Roof sheet calculator: sheets, screws and flashing

How it works

Enter each roof plane separately. For each plane, measure the length along the ridge, the horizontal eave-to-ridge run and the roof pitch. The calculator adjusts the horizontal run to an approximate rafter length, then estimates sheets across using the selected profile’s effective cover width.

The example profile is LYSAGHT TRIMDEK with 762 mm cover width and a 2° minimum pitch. Select a support spacing listed in the manufacturer fastening schedule, the calculator uses its corresponding screw rate. The maximum sheet length, sheet end lap and flashing stock length come from your supplier or project, so enter those values rather than relying on an assumed universal stock size.

Enter ridge and barge flashing runs only when you have measured them. A roof shape can include hips, valleys, dormers and returns that cannot be inferred from plane dimensions alone.

Formula

• Convert run to sheet length

  Rafter length = horizontal run ÷ cos(pitch)

  Pitch is entered in degrees. This treats each plane as a straight slope.

• Estimate sheet count and end laps

  Sheets across = ceil(ridge length ÷ profile cover width) Sections down = smallest N where N × max sheet length − (N − 1) × end lap ≥ rafter length

  Extra sections overlap by the end lap you entered. Supplier cutting plans may change the exact section lengths.

• Estimate screws

  Screws = ceil(total roof area × sourced screws per m² × (1 + waste %))

  The sourced rate is selected from the LYSAGHT fastening schedule for the support spacing entered.

Worked example

1. 1

   Find the slope length

   4 m ÷ cos(25°) = 4.413 m per plane

   Example: a symmetrical gable has two planes, each 9 m along the ridge with a 4 m horizontal run.

2. 2

   Count sheet widths

   ceil(9 m ÷ 0.762 m) = 12 sheets across each plane 12 × 2 planes = 24 sheet pieces

   The supplier maximum is 6 m, so this example does not need an end lap.

3. 3

   Estimate fasteners

   Roof area = 2 × 9 m × 4.413 m ≈ 79.44 m² ceil(79.44 m² × 5 screws/m²) = 398 screws

   A 1,200 mm support spacing uses the cited 5 screws/m² entry. Waste is zero for this example.

Assumptions and safety

This calculator covers one sourced profile only. The cover width and minimum pitch are product-specific, and the screw table is specific to the cited LYSAGHT guide. Do not apply these values to another sheet profile. Actual fixing schedules may also depend on wind classification, building height, edge zones, support material and local design requirements.

No universal maximum sheet length or end lap is assumed. Obtain the cut length, end-lap detail and handling limits from your supplier. This estimate does not size purlins, rafters, trusses, connections or flashings, and it does not calculate valleys, hips, gutters, ridges, openings or roof penetrations.

The capping stock count uses the entered stock length and overlap. Confirm flashing profile, lap treatment and fixing details with the product supplier. Working at height can cause serious injury, use appropriate access equipment and fall protection, and have installation planned by a qualified roofer.

Frequently asked questions