DIY & materials · Calculator companion · By K Imports
Roof tiles and slates: practical guide
This guide explains how to use the Count.ie roof tiles and slates. Convert horizontal roof area to pitched covering and ridge units. Follow the inputs, method and worked example below, then compare your own scenario.
Guide written .
Open the Roof tiles and slates calculatorWhat to prepare
- Measure the actual space and record every dimension with its unit.
- Check the supplier's pack size, stated coverage and installation instructions.
- Separate the measured requirement from waste, cuts, overlaps and spare material.
Understand the inputs
The calculation method
Pitched area = horizontal area ÷ cos(pitch). Covering uses manufacturer units/m²; ridge units use effective covered length.
Worked example
Illustrative inputs and their result.
Example inputs
- Horizontal roof plan area (m²)
- 80
- Roof pitch (degrees)
- 30
- Manufacturer covering units per m²
- 10
- Waste allowance (%)
- 10
- Covering price per unit (€)
- 2
- Ridge length (m)
- 10
- Effective ridge unit length (m)
- 0.45
Calculated example result
- Covering Units
- 1,017
- Roof Area M2
- 92.38 m²
How to interpret the result
The calculated quantity is a planning estimate, not an installation specification. Whole packs and site conditions can change the order; structural or safety-critical work needs appropriate professional guidance.
Compare alternative dimensions or pack sizes without changing the unit basis. Re-measure uncertain areas before buying, and use the manufacturer's instructions to decide a suitable allowance.
Common mistakes to avoid
- Convert millimetres, centimetres and metres before combining measurements.
- Do not add the same waste allowance at both measurement and ordering stages.
- Check irregular shapes, openings, substrate conditions and manufacturer coverage separately.
Assumptions and sources
Uniform roof pitch estimate. Manufacturer headlaps and exposure determine coverage; roof fixings, ventilation and structural design are excluded.
If your case falls outside this scope, use a more suitable calculator or contact us about an unclear method.