Roofing Calculator
Estimate your roof area, required tiles, and underlayment quantities accurately. Includes pitch adjustments and waste factors for your UK roofing project.
Calculate Your Roofing Materials
Enter your roof dimensions and material preferences to instantly see the total surface area, required tiles, and underlayment needed.
Roofing Estimator Tool
Calculate area and material quantities with precision.
How it Works
Understanding roofing calculations
Measure the Footprint
We start by calculating the flat, horizontal area of your roof by multiplying the length by the width.
Apply Pitch Factor
Roofs are sloped, meaning the actual surface area is larger than the footprint. We multiply by a pitch factor to find the true sloped area.
Add Waste Allowance
Cutting tiles around chimneys, valleys, and edges creates waste. We add your specified waste percentage to ensure you order enough materials.
Calculate Quantities
Using the final adjusted area and your chosen tiles per square metre, we calculate the total number of tiles and underlayment required.
Material Coverage
General guidelines for how many roofing units are typically required per square metre in the UK.
| Material Type | Units per m² (Approx.) | Recommended Min. Pitch |
|---|---|---|
| Concrete Interlocking Tiles | 10 | 15° – 22.5° (depending on profile) |
| Clay Plain Tiles | 13 | 35° (can be lowered to 25° with underlay) |
| Natural Slate (500x250mm) | 25 – 29 | 20° – 25° (depending on lap) |
| Artificial / Fibre Cement Slate | 15 – 18 | 15° – 20° |
| Standing Seam Metal | 1 (per sheet) | As low as 3° (with appropriate system) |
| Flat Roof Membrane (EPDM/GRP) | 1 (per m²) | 1° – 2° (for drainage fall) |
Roofing Calculation FAQ
Answers to the most frequently asked questions about measuring roofs and estimating materials in the UK.
To calculate your roof area, measure the length and width of the roof plane to get the flat footprint area. Then, multiply this by a pitch factor (e.g., 1.15 for a 30-degree pitch) to account for the slope. Finally, add a waste factor (typically 10-15%) for cuts and breakages.
A roof pitch factor is a multiplier used to convert the flat footprint area of a roof into the actual sloped surface area. For example, a flat roof has a factor of 1.0, a 30-degree pitch is approximately 1.15, and a 45-degree pitch is 1.41.
This depends on the tile type and the roof pitch. As a general guide: concrete tiles require about 10 tiles per m², clay tiles require around 13 tiles per m², and natural slate can require 25 to 30+ tiles per m² depending on the slate size and lap.
For a simple, rectangular roof, a 10% waste factor is usually sufficient. For complex roofs with multiple valleys, hips, dormers, or chimneys, it is recommended to add 15% to 20% to account for increased cutting and breakages.