Roof Pitch Calculator

Ratio

6.00 : 12

metric form 1 : 2.00

Angle

26.57°

atan(0.5000)

Slope

50.00%

0.5000 × 100

Slope factor

1.1180

√(1 + 0.500²) = 1 / cos θ

Roof dimensions

The conversion maths, spelled out

1. Pitch ratio → angle: atan(6.00 / 12) = atan(0.5000) = 26.57°
2. Pitch ratio → slope: (6.00 / 12) × 100 = 50.00%
3. Angle → ratio: 12 × tan(26.57°) = 6.00 : 12
4. Slope → ratio: 12 × 50.00 / 100 = 6.00 : 12
5. Slope factor: 1 / cos(26.57°) = √(1 + 0.5000²) = 1.1180
6. Rise: run 4.00 m × 0.5000 = 2.00 m
7. Rafter: run 4.00 m × slope factor 1.1180 = 4.47 m
8. Area: 2 slopes × ((4.00 m + 0.45 m) × 1.1180) × 10.60 m = 105.5 m²
9. Squares: 105.5 m² ÷ 9.290 m² = 11.35 squares

One roofing square is 100 square feet, which is 9.2903 m² — the bridge between the metric area and the number of bundles your supplier quotes.

Dimensioned cross-section

The right triangle of one slope, drawn to scale, with the eaves overhang shown beyond the wall plate.

Rafter length is the geometric line from the wall plate to the ridge. Add for the plumb cut at the ridge and the seat cut at the plate — usually 150–300 mm (6–12 in) in total — and remember the eaves overhang is measured horizontally, so its rafter length is the overhang times the slope factor.

About this tool

Pitch is stored as a single ratio, so editing the ratio, the angle or the percentage updates the other two exactly rather than by re-rounding. From that ratio it derives the rise, rafter length, ridge height and true sloped roof area including eaves and gable overhangs, then converts the area into roofing squares (100 sq ft each, 9.2903 m²) and shingle bundles. Metric and imperial lengths both work. Everything runs in your browser; nothing is uploaded.