Roof Pitch Calculator
Convert rise and run into roof pitch (x/12), angle in degrees, slope percent and rafter length — the four ways a roof's steepness is described.
What is roof pitch?
Roof pitch describes steepness as a ratio: how many inches the roof rises for every 12 inches of horizontal run. A “6/12 pitch” climbs 6 inches per foot of run. The same steepness is also quoted as an angle in degrees, a slope in percent, and a rafter length — four languages for one roof, and this calculator translates between all of them.
Angle = arctan(rise ÷ run) · Slope % = rise ÷ run × 100 · Rafter = √(rise² + run²)
Example: a rise of 6 over a run of 12 is a 6/12 pitch = 26.57° = a 50% slope, and the rafter covering that run is √180 = 13.42 in long — a slope factor of 1.118, the multiplier roofing estimates are built on.
How to measure your pitch
From inside the attic or at a gable end: hold a spirit level horizontally against a rafter, mark 12 inches along the level from the rafter, then measure straight down from that mark to the rafter. That vertical measurement is your rise. No ladder gymnastics needed, and no guessing from the street.
| Pitch | Angle | Common use |
|---|
| 3/12 | 14.0° | Low-slope roofing, porches |
| 4/12 | 18.4° | Minimum for standard shingles on many specs |
| 6/12 | 26.6° | Typical house roof |
| 8/12 | 33.7° | Steep — walkable with care and boards |
| 12/12 | 45° | Very steep, classic A-frame territory |
This is a dimension tool — there is nothing to buy and no waste allowance, just the geometry. When you know your pitch, the roofing calculator turns it into squares, bundles and rolls.
Frequently asked questions
Is pitch the same as slope?
They describe the same steepness differently. Pitch is the rise-over-run ratio (6/12); slope is often quoted as that same ratio or as a percent (50%). Angle in degrees is the third dialect. Building suppliers in North America mostly speak pitch.
What pitch do I need for shingles?
Most asphalt shingle makers want at least 4/12 for standard installation; 2/12 to 4/12 needs special underlayment and low-slope application; below 2/12 belongs to membrane roofing. Check the wrapper of the shingle you plan to use.
How long is my rafter?
For a simple gable roof, the rafter for each 12 in of horizontal run is √(rise² + 144) inches — the calculator shows it for your exact rise and run. Add the overhang (eaves) length along the same slope when you cut real rafters.
Can I measure pitch from the ground?
Phone inclinometer apps against a gable end get you within a degree or two — fine for an estimate. For ordering roofing, measure properly from a rafter or the roof deck as described here.
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