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How to find roof pitch: three ways to measure it safely

Roof pitch tells you how steep a roof is, and you need it to order shingles, plan gutters or check whether a roofing material is allowed. You rarely need to climb onto the roof to find it. This guide shows three safer methods and how to convert pitch to degrees and a pitch factor.

Updated By Matholio Editorial Team3 min read

The short answer

Roof pitch is the rise in inches for every 12 inches of horizontal run, written as rise/12. Hold a level horizontal against a rafter in the attic, mark 12 inches along it and measure straight up to the rafter: if that is 6 inches, the roof is a 6/12 pitch, which is about 26.6 degrees with a pitch factor of 1.118.

What roof pitch means

In the US, pitch is written as a ratio of rise to a run of 12 inches. A 4/12 roof rises 4 inches for every foot it runs horizontally; a 12/12 roof rises a foot for every foot, which is 45 degrees. Roofers also talk about slope as a percentage and about the pitch factor, the number you multiply a flat footprint by to get the real sloped roof area.

Pitch = rise ÷ run × 12, written as rise/12

Angle = arctan(rise ÷ run)

Pitch factor = √(rise² + run²) ÷ run

Method 1: from the attic

This is the safest and most accurate method, and the one This Old House recommends.

  1. Take a level of at least 12 inches and a tape measure into the attic.
  2. Hold one end of the level against the underside of a rafter and keep it perfectly horizontal.
  3. Mark the level at 12 inches from the point where it touches the rafter.
  4. Measure straight up from the 12 inch mark to the underside of the rafter.
  5. That measurement in inches is the rise. A 6 inch rise means a 6/12 pitch.

Method 2: from a ladder at the eaves

With no attic access, set a ladder securely at the edge of the roof and work from the ladder, not the roof. Rest one end of a level on the shingles with the level pointing down the slope, hold it level, and measure straight down from the 12 inch mark to the roof surface. That distance is the rise. Only do this on a dry day with someone holding the ladder.

A phone angle app or a digital angle finder laid on the shingles gives the angle in degrees directly; use the table below to convert it to a pitch.

Method 3: from the ground at the gable end

On a simple gable roof, the triangle on the end wall gives you the pitch. Measure the width of the house at the gable and halve it to get the run. Estimate the height of the triangle, from the top of the wall to the ridge, by counting siding courses or measuring from an upstairs window. Then divide.

  1. House width at the gable: 26 ft, so the run is 13 ft, or 156 in.
  2. Height from the top of the wall to the ridge: 6 ft 6 in, or 78 in.
  3. Pitch: 78 ÷ 156 × 12 = 6, so the roof is a 6/12 pitch.

Enter the rise and run in inches into the roof pitch calculator and it works out the pitch, angle and pitch factor for you. This method is an estimate; confirm it from the attic if you are ordering materials.

Roof pitch to degrees, slope and pitch factor

Common roof pitches converted
Pitch Angle Slope Pitch factor
2/12 9.46° 16.7% 1.014
3/12 14.04° 25% 1.031
4/12 18.43° 33.3% 1.054
5/12 22.62° 41.7% 1.083
6/12 26.57° 50% 1.118
7/12 30.26° 58.3% 1.158
8/12 33.69° 66.7% 1.202
9/12 36.87° 75% 1.25
10/12 39.81° 83.3% 1.302
12/12 45° 100% 1.414

Multiply the footprint of the roof, including overhangs, by the pitch factor to get the roof area. A 40 × 30 ft footprint at 6/12 is 1,200 × 1.118 = 1,342 sq ft of roof.

Why pitch matters

  • Material: the International Residential Code (R905.2.2) allows asphalt shingles only on slopes of 2/12 or steeper, and requires double underlayment from 2/12 up to 4/12. Flatter roofs need membrane roofing.
  • Quantity: steeper roofs have more surface for the same footprint, so they need more shingles and underlayment.
  • Safety: roofs steeper than about 6/12 are hard to walk on, and most roofers use extra fall protection on them.
  • Drainage: low-slope roofs shed water slowly and need closer attention to flashing and gutters.

Calculators for this job

These calculators do the arithmetic from this guide. Each card shows the result for a typical project; open one to enter your own measurements.

Roof Pitch Calculator 6 in rise over 12 in 6/12 Open calculator Roofing Calculator 40 × 30 ft roof at 6/12 14.76 squares Open calculator

Frequently asked questions

What is the most common roof pitch?

Many US houses have pitches between 4/12 and 9/12. A 6/12 pitch, about 26.6 degrees, is very common for asphalt shingle roofs.

How do I convert roof pitch to degrees?

Take the arctangent of rise ÷ 12. For a 6/12 roof, arctan(0.5) is about 26.6 degrees. The table above lists the common pitches.

Can I find the pitch from the ground?

Yes, roughly. On a gable end, divide the height of the triangle by half the house width and multiply by 12. Confirm from the attic before you order materials.

What is the minimum pitch for asphalt shingles?

The IRC allows asphalt shingles on slopes of 2/12 or more, with double underlayment between 2/12 and 4/12. Check the shingle maker’s instructions too, since some products require more.

Sources

  1. This Old House, How to Determine Roof Pitch
  2. International Code Council, 2021 International Residential Code, Chapter 9: Roof Assemblies
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