Roof Pitch Calculator
Enter rise and run, or a pitch as x/12, to see the angle, percent slope, and walkability. A 6/12 pitch is 26.6 degrees and 50 percent slope. The diagram is a section through the roof, not a photo.
Roof pitch — 6/12, 26.6 degrees, 50.0 percent
| Pitch | 6/12 |
|---|---|
| Angle | 26.6 degrees |
| Percent slope | 50.0% |
| Area factor | 1.118 |
| sqrt(1 + (rise/run)²). Multiply footprint by this to get roof surface before waste. | |
| Walkability | Walkable |
| 4/12 to 6/12 is the common residential walking slope. PPE still applies. | |
Rate table updated September 2026. Previous: initial release.
This is a budget estimate, not a bid. Estimates were compiled in September 2026 from published U.S. cost guides. Final price depends on deck condition, penetrations, access, local code, and a contractor's on-site inspection.
What roof pitch means
Roof pitch in the U.S. is rise over run, written as x/12. The 12 is 12 inches of horizontal run. A 6/12 roof rises 6 inches for every 12 inches of run. That is a ratio, not a weather forecast and not a brand of shingle.
The angle of a 6/12 pitch is arctan(6/12), which is 26.6 degrees. The percent slope is (6/12) × 100, which is 50 percent. Those three numbers describe the same triangle. Crews talk in x/12. Inspectors sometimes write degrees. Drainage specs sometimes write percent.
Pitch also sets the area multiplier for a roof measured on the footprint. The factor is sqrt(1 + (rise/12)²). At 6/12 that factor is 1.118. A 2,000 sq ft rectangle of footprint becomes about 2,236 sq ft of roof surface before waste. At 12/12 the factor is 1.414. At 4/12 it is 1.054.
Pitch is not the same as roof complexity. A 6/12 gable and a 6/12 hip on the same rectangle have the same surface area. The hip has more ridges and more waste, which shows up on a cost sheet, not in the pitch triangle.
How to measure rise and run
From the attic, set a 12-inch level on the underside of a rafter, hold it flat, and measure vertically from the 12-inch mark up to the rafter. That vertical reading is rise. The 12-inch level is run. If the tape reads 6 inches, the pitch is 6/12.
From the ground you can measure a rake board the same way if you can reach it safely, or count courses of architectural shingles: many laminates expose 5-5/8 inches, so 12 inches of run is a little over two courses. That count is a field check, not a survey. A 1-inch error in rise on a 12-inch run is a full 1/12 of pitch.
This calculator accepts any rise and run in inches. A 4-inch rise on an 8-inch run is the same 6/12 as 6 and 12. If you already know the pitch as x/12, type that in the pitch field; the sheet sets run to 12 inches and rise to x.
Do not stand on a 10/12 or steeper roof to measure it. That slope is not walkable. Measure from inside, from a ladder on the gable, or from a plan.
Pitch, angle, and percent slope
Pitch x/12 = 12 × (rise ÷ run). Angle in degrees = arctan(rise ÷ run) × 180/π. Percent slope = (rise ÷ run) × 100. If run is 0 the sheet returns zeros; a vertical wall is not a roof pitch.
A 4/12 pitch is 18.4 degrees and 33.3 percent. An 8/12 pitch is 33.7 degrees and 66.7 percent. A 12/12 pitch is 45 degrees and 100 percent. Those values are geometry. They do not change with ZIP code or shingle color.
Percent slope is easy to mix up with pitch. A 6/12 roof is a 50 percent slope, not a 6 percent slope. Highway grades use percent; roofers do not say “50 percent roof” on a bid, they say 6/12.
The pitch factor table that area calculators use is the hypotenuse of this same triangle. You do not need a second formula. sqrt(1 + (6/12)²) is 1.118, which is why a 6/12 roof has about 12 percent more surface than its footprint.
Walkability and asphalt shingle minimums
Walkability here is a field rating, not an OSHA certificate. 4/12 to 6/12 is the slope most residential crews walk with PPE. 7/12 to 9/12 still gets walked, with extra fall protection. 10/12 and steeper is not a walkable roof; the labor row on the cost calculator uses a 1.40–1.80 staging multiplier for that reason.
Below 2/12, asphalt shingles are not permitted (IRC R905.2.2). Low-slope systems — TPO, EPDM, or modified bitumen — are the options here.
2/12 to 4/12 needs a double layer of underlayment under shingles. That adds underlayment material and labor; the sheet prices it 10% above the 4/12–6/12 row.
3/12 is above the 2/12 legal floor. It is not a reason to switch the house to TPO. It is a reason to budget a double underlayment layer and to read the shingle maker’s low-slope pages. 2/12 itself is the minimum asphalt-shingle slope in IRC R905.2.2 when that double underlayment and the manufacturer’s low-slope instructions are followed.
How pitch changes roof replacement cost
This page does not know your roof area. The cost block below uses an example 2,000 sq ft roof of architectural asphalt, one-layer tear-off, national average rates. At 6/12 that example is $10,300 – $17,000. Assumes a clean rectangle: no deck repair, one layer of penetrations, ground access.
At 3/12 the same example is $10,800 – $17,900 because labor is 10 percent above the 4/12–6/12 row for double underlayment. At 12/12 it is $12,900 – $24,900 because staging labor uses the 1.40–1.80 band. Material per square does not change with pitch. Labor does.
If the 2,000 sq ft is living area, not roof surface, convert it on the square footage calculator first. Pitch factor and waste live there. Then bring the pitch into the replacement calculator with the query string this page writes.
It is a budget estimate, not a bid. The cost numbers were compiled September 2026 from published U.S. cost guides, the same table as the home calculator.
Roof pitch calculator FAQ
What is a 6/12 roof pitch?
6 inches of rise for every 12 inches of run. That is 26.6 degrees, 50 percent slope, and a 1.118 area factor. It is the default pitch on this site because it is a common U.S. residential walking slope.
How do you calculate roof pitch from rise and run?
Pitch in x/12 = 12 × (rise ÷ run). Measure rise and run in the same unit, usually inches. A 6-inch rise on a 12-inch run is 6/12. A 4-inch rise on an 8-inch run is also 6/12.
What angle is a 6/12 pitch in degrees?
26.6 degrees. The formula is arctan(6/12) × 180/π. A 12/12 pitch is 45 degrees. A 4/12 pitch is 18.4 degrees.
Is 4/12 a steep roof pitch?
No. 4/12 sits at the bottom of the walkable band (4/12 to 6/12). Steep on this sheet starts at 10/12. 7/12 to 9/12 is caution, not steep.
What is the minimum roof pitch for asphalt shingles?
2/12 under IRC R905.2.2, with double underlayment and the manufacturer’s low-slope instructions. Below 2/12, asphalt shingles are not permitted. 4/12 and steeper is conventional single-underlayment work for most laminated shingles.
Is 3/12 pitch too low for asphalt shingles?
No. 3/12 is legal and can be warrantable. It needs a double layer of underlayment. It is not a membrane roof. Switching a 3/12 house to TPO because of pitch alone adds cost the code does not require.
How does roof pitch affect replacement cost?
Labor, not the asphalt price per square. On the example 2,000 sq ft architectural roof, 6/12 is $10,300 – $17,000, 3/12 is $10,800 – $17,900, and 12/12 is $12,900 – $24,900, all with one-layer tear-off at national average rates.
What does walkability mean on a roof?
Whether a crew can walk the slope with PPE, or needs staging. It is a field rating. 4/12–6/12 walkable, 7/12–9/12 caution, 10/12 and up not walkable. It is not an OSHA card and not a warranty.