BuildCalc Guides · Roofing
How to Figure Roof Pitch
Pitch is the most-quoted roof measurement and the most-confused. Here is how to measure it, what the numbers mean, and how to use it for material math.
How to measure pitch (from inside the attic)
- Step 1: hold a 24 inch level horizontally against the bottom edge of any rafter.
- Step 2: from the point 12 inches out along the level, measure straight up to the underside of the rafter.
- Step 3: read the vertical measurement in inches. That is the rise.
- Step 4: the pitch is that number over 12. 6 inches up = 6/12 pitch. 8 = 8/12. Done.
How to measure pitch (from outside)
- Step 1: from a safe spot like the rake board (gable end), hold a level horizontally against the underside of the soffit or the rake fascia.
- Step 2: at the 12 inch mark, measure straight up to the roof line.
- Step 3: read in inches as before.
- Alternative: use a digital angle finder or your phone's level app against a roof rafter. Read the angle in degrees, then convert: tan(angle) × 12 = pitch over 12.
Pitch reference table
Every common pitch, with the degree conversion and the surface-area multiplier you apply to footprint.
| Pitch | Degrees | Multiplier | Use |
|---|---|---|---|
| 2/12 | 9.5° | 1.014 | low slope — needs ice/water everywhere |
| 4/12 | 18.4° | 1.054 | minimum for asphalt shingles |
| 5/12 | 22.6° | 1.083 | common ranch/contemporary |
| 6/12 | 26.6° | 1.118 | most common residential |
| 7/12 | 30.3° | 1.158 | colonial, traditional |
| 8/12 | 33.7° | 1.202 | limit for safe walking |
| 9/12 | 36.9° | 1.250 | steep architectural |
| 10/12 | 39.8° | 1.302 | roofing-jack territory |
| 12/12 | 45.0° | 1.414 | A-frame, Cape Cod |
Using the pitch multiplier
When you measure a house from the ground, you get the footprint — but a roof is angled, so it has more surface area than its footprint:
- Footprint area × pitch multiplier = actual roof surface area.
- Example: a 30 × 40 ft house = 1,200 sq ft footprint. At 6/12 pitch: 1,200 × 1.118 = 1,342 sq ft of roof.
- Convert to squares (100 sq ft each): 1,342 ÷ 100 = 13.4 squares of shingles.
- With 10% waste: 13.4 × 1.10 = 14.8 squares = 45 bundles of architectural shingles (3 per square).
Why pitch matters
- Material selection. Below 4/12, you can't use standard asphalt shingles. Below 2/12 you need rolled roofing, TPO, EPDM, or built-up roofing.
- Walkability. Up to 6/12 most roofers can walk it. 6/12 to 8/12 needs care. Above 8/12 you need roofing jacks or harnesses.
- Waste factor. Steeper roofs scuff and break shingles when dragged up the slope — add 5 percent more waste for pitches over 8/12.
- Attic space. A 6/12 pitch over a 30 ft wide house gives ~7.5 ft of peak attic height. Lower pitches give cramped attics; higher pitches give walkable storage or even living space.
Calculate roof area
BuildCalc's roofing calculator takes footprint and pitch, applies the multiplier, and returns actual surface area, squares, shingle bundles and live material cost.
Open the roofing calculator →FAQ
How do you measure roof pitch?+
Easiest from inside the attic: hold a level against the bottom of a rafter, slide it out 12 inches horizontally, then measure straight up to the rafter. The vertical measurement in inches is your rise — that number over 12 is the pitch (e.g., 6 inches up = 6/12 pitch).
What is the most common residential roof pitch?+
6/12 is the most common residential pitch in the U.S. — it sheds water well, allows shingles in all standard widths, and gives enough attic height for storage and HVAC equipment. 4/12 is the minimum for asphalt shingles. 8/12 to 12/12 are common on steeper architectural styles.
How do you convert roof pitch to degrees?+
Take the arctangent of (rise ÷ run). For 6/12: arctan(6/12) = arctan(0.5) = 26.57°. Common conversions: 4/12 = 18.4°, 6/12 = 26.6°, 8/12 = 33.7°, 10/12 = 39.8°, 12/12 = 45°.
What is the pitch multiplier and why does it matter?+
The pitch multiplier converts horizontal (footprint) area to actual roof surface area. For 6/12 it is 1.118 — meaning a 1,000 sq ft footprint is actually 1,118 sq ft of roof surface. You need actual surface area, not footprint, when ordering shingles, underlayment or sheathing.
What is the lowest pitch you can shingle?+
4/12 is the minimum slope for asphalt shingles per IRC. From 2/12 to 4/12 you can use shingles only with a doubled underlayment system (ice-and-water shield over the entire roof). Below 2/12 you need a low-slope system: rolled roofing, modified bitumen, TPO, or EPDM.
Is there a roof pitch app or tool I can use on my phone?+
Yes — most smartphones have a level/angle app built in that can read degrees if you hold the phone flat against a roof rafter or rake board. Convert degrees back to pitch with tan(angle) × 12. A 26.6° reading is tan(26.6) × 12 = 6.0, so 6/12 pitch.
Related guides
- How many bundles of shingles for 1,000 sq ft? — applies the pitch math to a real order.
- How many square feet in an acre? — the other most-searched area conversion.