01
Measure the Roof Plan
Start with the horizontal length and width of the roof footprint.
Plan area = Length × Width
Roofing Tool
Roofing Calculator
Estimate roof area, pitch adjustment, waste allowance and material cost.
Metric Calculator
How this calculator works
Roof plan area is calculated from horizontal roof length × width.
Pitch multiplier is calculated from the entered roof rise per 12 units of run.
Plan area is multiplied by the pitch multiplier to estimate the sloped roof surface area.
Waste allowance is added to the sloped area before the final roofing area is calculated.
Estimated cost is final roofing area × price per square metre.
ROOFING PLANNING GUIDE
Plan Roofing Area, Pitch, Waste and Cost With Confidence
Measure the horizontal roof plan, account for roof pitch, add a practical waste allowance, and estimate the material area and cost before ordering.
02
Enter the Roof Pitch
Use the vertical rise for every 12 units of horizontal run.
Pitch multiplier = √(1 + (Rise ÷ 12)²)
03
Calculate Sloped Area
Apply the pitch multiplier to the horizontal plan area.
Sloped area = Plan area × Pitch multiplier
04
Add Waste Allowance
Allow extra material for cuts, overlaps and normal site variation.
Final area = Sloped area × (1 + Waste ÷ 100)
05
Check the Waste Area
See how much additional roofing area is included by the allowance.
Waste area = Final area − Sloped area
06
Estimate Material Cost
Use your supplier's price per square metre for a material estimate.
Roofing cost = Final area × Price per m²
Before You Order Roofing
Confirm the actual roof geometry, pitch and supplier coverage before purchasing materials. Hips, valleys, dormers, overlaps and complex roof sections may require additional allowance.
This calculator estimates roofing material area and cost only. Structural design, underlayment, flashing, fasteners, labour and other project requirements should be checked separately.