Roof materials calculator
Estimate outputs: Area with allowance, Whole bundles, Underlay rolls, Whole gutter sections. Adjust Length, Width, Roof angle to match your project.
Estimate outputs: Area with allowance, Whole bundles, Underlay rolls, Whole gutter sections. Adjust Length, Width, Roof angle to match your project.
Inputs and units
Use the units shown beside each field. Replace the sample values with your measurements and the figures on the selected product packaging.
| Parameter | Example input |
|---|---|
| Length | 10 m |
| Width | 8 m |
| Roof angle | 30 ° |
| Coverage per bundle | 3 m² |
| Underlay coverage per roll | 40 m² |
| Stock piece length | 3 m |
| Waste allowance | 10 % |
Formula and assumptions
Area with allowanceLength × Width / cos(Roof angle × π / 180) × (1 + Waste allowance / 100)
Whole bundlesceil(Area with allowance / Coverage per bundle)
Underlay rollsceil(Area with allowance / Underlay coverage per roll)
Whole gutter sectionsceil(2 × Length × (1 + Waste allowance / 100) / Stock piece length)
ceil = round up; floor = round down; max = the greater value. Trigonometric angles are converted from degrees to radians.
Allowance is applied before rounding to whole packages. Whole units are rounded up; displayed decimals are rounded only for readability.
Project lists use simplified rectangular geometry. They do not include every fixing, fitting, accessory or labor cost.
Worked example
Sample values are examples, not product specifications. Run the calculation again with your own measurements.
| Result | Calculation |
|---|---|
| Area with allowance | 101.6136 m² |
| Whole bundles | 34 |
| Underlay rolls | 3 |
| Whole gutter sections | 8 |
Related calculators
Related tools use separate measurements. Check their inputs before transferring quantities.
These are quantity estimates. Confirm product coverage, site conditions and required dimensions before ordering.