Slate Roof Tile Calculator
Slate Roof Tile Calculator
Planning to install or replace a slate roof? This calculator helps estimate how many slate tiles you’ll need based on roof area, tile size, pitch, and headlap. It’s ideal for roofers, DIY renovators, and builders in both the UK and USA.
Technical Guidance
- UK: Standard headlap is 75–100mm; tile coverage depends on gauge and overlap
- USA: Use inches — common headlap is 3–4"; adjust by slope and exposure
- Don't forget dual-pitch roofs — calculate both sides separately
- Include wastage: typically 5–10% for cuts, breakage, and spares
Slate Coverage Table
| Slate Size (mm) | Headlap (mm) | Slates per m² |
|---|---|---|
| 500 x 250 | 100 | 20.4 |
| 600 x 300 | 100 | 13.0 |
| 400 x 250 | 75 | 25.0 |
Pro Tips
- Always confirm roof pitch before choosing tile size and headlap
- Order a few extra bundles to cover future repairs or damage
- Pre-drill slate if cutting to avoid cracking
Common Mistakes
- Forgetting to account for ridge and hip coverage
- Underestimating waste during cutting or transport
- Mixing metric and imperial units (mm vs inches)
FAQs
- How many slates do I need for a 40m² roof? → Depends on tile size. For 500x250mm with 100mm headlap, approx. 816 tiles + waste margin
- Can I use this for dual-pitch roofs? → Yes, just calculate each slope and add them up
- What’s a headlap? → It’s the overlapping part of the slate to prevent water ingress — more overlap = better protection
