Loan Roof Pitch Calculator
Pitch is three languages for one slope: 6/12, 26.57°, 50%. This calculator translates between all three, adds the area factor your material counts depend on, and gives rafter length per foot of run — from a rise, or back from an angle.
Measure rise in the attic: hold a 12-in level against a rafter, mark the level end, and measure straight down to the rafter. That drop is your rise. Phone inclinometer apps get within a step.
How it works
Pitch is a ratio: rise ÷ run, normalised to a 12-in run. The angle is arctan(rise ÷ 12); slope percent is simply rise ÷ 12 × 100. The number that costs money is the slope factor √(1 + (rise/12)²) — multiply a footprint or a horizontal run by it to get true roof area and true rafter length. At 6/12 the factor is 1.118: every 10 ft of run is 11.18 ft of rafter, and every 1,000 sq ft of house is 1,118 sq ft of roof.
Formula & worked example
Formula: Angle = arctan(rise ÷ 12); slope % = rise ÷ 12 × 100; roof-area and rafter factor = √(1 + (rise ÷ 12)²). From an angle: rise = tan(angle) × 12.
Worked example: A 6/12 pitch is 26.57°, a 50% slope, factor 1.118 — 13.42 in of rafter per foot of run. A 30° roof converts back to about 6.93/12 with a 1.155 factor.
When to use this
- Plans give degrees and your roofer speaks in x/12 — you need the translation.
- You measured a slope with a level in the attic and want the angle and area factor.
- You are converting footprint area into true roof area for materials.
How to use it, step by step
- Choose the starting point: rise per 12, or angle in degrees.
- Enter the one you have.
- Read all three languages — pitch, degrees, percent — plus the area factor.
- Use the factor on footprint area before ordering any roofing material.
What the inputs mean
| Input | What it is | Typical values |
|---|---|---|
| Rise per 12 | Vertical rise over a 12-in horizontal run | 4/12 low; 6/12 typical; 9–12/12 steep |
| Angle | Slope in degrees from horizontal | 18.4° = 4/12; 26.6° = 6/12; 45° = 12/12 |
Another worked example
Two reference points: a 4/12 pitch is 18.43° with a 1.054 factor (a 1,000 sq ft footprint hides only 54 extra sq ft of roof), while 9/12 is 36.87° with an exact 1.25 factor (the same footprint is 1,250 sq ft of roof — nearly two extra squares of shingles in the slope).
Frequently asked questions
What angle is a 6/12 pitch?
26.57 degrees — a 50% slope, with a 1.118 area factor. For comparison: 4/12 is 18.43° and a 1.054 factor; 9/12 is 36.87° and exactly 1.25; 12/12 is 45° and 1.414.
What pitch is a 30-degree roof?
About 6.93/12 — call it 7/12. A 30° angle is a 57.7% slope with a 1.155 area factor. Roofers order by the x/12 on the plans, so converting degrees back to rise (this tool's second mode) is the everyday direction.
How do I find rafter length from pitch?
Multiply the horizontal run by the slope factor. A 14-ft run at 6/12 needs 14 × 1.118 = 15.65 ft of rafter before overhang and ridge deductions — buy 16-ft stock. The table line in the results gives the factor per foot of run.
What is the minimum pitch for shingles?
Standard shingles want 4/12 or more; 2/12 to 4/12 is allowed with double underlayment or ice-and-water shield over the whole deck; below 2/12, shingles are out and membranes take over.
Why does pitch change my material count?
Because the roof is the hypotenuse. The same 1,200 sq ft footprint is 1,265 sq ft of roof at 4/12 and 1,500 at 9/12 — nearly two extra squares of shingles hiding in the slope.
🏠 Putting materials on that pitch?
Pitch in hand, the Roofing Estimator turns footprint + pitch into bundles, rolls and nails for the whole roof.
What pitch do most houses have?
Between 4/12 and 8/12 covers the large majority of US homes; 6/12 is the modal suburban roof. Below 4/12, shingle warranties and underlayment rules start changing.
How do I measure pitch from the ground?
A pitch-finder app on a phone held against a gable-end trim board gets within about half a step; for ordering accuracy, the attic method (12-in level on a rafter, measure the drop) is the one to trust.