Name the quantity before entering a number
Roof pitch can be stated as rise per twelve units, an angle or percent grade. These are related, but the same number has different meanings in each system. In the roof pitch calculator, choose the known measurement first so the field label describes what you are entering.
A 6:12 pitch rises six units over twelve horizontally. Its grade is 50%, while its angle is about 26.565°. Treating that 50 as degrees would describe a much steeper slope.
Measure horizontal run
Run is the horizontal side of the right triangle. Slope length is the diagonal. If you have measured along an inclined surface, do not enter that length as run without converting the geometry.
For rise 1.5 m and run 3 m, the diagonal is about 3.3541 m. The calculator can show this only when a physical run is supplied. A pitch ratio alone gives shape, not a unique rafter length.
Use the multiplier for a matching area question
The slope multiplier is the diagonal divided by horizontal run. It converts an appropriately measured projected area to its equal-pitch surface equivalent. It does not add overhangs, dormers or a second measured section automatically.
If an area is already measured on the slope, applying the multiplier again would overstate it. Mark the measurement basis in the exported report before comparing estimates.
Transfer geometry without transferring assumptions
The roofing material calculator uses useful pack coverage and a chosen allowance after the roof area is known. Those are separate product decisions. Pitch conversion alone does not determine which product is suitable or how much cutting loss is expected.
Use the diagram to review the relationship between rise, run and slope. Confirm real dimensions and the project specification separately; this tool does not design a roof structure or select an approved minimum pitch.