Roof Pitch Calculator
Convert roof rise and run into pitch, angle, slope and rafter length. Estimate roof area and roofing squares.
Roof pitch
6:12
- Angle
- 26.6°
- Slope
- 50%
- Pitch multiplier
- 1.118
- Rafter length (ridge to wall + overhang)
- 14.42 ft
- Roof area
- 1,073.31 sq ft
- Roofing squares
- 10.7
Rafter length is measured from the ridge to the outside of the wall, plus the overhang. It does not include the ridge board or a birdsmouth cut.
Roof pitch is the rise over a 12-inch run, written as 6:12 or 6/12. The same slope can be described as an angle or a percentage, and the pitch multiplier converts a building footprint into sloped roof area.
This calculator also estimates rafter length from the building width and overhang. Use it for planning and material estimates; rafter spans, cuts and connections still need to follow the plans and local code.
How the roof pitch calculator works
Pitch = rise ÷ run × 12. Angle = arctangent(rise ÷ run). Pitch multiplier = √(rise² + run²) ÷ run. Rafter length = half the building width × multiplier + overhang. Roof area = building width × length × multiplier.
Worked example
A 6:12 roof has a 26.6° angle and a multiplier of 1.118. For a 24 × 40 ft building with a 12-inch overhang, the rafter is 12 × 1.118 + 1 = 14.4 ft, and the roof area is 24 × 40 × 1.118 = 1,073 sq ft.
How to measure roof pitch
- Hold a 12-inch level horizontally on the roof and measure the vertical rise at the 12-inch mark.
- If it is not safe to get on the roof, measure the rise and run from a gable end or use a pitch app from the ground.
- Pitch is rise over 12 inches of run; angle is the arctangent of the same ratio.
- A 4:12 roof rises 4 inches per foot; a 6:12 rises 6 inches per foot.
Pitch and roofing material
| Pitch | Angle | Typical roofing |
|---|---|---|
| 2:12–4:12 | 9.5°–18.4° | Low-slope membrane or rolled roofing; some shingles with special underlayment |
| 4:12–6:12 | 18.4°–26.6° | Asphalt shingles, metal, tile |
| 6:12–9:12 | 26.6°–36.9° | Standard steep-slope roofing |
| 9:12+ | 36.9°+ | Steep-slope; special safety and installation |
Walkability and safety
A 4:12 roof is walkable for many experienced roofers; 6:12 is steep and requires care; 8:12 and above usually needs roof jacks, a harness or staging. Never walk a wet or mossy roof.
Pitch also affects ventilation, snow shedding and gutter performance. A low-slope roof needs a drainage plan; a steep roof sheds water quickly but concentrates it at the eaves.
Frequently asked questions
What does a 6:12 roof pitch mean?
It rises 6 inches for every 12 inches of horizontal run, which is a 26.6° angle and a 50% slope. It is one of the most common residential roof pitches.
How do I calculate rafter length from pitch?
Multiply half the building width by the pitch multiplier, then add the overhang. For a 6:12 roof, the multiplier is 1.118, so a 12 ft half-span needs a 13.4 ft rafter before the overhang.
What is the pitch multiplier for a 4:12 roof?
About 1.054. For 6:12 it is 1.118, for 8:12 it is 1.202, and for 12:12 it is 1.414.
What roof pitch is walkable?
Up to 4:12 is generally manageable for experienced workers. 6:12 is steep, and 8:12 or higher usually requires fall protection. Conditions matter as much as the number.
How do I find the roof area from the footprint?
Multiply the building footprint by the pitch multiplier. A 1,000 sq ft footprint with a 6:12 roof has about 1,118 sq ft of roof area, before waste and overhangs.
Can asphalt shingles be used on a 2:12 roof?
Most shingle manufacturers require a minimum slope of 2:12 with a double underlayment, and some require 4:12. Below that, use a low-slope membrane or metal system.
Assumptions and accuracy
- Dimensions are converted to feet before the calculation; 1 ft = 12 in = 0.3048 m.
- Waste allowances are estimates. Add more for irregular shapes, many cuts and uneven subgrade.
- Bag yields, coverage rates and material densities vary by product. Check the label or ask your supplier.
- Local building codes and site conditions always take precedence over a general-purpose calculator.
- Read our full methodology