About this calculator
Convert any way of stating roof pitch into the others. SANS 10400-L and South African tile and sheet makers state pitch in degrees. This also gives the pitch factor for converting plan area to roof area.
How it’s calculated
Slope t = rise ÷ run. Degrees = atan(t). x/12 = t × 12. Percent = t × 100. Pitch factor = √(1 + t²). Hip/valley factor (per unit of common run) = √(2 + t²).
Worked example
With these inputs:
- I know
- Angle in degrees
- Degrees
- 30
the result is:
- Pitch
- 6.93/12 = 30°
- Degrees
- 30°
- Pitch (x in 12)
- 6.93 in 12
- Percent grade
- 57.7%
- Ratio
- 1 : 1.73
Tips from the trade
- To measure pitch, hold a level horizontally against the roof and measure 1 m along it. The vertical gap down to the roof is the rise.
- From inside the roof space, measure the rafter angle with a digital angle finder.
Common questions
What is a 22.5° roof as a ratio?
It rises about 414 mm for every metre of run (tan 22.5° = 0.414), about 1 in 2.4.
What is the minimum pitch for a tiled roof?
Under SANS 10400-L table 2, concrete and clay tiles need at least 17° with an approved underlay and 26° without.
Results are estimates for planning and pricing. Check quantities against your drawings, the manufacturer’s data and SANS 10400 (the National Building Regulations) and your local municipality before ordering.