What do you know about the roof?
Roof dimensions
Roof type
m
m
For a gable roof, half the entered width is used as the horizontal run from wall plate to ridge.
m
Height difference from the wall plate to the ridge or highest edge of a mono-pitch roof.
°
%
A 50% pitch rises 0.5 m for every 1 m of horizontal run.
Roof overhangsOverhangs change the covering area, not the building geometry
m
Horizontal projection beyond the wall at each eaves edge.
m
Roof extension beyond each gable end.
Results
Roof pitch angle26.6°50.0% pitch · ratio 1 : 2
Symmetrical gable roof8 × 10 m building
26.6°The diagram is proportional to the dimensions entered and marks the building width, rise and one rafter length.
Calculation summary
- Horizontal run to ridge
- 4.00 m
- Vertical rise
- 2.00 m
- Pitch percentage
- 50.0 %
- Pitch ratio
- 1 : 2
- Roof length including verge overhangs
- 10.60 m
- Area including 10% allowance
- 114.71 m²
Formula used: √(4² + 2²) × 10 × 2 = 89.44 m²
Results are intended for geometry and preliminary material-area estimates. Structural design and product-specific installation requirements must be checked against the plans and manufacturer guidance.
Quick conversion
Roof pitch in degrees and percent
Pitch percentage shows the vertical rise per 100 horizontal units. Select an angle to use it in the calculator.
| Angle | Pitch | Rise per 1 m | |
|---|---|---|---|
| 5° | 8.7 % | 8.7 cm | |
| 10° | 17.6 % | 17.6 cm | |
| 15° | 26.8 % | 26.8 cm | |
| 20° | 36.4 % | 36.4 cm | |
| 25° | 46.6 % | 46.6 cm | |
| 30° | 57.7 % | 57.7 cm | |
| 35° | 70.0 % | 70.0 cm | |
| 40° | 83.9 % | 83.9 cm | |
| 45° | 100.0 % | 100.0 cm |
Conversions use standard trigonometry: pitch (%) = tan(angle) × 100. Always check the minimum pitch required by the selected roofing product.
From measurements to area
How to use the roof pitch calculator
Only a few dimensions are needed, but measure them consistently and distinguish horizontal run from sloping length.
Choose the roof type
Gable mode assumes a centred ridge and divides the building width by two. Mono-pitch mode uses the full width.
Enter the pitch you know
Use vertical rise, angle in degrees or percentage pitch. The other values are calculated automatically.
Add the overhangs
Eaves overhang is measured horizontally; verge overhang is measured along the building. Both are included in covering area.
Allow for roofing material
A 10% allowance is added to the final covering area without changing the roof geometry.
Calculating roof pitch from rise
Roof pitch requires two perpendicular measurements: vertical rise and horizontal run. On a symmetrical gable roof, the run from wall plate to ridge is half the building width.
For an 8 m wide roof with a ridge 2 m above the wall plates, the run is 4 m. The angle is arctan(2 ÷ 4) ≈ 26.6° and the pitch is 50%.
Rafter length and roof area
Run and rise form a right-angled triangle. The geometric rafter length is √(run² + rise²).
For each rectangular roof slope, multiply sloping length by roof length. Double it for a gable roof. Overhangs are included in covering area, followed by a separate 10% allowance.
Frequently asked questions about roof pitch
Answers about roof angles, percentage pitch, rafter length, overhangs and roof area.
Measure the vertical rise and horizontal run from wall plate to ridge. The angle is arctan(rise ÷ run). For a symmetrical gable roof, the run is half the building width.
Multiply the tangent of the angle by 100. A 45° roof is a 100% pitch, while 30° is about 57.7%.
The geometric length is found with Pythagoras: √(run² + rise²). It excludes the overhang, ridge thickness and any birdsmouth or construction deductions.
One sloping length is multiplied by the building length and then doubled. The calculator shows a separate covering area including overhangs.
No. Calculate each unequal side separately as a mono-pitch roof.
No. It provides geometry only. A competent designer must specify rafter section, spacing, bearings and fixings for the actual loads and regulations.