate that year. Only logging and fishing were worse.
None of that governs you on your own house. OSHA writes duties for employers, not for homeowners, and no one is going to cite you for climbing your own ladder. It is offered as calibration: the people who are best at this, with the most practice and the right equipment, are required to be tied off on a roof they would describe as easy. The attic method at the top of this page costs nothing and asks you to climb nothing.
29 CFR 1926.500, definitions · 29 CFR 1926.501(b)(10) and (b)(11) · BLS, Census of Fatal Occupational Injuries 2024
Questions people ask about pitch
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What is the most common roof pitch?
Between 4 in 12 and 9 in 12 covers most American houses, and this is stated everywhere without a source behind it. We looked for published data on the distribution of residential roof pitches and did not find any, so treat that range as trade folklore rather than a measurement.
What is documented is the effect of the choice. Each step up the table costs you roof surface, and from 7 in 12 it costs you a surcharge as well.
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Can I put metal on a low slope roof?
It depends which metal, and the gap is enormous. A standing seam system is permitted down to a quarter in 12. The same metal in lapped panels with no sealant at the laps needs 3 in 12, which is twelve times the slope. With sealant applied at the laps it sits between the two at a half in 12.
So "can I use metal" has no answer and "can I use this metal" has three. Anyone quoting a single minimum pitch for metal roofing is wrong for two of the three cases, and it is the most common metal question homeowners ask.
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My roof already has shingles and I have just measured it under 2 in 12. What now?
What changes is not how long the shingles last, it is that the roof has been exposed to leaks from the day it was laid, because wind drives water back under laps that were never designed for that angle.
What matters next is what went down underneath. A roof laid with the double underlayment the code asks for between 2 and 4 in 12, or with a full ice and water membrane, has a second line of defense even where the shingles are out of spec. One laid with a single layer of felt does not. That is worth establishing before deciding whether to act, and it is a question a roofer can answer from the tear-off records or from a small inspection.
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Can I get my pitch from a photo of the house?
Not reliably enough to act on. Camera tilt changes the apparent slope and leaves no trace in the image, so the error is invisible. Asked to read the same two photographs, experienced carpenters returned answers spanning 2 in 12 to 3.5 in 12.
That spread crosses the line where shingles become permitted and lands either side of the line where they need a second layer of underlayment. A photo is good for telling shallow from steep. It is not good for anything that follows from the number.
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Does a steeper roof last longer?
Water leaves it faster, which helps, and it holds less snow. Against that, a steep roof takes more sun on the upper faces and every repair on it costs more, because the same surcharge that applies to a replacement applies to a patch.
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My roof has two different pitches. Which one do I use?
Measure each one and work them out separately, then add the areas. A main roof at 8 in 12 with a porch at 3 in 12 is two roofs for pricing, and often two different coverings, because the porch may be below the minimum slope for what is on the main house.
If you only want a rough total, use the pitch of the largest section. The error is the difference between the two multipliers applied to the smaller area, which on a typical porch is a few percent of the job.
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Why does the calculator round the multiplier to three decimals?
Because every figure on this site has to be reproducible on a pocket calculator from the other figures on the page. If we printed 1.118 and priced at 1.1180339887, the working line would not add up when you checked it.
The cost of that discipline is at most a fifth of an inch on a 40 foot rafter run, and about 9 square feet on a 20,000 square foot footprint. Neither changes a decision.