Roof Pitch Calculator - Degrees, Slope and Multiplier

Pitch	Angle	Slope	Area ×
4/12	18.4°	33.3%	1.054
5/12	22.6°	41.7%	1.083
6/12	26.6°	50.0%	1.118
7/12	30.3°	58.3%	1.158
8/12	33.7°	66.7%	1.202
9/12	36.9°	75.0%	1.250
10/12	39.8°	83.3%	1.302
12/12	45.0°	100.0%	1.414

Pitch	rise in inches per 12 in of run
Angle	atan(rise ÷ 12) in degrees
Slope percent	rise ÷ 12 × 100
Area multiplier	√(rise² + 144) ÷ 12

What is Roof Pitch Calculator?

Roof pitch describes how steeply a roof rises. In the United States it is written as the rise in inches over a fixed 12 in of horizontal run, so a 6/12 roof climbs 6 in for every foot it travels inward. Pitch converts cleanly into three other numbers: the angle in degrees from horizontal, the slope as a percentage, and the area multiplier that tells you how much more surface a sloped roof has than the flat footprint beneath it. The multiplier is the square root of the rise squared plus 144, divided by 12. Multiply your footprint by it and you get the roof area you actually shingle, which is what every material order depends on.

Common uses for Roof Pitch Calculator

Read a 6/12 pitch off a set of plans and convert it to degrees
Check whether a roof is walkable before you plan the work
Turn a building footprint into real roof area for a material order
Compare two roof designs by slope and surface area
Confirm the minimum pitch a shingle product allows before you order

Pitch, slope and angle are three views of one number

Pitch is the ratio written over 12. Slope is the same ratio as a percentage, so 6/12 is 50 percent. Angle is the arctangent of the rise divided by 12, so 6/12 is 26.6 degrees. Plans use pitch, code tables mix pitch and slope, and a level or framing square reads pitch directly on the roof. Once you have the rise over any measured run, the calculator converts between all three.

The multiplier is the number you actually need

Shingles, underlayment and ventilation are ordered by roof surface, not by floor area. The multiplier bridges the two: square the rise, add 144 for the 12 in run, take the square root and divide by 12. A 4/12 roof adds about 5 percent area, a 6/12 about 12 percent, an 8/12 about 20 percent and a 12/12 about 41 percent. Steeper roofs also take more fasteners and more labor.

Reading pitch on an existing roof

Hold a level horizontally with one end on the roof surface, mark 12 in along it, then measure straight down from that mark to the roof. The vertical distance in inches is your rise over 12. Do it in two or three places, because older roofs sag and re-roofs add layers. From the ground, measure the rise and run at a gable end and divide.

Frequently Asked Questions

What does a 6/12 pitch mean?

It means the roof rises 6 in for every 12 in of horizontal run, so it gains half a foot of height for every foot it travels inward. That equals about 26.6 degrees and a 50 percent slope. Pitch is always written as rise over 12, so 4/12, 6/12, 8/12 and 12/12 are the common values.

How do I find the area multiplier?

Divide the rise by 12, square the result, add one, then take the square root. For a 6/12 pitch: 0.5 squared is 0.25, plus one is 1.25, and the square root of that is 1.118. Multiply the footprint by 1.118 and 1,200 sq ft becomes about 1,342 sq ft of roof.

What is the minimum pitch for asphalt shingles?

The IRC allows asphalt shingles down to a 2/12 slope when a double layer of underlayment is installed, with stricter underlayment rules between 2/12 and 4/12, and a different roof covering below 2/12. Manufacturers set their own minimums too, so check the product data sheet and confirm with your local building department.

Which roof pitches can you walk on?

Roofers generally treat 6/12 and below as walkable with care, 7/12 to 9/12 as needing roof jacks or a harness, and anything steeper as specialist work. The practical limit depends on the surface as much as the angle. Never work on a wet or frosty roof at any pitch.