Include the overhang
Roof coverings extend beyond the wall line. The eaves overhang is added to both sides of each footprint dimension.
Free South African roof calculator
Roof area calculator.
Measure true pitch.
Calculate roof pitch, sloped area, rafter length, gutters and practical tile or sheet quantities before you quote or buy.
Measure your roof ↓Metric. Clear assumptions.
⌁Pitch conversionsDegrees, percentage and rise/run
□True sloped areaOverhang and waste included
≋Material planningTiles or roof sheets
⌜Roof dimensionsSlope, ridge and gutters
01
Roof form
Which roof are you measuring?
Select the closest simple roof shape. Complex roofs should be divided into separate rectangles and calculated face by face.
03
The geometry
How true roof area is calculated
The footprint is only the horizontal projection. Pitch increases the actual surface that must be covered or coated.
01 · Plan dimensions(Length + overhangs) × (Width + overhangs)
÷02 · Pitch factorcos (roof angle)
=03 · True roof areaActual sloped m²
Convert the pitch
The angle becomes a slope factor. The steeper the roof, the larger its true area compared with its plan area.
Add an order allowance
Laps, cuts, breakages and detail work require more material than the clean geometric area alone.
Confirm the profile
Tiles per square metre and sheet cover widths vary. Always use the selected manufacturer’s technical data before ordering.
Measure safely
Most roofs can be estimated from the ground.
Use building dimensions, drawings or a safe laser measurement. Do not climb onto a wet, fragile, steep or unprotected roof to use this calculator.
Request a roof assessment →Good to know
Roof calculator FAQs
How do I calculate roof area from floor area?+
Add the roof overhangs to the building footprint, then divide the resulting plan area by the cosine of the roof angle. Floor area alone usually excludes eaves and does not account for pitch.
What is a typical roof pitch in South Africa?+
There is no single standard pitch. It depends on roof covering, design, wind exposure and manufacturer requirements. Many pitched residential roofs fall around 20–35°, but the selected product’s minimum pitch must govern.
What does effective sheet cover width mean?+
It is the width that one installed sheet covers after the required side lap. It is smaller than the sheet’s full manufactured width and varies by roof profile.
Can I use this for a hip or valley roof?+
The area estimate can help with a simple rectangular hip roof. For valleys, intersecting roofs, dormers or irregular footprints, divide the roof into separate faces and obtain a proper take-off before ordering.