Roofing Calculator

How to use the Roofing Calculator

1. Enter the roof dimensions — plan area and pitch angle.
2. Select the tile or slate type and size from the dropdown.
3. Add any hip or valley lengths if the roof is not a simple gable.
4. Review the quantities for tiles, battens, felt, ridge tiles, and fixings.

Why use this tool

• Converts a flat plan area into the true sloped area using trigonometry, so you order the right amount.
• Includes batten gauge and felt coverage calculations that are easy to forget when estimating.
• Gives a materials list you can hand straight to your merchant for pricing.

Roof area estimation trips up even experienced builders because the plan area drawn on paper is always smaller than the actual sloped surface. A 45-degree pitch increases the true area by over 40%. This calculator applies the correct pitch multiplier and then works out tile quantities based on standard gauge and lap dimensions. Batten spacing, felt rolls, and ridge fittings are all included. Always add a waste allowance for cuts around hips, valleys, and abutments — 10% is a reasonable starting point for a straightforward roof. Check the selected product's declared cover width, minimum pitch, headlap and fixing specification before ordering because profiles vary between manufacturers. Measure each roof plane separately on extensions, dormers and intersecting roofs, then add leadwork, ventilation, dry-fix components, access equipment and disposal as separate quote lines.

Part of Builder Tools Calculators — free construction tools for UK tradespeople.