Calculators / Water and gutters

Roof pitch calculator

Put in the rise and run, or the angle, for the pitch, the degrees and the roof surface. Or type your address and we’ll read the pitch of each face of your roof from the USGS laser survey.

Updated November 2026 · How we check our numbers

Your roof pitch

6/12 pitch

26.6° from flat. Your 1,800 sq ft footprint is 2,012 sq ft of roof: 20.1 squares before waste.

Pitch: 6/12
Angle: 26.6°
Slope: 50%
Pitch factor: 1.118
Roof surface: 2,012 sq ft
Squares: 20.1

Estimate for planning only, not professional advice. Check the manufacturer’s instructions, your local code and a licensed professional before you buy, build or install. Use at your own risk. Terms.

Size the guttersThe gutter calculator scales roof area by pitch (SMACNA's factor); this fills in 6/12.

rise per foot = 6 ÷ 12 × 12 = 6.00 in

angle = atan(6.00 ÷ 12) = 26.6°

pitch factor = √(1 + (6.00 ÷ 12)²) = 1.118

surface = 1,800 sq ft × 1.118 = 2,012 sq ft = 20.1 squares

Common pitches

angle, slope, factor

1/124.8°, 8%, factor 1.003
Too low for shingles
2/129.5°, 17%, factor 1.014
3/1214°, 25%, factor 1.031
4/1218.4°, 33%, factor 1.054
5/1222.6°, 42%, factor 1.083
6/1226.6°, 50%, factor 1.118
Yours
7/1230.3°, 58%, factor 1.158
8/1233.7°, 67%, factor 1.202
9/1236.9°, 75%, factor 1.250
10/1239.8°, 83%, factor 1.302
11/1242.5°, 92%, factor 1.357
12/1245°, 100%, factor 1.414
14/1249.4°, 117%, factor 1.537
16/1253.1°, 133%, factor 1.667
18/1256.3°, 150%, factor 1.803

The pitch factor times the footprint gives the roof surface. Hips and valleys add length, not area.

Shingles

Asphalt shingles are allowed from 2/12 up (IRC R905.2.2). Check the shingle maker’s instructions for the underlayment at your pitch.

Measuring it

Hold a level flat with one end touching the underside of a rafter, mark 12 in along the level, and measure straight up from that mark to the rafter: that’s the rise.

How we work it out

Pitch is how many inches the roof rises for every 12 inches it runs across. A 6/12 roof climbs 6 in each foot.

pitch = rise ÷ run × 12

angle = atan(pitch ÷ 12)

pitch factor = √(1 + (pitch ÷ 12)²)

The pitch factor is how much longer the slope is than the ground it covers. Multiply the roof's footprint, measured from above with the eaves, by it for the roof surface, and divide by 100 for roofing squares. Waste for cuts, hips and starter rows comes on top.

The address search reads the roof from USGS 3D Elevation Program lidar: laser points measured from a plane. Your browser downloads the points round the address, keeps the ones on flat, solid surfaces (leaves send back several echoes, roofs one), and grows them into faces. Each face's pitch comes from the plane fitted through its points. Each face's area is its share of the roof's outline from above. We checked both against two houses: the pitch and height match our lab pipeline (4/12, 25 ft), and the outlines came within 3% and 6% of the building outlines San Diego's regional planning agency traced from 2017 aerial photos.

Where the numbers come from

Then

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