What angle is a 6/12 roof pitch?

26.57 degrees. The conversion is the arctangent of the ratio: atan(6 ÷ 12) = atan(0.5). Common references: 4/12 is 18.43°, 8/12 is 33.69°, and 12/12 is exactly 45°.

What is the difference between pitch and slope percent?

Both describe steepness, scaled differently. Pitch states rise per 12 units of run (6/12). Slope percent states rise per 100 units (the same roof is 50%). A 100% slope is 45° — a 12/12 roof — not a vertical wall.

What is the roof slope multiplier used for?

It converts flat measurements into sloped ones. Multiply a house footprint by the multiplier to get true roof area for shingles, or multiply a horizontal run by it to get rafter length. At 6/12 the multiplier is 1.118, so a 1,200 sq ft footprint carries 1,342 sq ft of roof.

How do I measure my roof pitch without climbing on it?

In the attic: hold a level horizontally against the underside of a rafter, mark 12 in along it from the rafter face, then measure straight up from that mark to the rafter — that vertical is your rise over 12. A pitch-finder app on a phone held to a gable-end bargeboard also works well.

What is the minimum pitch for shingles?

Standard asphalt shingles are rated for 4/12 and steeper. Between 2/12 and 4/12 they require enhanced underlayment systems, and below 2/12 you need a low-slope membrane or metal system instead. Always confirm against the specific product's installation spec.

Roof Pitch Calculator — Free, With Formula & Worked Example

About this calculator

Pitch is expressed as rise over a 12 in run (6/12), but material specs also use degrees and percent slope. This converter moves between all three and returns the slope multiplier used by every roofing and rafter calculation.

What this number means

Roof slope is one number wearing three costumes. Carpenters and shingle specs speak in pitch — inches of rise per 12 inches of run (6/12). Engineers and metal-roofing specs speak in degrees. Drainage, ramps and some material warranties speak in percent slope. They are all the same slope, and confusing them is expensive: a "6 percent" roof and a "6/12" roof differ by a factor of eight.

The fourth number, the multiplier, is the one that turns flat measurements into real roof area: multiply a footprint (or a horizontal run) by it and you get the sloped surface or the rafter length. It is the engine inside the Roofing Calculator.

The formula

Everything follows from the slope ratio r = rise ÷ run:

Pitch = r × 12, expressed as x/12
Angle = atan(r), in degrees
Slope percent = r × 100
Slope multiplier = √(1 + r²)
Rafter length per 12 in of horizontal run = 12 × multiplier, in inches

Worked example

The classic 6/12 roof. Rise 6 in over a 12 in run, so r = 0.5.

Angle = atan(0.5) = 26.57°
Slope = 0.5 × 100 = 50%
Multiplier = √(1.25) = 1.118 — every horizontal foot is 1.118 ft of roof
Rafter length = 12 × 1.118 = 13.42 in of rafter per foot of run

Reference points: 4/12 = 18.43° = 33.3% slope, multiplier 1.054 · 9/12 = 36.87° = 75%, multiplier 1.250 · 12/12 = 45° = 100%, multiplier 1.414.

Assumptions and limitations

Pitch here is the simple slope ratio. (Traditional carpentry also uses "pitch" for rise ÷ span, a different fraction — in modern US roofing specs, x/12 means rise over run, which is what this calculator uses.)
The multiplier converts horizontal measurements to slope measurements for a single uniform plane. Gambrel, mansard and curved roofs have no single multiplier.
Minimum slopes matter for materials: standard shingles generally need 4/12 or steeper (2/12–4/12 requires double underlayment or special systems), and standing-seam metal can go lower. Check the product spec in degrees or x/12 — not percent.