Question 1

How do I measure roof pitch?

Accepted Answer

Hold a level horizontally against the roof, mark 12 inches along it, and measure straight down from that mark to the roof surface. That vertical distance in inches is the rise per 12 inches of run — a 6-inch drop is a 6/12 pitch.

Question 2

What does 6/12 pitch mean?

Accepted Answer

The roof rises 6 inches for every 12 inches of horizontal run. That works out to 26.57 degrees and a pitch factor of 1.118, meaning the actual roof surface is about 12% larger than the footprint beneath it.

Question 3

What is a pitch factor and why do I need it?

Accepted Answer

It is the multiplier that converts flat footprint area into actual sloped roof area. A 1,500 ft² footprint at 6/12 pitch has about 1,677 ft² of roof surface. Ordering shingles off the footprint alone leaves you short.

Question 4

How do I convert roof pitch to degrees?

Accepted Answer

Take the arctangent of rise divided by run. A 4/12 pitch is arctan(4/12) = 18.4 degrees; 12/12 is exactly 45 degrees.

Question 5

What roof pitch is walkable?

Accepted Answer

Up to about 7/12 most roofers walk unaided in good conditions. From 8/12 to 9/12 roof jacks or a harness become normal, and above that staging and fall protection are required.

Question 6

What is the minimum pitch for asphalt shingles?

Accepted Answer

IRC R905.2.2 sets 2/12 as the absolute minimum, and between 2/12 and 4/12 a doubled underlayment is required. Below 2/12 you need a membrane roof rather than shingles.

Question 7

What is the difference between pitch and slope?

Accepted Answer

Pitch is traditionally the ratio of rise to the full span; slope is rise over run, expressed per 12. In everyday roofing conversation the two are used interchangeably to mean rise-over-12, which is what this calculator reports.

Question 8

How does pitch affect the cost of a roof?

Accepted Answer

Steeper roofs cost more twice over: there is more surface area for the same footprint, and labour rates rise once the roof stops being walkable. Above 8/12 many roofers add a steep-slope charge of 20% or more.

Roof Pitch Calculator

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