Slate roof calculator
Slate piece counts depend on slate size and exposure, so we ask you to enter the coverage rather than guess it.
Why it's user-input
Slate comes in many sizes, and the exposure (the amount of each slate left visible) is set by the slate length and the roof pitch. There is no single safe pieces-per-square default — a guessed number would simply mislead you, so the calculator asks for your figure.
Where to find your figure
Your slate supplier publishes pieces per square for each size and exposure combination. Enter that number in the calculator and it handles the area, waste, and total for you.
Suitable pitches
Slate needs a steep roof — at least 4:12, and steeper is better for a material that sheds rather than seals. It is never a low-slope option.
Weight and structure
Slate is among the heaviest roofing materials. Roofs carrying slate are usually engineered for it; adding slate to a structure not designed for the load is a job for an engineer, not a calculator.
Lifespan and cost
Genuine slate can last a century or more — the longest-lived common roofing material — which is the case for its high material and labor cost. We publish no pricing; use your own rate.
Trade-offs
Unmatched longevity and appearance against very high cost, heavy weight, brittleness, specialist installation, and a steep-slope requirement.