Roof pitch reference
6/12 Roof Pitch
A 6/12 roof pitch rises 6 inches for every 12 inches of horizontal run. That is 26.57 degrees from level, an exact 50 percent grade, and a slope factor of 1.1180, so every square foot of floor area underneath carries 1.1180 square feet of roof above it.
It is the most common pitch on American houses, and the one people most often get wrong when converting to degrees.
| Rise over run | 6 in 12 |
|---|---|
| Angle | 26.57° |
| Grade | 50.0% |
| Slope factor (multiplier) | 1.1180 |
| Rafter per foot of run | 13.42 in |
| Roof area on a 1,700 sq ft footprint | 1,901 sq ft (19.0 squares) |
A 6/12 is not 22.5 degrees, and here is why
This trips up more people than any other pitch question, and the reasoning behind the mistake is perfectly sensible. A 12/12 roof is 45 degrees. A 6/12 is half the rise of a 12/12. So a 6/12 should be half of 45, which is 22.5 degrees. It is not. It is 26.57 degrees, a full 4 degrees steeper than the intuition says.
The reason is that pitch converts to angle through the tangent, and tangent is not a straight line. The angle is the arctangent of rise divided by 12, and arctangent climbs quickly at the shallow end then flattens out as it approaches 90 degrees. Halving the rise does not halve the angle anywhere on that curve.
If you want the pitch that genuinely is 22.5 degrees, it is 4.97/12, which rounds to a 5/12. So the roof people picture when they say "half of a 12/12" is actually closer to a 5/12 than a 6/12.
The practical consequence is small but real: if you are reading an angle off a phone inclinometer and converting it in your head, the error compounds in the direction of under-ordering material. Use the pitch calculator and let the arctangent do its own work.
Why 6/12 became the default American pitch
Ask a builder to draw a house and the roof will very likely come out at 6/12. It is the single most common residential pitch in the United States, and that is not an accident of taste. It is the point where four separate constraints happen to agree.
It sheds water and snow briskly, so debris does not sit and the details stay dry. It takes every roofing material without qualification, since it is well clear of the minimum slope for asphalt, tile, shake and metal alike. It is still comfortably walkable, so a crew works on it without staging. And it produces usable attic volume underneath, which a 4/12 largely does not.
Go shallower and you gain nothing but a slightly smaller roof. Go steeper and you start paying for labor access before you gain much drainage benefit. The roof types guide covers how the shape interacts with this, because a 6/12 gable and a 6/12 hip do not cost the same even at identical pitch.
What a 6/12 pitch does to the cost
A 6/12 roof covering a 1,700 square foot footprint is 1,901 square feet of actual roof surface, or 19 roofing squares. The 201 square feet above the footprint is slope, and it is material and labor you pay for whether or not anyone thinks about it.
The table prices the same house at every common pitch from this site's own data, tear-off of one layer included, everything else held constant.
Two comparisons are worth reading off it. Dropping from 6/12 to 4/12 saves about 109 square feet and roughly $353 at the low end, which is real but modest, and you give up attic headroom for it. Going up to 8/12 adds about 142 square feet and roughly $931, and that figure understates the jump because 8/12 is where crews start adding roof jacks and a steep-slope charge the table does not model. The honest read is that 6/12 sits just below the point where pitch starts costing more than area alone explains.
| Pitch | Roof area | Estimated cost |
|---|---|---|
| 2/12 | 1,723 sq ft | $7,645 to $11,521 |
| 3/12 | 1,752 sq ft | $7,763 to $11,712 |
| 4/12 | 1,792 sq ft | $8,144 to $12,295 |
| 5/12 | 1,842 sq ft | $8,292 to $12,502 |
| 6/12this page | 1,901 sq ft | $8,497 to $12,795 |
| 8/12 | 2,043 sq ft | $9,427 to $14,153 |
| 12/12 | 2,404 sq ft | $10,911 to $16,326 |
The last comfortably walkable pitch
A roofer will walk a 6/12 in proper footwear, standing upright, carrying bundles, without roof jacks or staging. That is the top of the range where that is true. At 7/12 footing starts to go, by 8/12 most crews are setting toe boards, and above 9/12 the job needs staging and fall arrest as a matter of routine.
Walkable does not mean unprotected. Under OSHA's definitions a 6/12 is already a steep roof, since the line sits at anything over 4 in 12, so a crew working on one 6 feet or more above the ground must use guardrails with toeboards, safety nets or personal fall arrest (29 CFR 1926.501(b)(11)). What walkability buys is pace: the crew stands upright and carries bundles across the roof instead of working from jacks and planks.
This matters when reading an estimate. The step from 6/12 to 8/12 does not just add roof area, it changes how the crew works and how long they take. Many contractors start a steep-slope charge around 8/12, and published figures for it vary so widely, from a small add-on per square to a large premium on the labor, that the only reliable number is the one on your own quote. Ask for it as its own line.
It is also why 6/12 shows up so often in tract and spec housing. It is the steepest pitch that still prices like an easy roof.
How to check whether your roof is actually 6/12
Work from inside if you can. Hold a 12 inch level horizontally against the underside of a rafter in the attic, level it, then measure straight down from the free end to the rafter. Six inches means 6/12. The attic is safer than the roof and the rafter gives a cleaner reading than shingles do.
From outside, lay a 2 foot level on the roof surface, level it, mark 12 inches from the contact point and measure down. Same arithmetic. Do not do this on a wet roof.
If all you have is an angle, remember the lesson above and convert properly: rise equals the tangent of the angle times 12. A reading of 26.5 to 26.6 degrees is a 6/12. Anything near 22.5 is a 5/12, not a 6/12.
Put this to work