Roof Pitch Calculator NZ
The QuoteCore+ free NZ roof pitch calculator converts roof pitch between degrees, rise/run ratio and percentage. Enter any one value and it converts instantly. Includes the pitch factor for turning plan area into actual roof surface area. Free, no signup.
Rafter / Hip & Valley
Calculate rafter and hip/valley lengths from pitch and span
Bearing width on the wall plate (plate width is a common choice)
Timber depth - used to check the ⅓ maximum notch rule
Angle measured from horizontal.
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Roof pitch - did you know?
What exactly is roof pitch?
Roof pitch is the steepness of a roof, expressed as an angle in degrees or as a ratio of rise to run. NZ roofers commonly use degrees (e.g. 35°); the ratio form (e.g. 6:12) is more common in the US. Both describe the same thing.
Degrees vs ratio conversion
To convert ratio to degrees: pitch° = arctan(rise ÷ run). A 6:12 roof = arctan(0.5) = 26.57°. To convert degrees to ratio: tan(pitch°). At 35°, tan(35) = 0.700, so the ratio is ~7:10.
Why pitch matters for materials
Pitch determines roof surface area. The pitch factor (1 ÷ cos(pitch°)) converts plan area to actual roof area. At 35°, the factor is 1.221 - 100 m² plan becomes 122.1 m² of roof surface.
Minimum pitch by material
Common NZ minimums: long-run steel and corrugated iron typically 3°+ (profile-dependent, check the manufacturer); concrete/clay tiles generally 17.5°+; membrane flat roofs need a 1:80 fall (~0.7°). Below minimums, water ponds and penetrates.
Formulas used
Pitch from rise/run
pitch° = arctan(rise ÷ run)
Rise/run from pitch
ratio = tan(pitch°)
Pitch as percentage
percent = (rise ÷ run) × 100
Pitch factor
factor = 1 ÷ cos(pitch°)
Frequently asked questions
How do I calculate roof pitch in degrees?
Measure rise over a known run (e.g. 300mm over 1000mm) and calculate arctan(0.3) = 16.7°. Or use a digital level on the roof surface.
What is a 6:12 pitch in degrees?
arctan(6/12) = 26.57° - a common residential roof pitch in parts of the US; NZ roofs are usually specced directly in degrees.
What pitch factor should I use?
1 ÷ cos(pitch°). At 25° = 1.103, at 35° = 1.221, at 45° = 1.414. Multiply plan area by this factor for actual roof surface area.
Is this roof pitch calculator free?
Yes - it converts between degrees, ratios and percentages and shows the pitch factor, free with no signup. Built for NZ roofs and metric measurements.