Polycarbonate Roof Calculator

Enter your roof size and we’ll recommend the best sheet setup, calculate the full kit, and show a quote you can add to basket.

We’ll calculate how many sheets you need plus glazing bars, trims, fixings, and breather tape. For attached roofs we’ll also include wall flashing tape. You’ll see your quote like a basket with product images, an estimated total, and an estimated delivery window (3–5 working days).

Step 1 of 3 Roof details

Roof details

Width = left to right.
Attached: wall → front. Free standing: front → back.
Measurement diagram
Tip: measure the internal frame where the sheets sit.

Sheet options

Recommended thickness: 16mm
Sheet colour
Sheet size
Auto-optimise chooses sizes to minimise waste.
Auto selected: —
Switch to manual sizes if you prefer.
Accessory colour

Your quote

Estimated total
£0.00
✅ UK Stock
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✅ Cut to size available

Your kit will appear here once we calculate it.

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Polycarbonate Roof Sheet Calculator

Planning a new pergola, carport, lean-to or garden canopy?
Use this simple polycarbonate roof sheet calculator to work out how many multiwall polycarbonate sheets you need, along with the right accessories to finish the job properly.

Once you’ve got your result, you can add the sheets straight to your basket from our Multiwall Polycarbonate Sheets range and get them delivered in 3–5 working days.

How the Polycarbonate Roof Calculator Works

Our calculator is designed around the way multiwall polycarbonate is normally installed in the UK:

  • Sheets usually run down the slope of the roof
  • Sheet length = the length of your roof
  • Number of sheets = roof width ÷ sheet width

You only need three measurements:

  1. Total roof width (mm)
  2. Total roof length (mm)
  3. Your chosen sheet width and thickness

The calculator then works out:

  • How many sheets you need
  • An example layout
  • Recommended accessories

Enter Your Roof Measurements

You’ll need:

  • A tape measure
  • The planned external size of your structure
  • Your preferred sheet thickness (10mm, 16mm or 25mm)

👉 Tip: It’s usually easiest to measure in millimetres (mm).

Example Calculations

Example 1 – Small Pergola

  • Roof width: 3100mm
  • Roof length: 3000mm
  • Sheet width: 1050mm (16mm Corotherm)

3100 ÷ 1050 = 2.95 → 3 sheets needed

You would order:

  • 3 × 16mm sheets, 1050mm wide, 3000mm long
  • 2 × glazing bars
  • 3 × end closures
  • Breather tape, foil tape and fixing buttons

Example 2 – Larger Carport

  • Roof width: 4200mm
  • Roof length: 4000mm
  • Sheet width: 1050mm (25mm Corotherm)

4200 ÷ 1050 = 4 sheets needed

You would order:

  • 4 × 25mm sheets, 1050mm wide, 4000mm long
  • 3 × glazing bars
  • 4 × end closures
  • Breather tape, foil tape, fixing buttons and flashing tape

Which Polycarbonate Thickness Should I Choose?

As a quick guide:

  • 10mm – Light-duty canopies, smaller lean-tos, budget projects
  • 16mm – Most pergolas, garden covers and open structures
  • 25mm – Enclosed rooms, garden offices, higher insulation

For a pergola or standard garden canopy, 16mm multiwall polycarbonate is normally the best balance of strength, light and cost.

Accessories You’ll Usually Need

For most roofs you’ll also need:

  • Glazing bars – to join and support the sheets
  • Breather tape – for the bottom edges of sheets
  • Aluminium foil tape – for the top edges
  • End closures – to seal and protect the sheet ends
  • Fixing buttons – to secure sheets to rafters
  • Wall flashing tape – where the roof meets a wall

If you’re unsure, contact us and we’ll help you build a complete list for your project.

Need Help with Your Roof Design?

If you’re not confident with measurements or you have an unusual roof shape, we’re happy to help.

We’ll help you choose the right sheet thickness, colour and layout for your project.