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Quick answer
A 6:12 slope rises 6 units for every 12 horizontal units. It is 50% slope and about 26.565°, not 6° or 50°. At 5°, the rise over a 4 m horizontal run is about 0.349955 m. These are geometric examples, not permitted roof pitches.
How it works
Use the Roof Pitch Calculator South Africa to convert measured rise and horizontal run, degrees, percentage slope or rise per 12 units. Check the geometric sloping line and, optionally, convert a complete horizontal roof projection to sloping area.
Formula
Angle in degrees = atan(vertical rise ÷ horizontal run) × 180/π. Percentage slope = rise ÷ run × 100. Rise per 12 = rise ÷ run × 12. Sloping area = horizontal projection area ÷ cos(angle).
Assumptions and common mistakes
Check units, input values and the method before relying on an estimate. Review the existing tool notes and official sources below.
Formula
Angle in degrees = atan(vertical rise ÷ horizontal run) × 180/π. Percentage slope = rise ÷ run × 100. Rise per 12 = rise ÷ run × 12. Sloping area = horizontal projection area ÷ cos(angle).
| Conversion | Formula |
|---|---|
| Degrees | atan(rise/run) × 180/π |
| Percentage slope | 100 × rise/run |
| Rise per 12 | 12 × rise/run |
| Geometric slope | √(run² + rise²) |
| Sloping area | Horizontal roof projection ÷ cos(angle) |
What is roof pitch?
In this calculator, pitch describes roof slope as rise over horizontal run, with equivalent angle and percentage. A pitched roof has sloping roof planes. A mono-pitch roof has one main sloping plane, while a simple gable has two main slopes. The roof shape and angle do not by themselves establish covering suitability or structural design.
How to calculate roof pitch in degrees
Measure vertical rise over a known horizontal run. Divide rise by run, take the inverse tangent, then convert radians to degrees. The tool accepts independent units for rise and run and converts them before dividing. Run must be positive; a zero rise gives zero geometric slope. The supported range is 0–85° for calculation, not a statement that every angle is suitable for roofing.
Run, span and mono-pitch roofs
Run is the horizontal distance for the particular sloping plane being measured, not the sloping line length. In a symmetrical gable, an eave-to-ridge run may be half the building span; do not halve a measured run again. For mono-pitch geometry, use the horizontal distance between the chosen low and high points. Existing dimensions, wall supports and connections require their own assessment.
6:12 pitch, percentage and degrees
A 6:12 slope is 6 ÷ 12 = 0.5 rise/run, so its percentage slope is 50% and its angle is about 26.565°. A 100% slope is 45°, not 100°. The ratio uses matching units and does not have to be measured in inches. Enter the rise per 12 horizontal units or select percentage or degrees directly.
How to work out 5 degree roof pitch
Use rise = horizontal run × tan(5°). For a hypothetical 4 m run, rise is about 0.349955 m, equivalent to an 8.748866% slope. The geometric sloping line is about 4.015279 m before any extra overhang. These values show arithmetic and do not approve a 5° roof for a selected sheet, tile, membrane or exposure.
Roof area with pitch and overhangs
For one common pitch, divide the complete horizontal roof projection by cosine of the angle. A hypothetical 100 m² projection at 30° is about 115.470054 m² sloping area. Include overhangs in that area input and do not correct an already sloping area again. The separate additional-overhang field extends only the calculated line at the same pitch. Different pitches need separate plane areas. Profile development, waste and accessories are separate quantities.
How to measure or check roof pitch
Use suitable plans or a measured vertical rise and horizontal run available from an accessible location. Check that the dimensions describe the same plane and measurement points. A sloping tape length is not horizontal run. Arrange a competent survey where access or geometry is uncertain. The calculator does not require roof access, determine measurement accuracy or turn a line length into a timber cutting schedule.
Lowest pitch, flat roof changes and solar panels
There is no universal lowest pitch for every metal sheet or tile. Confirm the exact covering, slope length, laps, exposure and manufacturer requirements. Converting an existing flat roof to a pitched or mono-pitch roof needs design and support, drainage, connection and approval assessment. Solar-panel tilt is also affected by location, orientation, shading, roof capacity and mounting design; roof pitch alone does not determine one best angle.
Copy, print and roof pitch PDF
Copy the calculated result, download the CSV snapshot or use Print / save PDF and choose PDF in a supported browser print dialog. The export is a record of entered geometry, not a certified survey, design drawing or standalone installation guide. Use the related Roof Tile and Roof Cost calculators only after the geometry and product specifications are confirmed.
Reviewed by the 99tools team. Editorial and corrections policy.
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Frequently asked questions
How do I calculate roof pitch in degrees?
Use atan(vertical rise ÷ horizontal run), then convert to degrees. Use matching units or select each dimension unit correctly.
What is a 6:12 roof pitch?
It rises 6 units over 12 horizontal units, equal to 50% slope and about 26.565°.
How much rise is a 5 degree pitch?
Rise equals horizontal run × tan(5°). A 4 m run gives about 0.349955 m rise.
How do I calculate roof area with pitch?
For a common pitch, divide the complete horizontal roof projection by cos(angle). Different pitches need separate plane calculations.
What is a mono-pitch roof?
It has one main sloping roof plane. Use the actual horizontal distance and vertical rise for the measured plane.
What is the lowest pitch for a metal roof?
It depends on the exact product, slope length, laps, exposure and specified system. This calculator does not choose a minimum pitch.
What roof pitch is best for solar panels?
There is no single answer from roof pitch alone. Location, orientation, shading, desired production, roof capacity and mounting all matter.
Can I save a roof pitch calculation as PDF?
Use Print / save PDF and choose a PDF destination if your browser supports it. The result is a geometry snapshot, not a certified design.
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Helpful guides
How to Calculate Roof Pitch in Degrees
Convert measured rise and horizontal run into degrees, percentage slope and rise-per-12 notation without confusing the units.
Roof Area, Pitch Limits and Solar Planning
Correct horizontal roof area once and check the exact covering and solar design instead of assuming one universal roof angle.