LoadingLoadingLoadingLoadingPick a slate size or enter your own, set the headlap, and get the batten gauge, slates per square metre, the order quantity and an indicative delivery weight for the scaffold and the wagon.
Free to use · Runs entirely in your browser · No signup required
100 mm headlap suits most UK roofs at 30° and above; increase it for lower pitches and exposed sites. 500 × 250 mm at a 100 mm lap works out at 20 slates per m² — the classic figure.
Batten gauge
200 mm
(Slate length − headlap) ÷ 2 — the spacing between batten centres.
Slates per m²
20.0
Slates to order
1,260
Delivery weight
2.17 t
Order quantity × weight per slate at 2,750 kg/m³ nominal density — natural slate varies by quarry.
Roof load
34 kg/m²
Waste depends on the roof. A simple gable with square verges can come in around 5%; hips, valleys and heavy cutting push it to 7.5–10%. Natural slate also breaks in transit and in handling more readily than concrete tile, so allow for the site as well as the shape.
Confirm headlap, gauge, minimum pitch and the fixing specification against the manufacturer's or supplier's data for the slate you're using. Headlap increases with lower pitches and greater exposure, and that changes the count.
An ordering and loading estimate. It is not a structural assessment, a manufacturer specification or a substitute for an on-site survey.
Turn this materials estimate into a roofing quote in Cushty — line items, VAT and a document you can send.
See how quoting worksSlate is laid double-lapped: every slate overlaps the course two below it, so each part of the roof is covered by two thicknesses. That is what sets the batten gauge — the spacing between battens — at half the exposed length once the headlap is taken off. Gauge and slate width together give the slates per square metre, and everything else follows from that.
Gauge = (slate length − headlap) ÷ 2 Slates per m² = 1,000,000 ÷ (gauge × width) To order = ⌈⌈area × per m²⌉ × (1 + waste %)⌉
Lengths in millimetres. Increasing the headlap reduces the gauge, which increases the slates per square metre — more lap always means more slate.
A 60 m² roof in 500 × 250 mm slate at 100 mm headlap.
1,260 slates. At 5 mm thick that is roughly 1.72 kg each and about 34 kg per square metre of roof — worth knowing before anyone assumes the existing structure will take it.
The other roofing calculators cover the steps either side of this one.
Slating is double-lap: every part of the roof carries at least two thicknesses of slate, and the batten gauge — (length − headlap) ÷ 2 — sets how many you need. Get the lap wrong and the count is wrong across the whole roof.
Weight matters as much as count. Natural slate runs around 25–35 kg per square metre on the roof, and several tonnes arrive on the wagon for an average re-roof. The structure, the scaffold loading bay and the delivery plan all need that number before the slates do.
Calculators and generators we built for UK service businesses. All free, all in-browser, no signup.
Book a 30-minute walkthrough — we'll show you how Cushty fits your business. No commitment, no contract until you choose to subscribe.
UK-hosted · GDPR compliant · Month to month · Cancel any time
