8/12 Roof Pitch: Degrees, Multiplier and What It Means
An 8/12 roof rises 8 inches for every 12 inches of run. That is 33.69°, a pitch multiplier of 1.202 and a slope of 66.7%. Here is what those numbers do to your roof area, your materials and your quote.
8/12 at a glance
Colonials, Cape Cods, storey-and-a-half houses and steep gable fronts.
Nearby pitches
8 in rise per 12 in run
atan(8 ÷ 12) = 33.69°
√(8² + 12²) ÷ 12 = 1.202
8 ÷ 12 × 100 = 66.7%
Measured something different? The roof pitch calculator takes any rise and run, or an angle, and gives you all four numbers with the full reference chart.
Turn this pitch into a roof size
Measure the roof surface at this pitch, then price the whole job.
What an 8/12 roof pitch means
An 8/12 roof rises 8 inches for every 12 inches of run. It is a steep roof: past the point where a roofer can simply walk it, and past the point where published cost tables stop describing your house. You see it on Colonials, Cape Cods and any design that needs usable headroom in the top storey.
8/12 in degrees
The angle is the arctangent of rise over run:
atan(8 ÷ 12) = atan(0.6667) = 33.69°
That is the angle between the roof surface and horizontal. It is the number a smartphone level app gives you if you hold it flat against the slope, and the number to enter if a supplier asks for degrees rather than a ratio.
The 8/12 pitch multiplier
The pitch multiplier turns the flat footprint of a roof into its real sloped area. It is the hypotenuse of the rise-and-run triangle divided by the run:
√(8² + 12²) ÷ 12 = √208 ÷ 12 = 1.202
So a 2,000 square foot footprint on an 8/12 roof is about 2,405 square feet of actual roof surface, or 24.1 roofing squares before any waste allowance. Use the roof area calculator to do this for a footprint that is not a simple rectangle, and the roofing square calculator to add a waste factor and convert to squares and bundles.
How 8/12 compares with the 6:12 that cost tables assume
Published roofing cost tables are built on a 6:12 roof. The HomeGuide roof replacement cost guide states in the footnote to its cost-by-house-size table that the figures are based on a single-storey home with a 6:12 roof pitch. An 8/12 roof has 7.5% more surface than that, on the same footprint — so a table priced off your house size understates the material your roof actually needs.
| Footprint | Roof at 8:12 | Roof at 6:12 | Difference |
|---|---|---|---|
| 1,200 | 1,440 sq ft | 1,340 sq ft | +7.5% |
| 1,600 | 1,925 sq ft | 1,790 sq ft | +7.5% |
| 2,000 | 2,405 sq ft | 2,235 sq ft | +7.6% |
| 2,400 | 2,885 sq ft | 2,685 sq ft | +7.4% |
Areas are rounded to the nearest 5 square feet. These are surface-area differences only. We do not publish a percentage for the labour surcharge on steep roofs, because none of the sources this site cites puts a number on it.
Walking on an 8/12 roof
An 8/12 roof is past the comfortable range. The HomeGuide cost guide puts roofs with pitches over 6:12 in the group that needs extra safety precautions and more labour, and 8/12 is squarely in it. Expect roof jacks, planking or a harness on any quote.
Slope is not a constraint at 8/12
Nothing is ruled out by slope at 8/12 — it is far above every code minimum. The constraint runs the other way: some heavy materials get harder and slower to set on a steep slope, and a few interlocking tile systems need extra fasteners or battens above a certain pitch. That is a manufacturer instruction, not a code limit.
For what the finished roof costs once you know your square count, see the roof replacement cost guide, or price a specific material with the roof replacement cost calculator.
Sources
- 2024 International Residential Code, Chapter 9 — minimum slopes for asphalt shingles and the underlayment requirement below 4:12 (R905.2.2).
- HomeGuide roof replacement cost guide — the cost-by-house-size table and its 6:12 footnote, and the note that slopes over 6:12 need extra safety precautions and more labour.
- Angle, multiplier and slope percentage are computed from the pitch, not taken from a source. The arithmetic is shown above so you can check it.
Every source on this site is listed on the methodology page. Nobody involved in this site installs roofs.
Related calculators and guides
8/12 roof pitch FAQ
Can you walk on an 8/12 roof?
Not safely without equipment. The HomeGuide cost guide groups roofs steeper than 6:12 as needing extra safety precautions and more labour. At 33.69 degrees an 8/12 roof normally needs roof jacks and planking or a fall-arrest harness.
What is an 8/12 pitch in degrees?
33.69 degrees. The arithmetic is atan(8 divided by 12), which is atan(0.6667).
Does an 8/12 roof cost more to replace?
Yes, for two separate reasons. It has about 7.5 percent more surface area than the 6:12 roof that cost tables assume, so it needs more material; and HomeGuide lists slopes over 6:12 as requiring extra safety precautions and more labour. We do not publish a percentage for that labour surcharge because no source we cite quantifies one.
How much bigger is an 8/12 roof than a 6/12 roof?
About 7.5 percent, on the same footprint. A 2,000 square foot footprint gives roughly 2,405 square feet at 8/12 against 2,235 at 6/12.