Convert between roof pitch and angle, then get rafter length, ridge height and total roofing area.
The method behind this calculator
Roof pitch is written as rise over a twelve-inch run — a 6:12 roof rises six inches for every foot of horizontal travel. That convention exists because it makes framing arithmetic easy on site.
The slope factor is the number that turns a flat footprint into actual roof area. It is always greater than one, which is why a steep roof needs considerably more material than its floor plan suggests.
How to fill it in
- Enter the pitch as rise in twelve, or switch to degrees.
- Enter the building span and length.
- Add the overhang to get the full roof area.
The maths behind it
angle = arctan(rise ÷ 12)
slope factor = √(rise² + 12²) ÷ 12
roof area = footprint area × slope factor · one square = 100 ft²
Try it with these numbers
The calculator opens with a enter as of Rise over 12 inches of run, overhang per side of 12. On those figures the roof pitch is 6 : 12. Underneath, Angle comes out at 26.57° and Slope factor at 1.118. Change any field and every figure updates as you type.
Questions people ask about this
What is a standard roof pitch?
Most residential roofs fall between 4:12 and 9:12. Below 3:12 counts as low slope and usually needs a different roofing system.
How do I measure pitch on an existing roof?
Hold a level horizontally against a rafter, mark twelve inches along it, and measure straight down to the rafter. That drop is your rise.
Why is roof area larger than the floor area?
Because the roof surface is sloped. The slope factor converts the horizontal footprint into the true surface area.