Free tool · BuildMeA Projects
Roof Tile & Slate Calculator
Ordering roof coverings by eye is how you end up short a pallet on day two, or paying to send tiles back. Enter your roof area — or the plan size and pitch — pick your tile or slate, and get an honest count with battens, membrane and ridge tiles to match.
Ridge / hip tiles: —
Every figure here is an ESTIMATE and rounded up. Real quantities depend on the exact product, pitch, laps, cuts and detailing — always confirm against the manufacturer's fixing data and keep a few spares for breakages.
How many roof tiles per square metre?
It depends on the covering. Large interlocking concrete tiles need roughly 10 per m², natural and fibre-cement slates around 20 per m² (for a common 500×250mm slate at standard gauge), and small plain clay or concrete tiles about 60 per m² because they are double-lapped. Always check the exact figure on the manufacturer's data sheet — it changes with the tile size and the batten gauge you set out — then adjust the per-m² field to match.
How do I work out my roof area?
Measure the flat footprint on the ground first — length along the ridge by the width from eaves to eaves — to get the plan area. Because the roof slopes, its actual surface is larger, so multiply the plan area by a pitch factor of 1 ÷ cos(pitch). A 30° roof has a factor of about 1.15, 45° about 1.41. This tool does that for you: enter the plan size and pick the pitch, or switch to slope-area mode and type the figure straight in if you have already measured up the roof.
How much roofing membrane do I need?
Take your slope area and add roughly 15% for the horizontal and vertical overlaps between rolls, which is why this calculator multiplies the slope area by 1.15. Breathable underlay is usually sold in rolls of a set width and length, so round the membrane figure up to whole rolls and allow extra where you have hips, valleys or a complicated eaves detail. Battens are estimated as slope area divided by the gauge, giving the linear metres of batten to order.
Does this tool store my details?
No. There is no sign-up and nothing to submit — every calculation runs entirely in your browser as you type. Nothing you enter is uploaded, saved or sent anywhere, so you can use it as many times as you like without leaving a trace.
Please note: this tool gives a guide or estimate only. It may not be 100% accurate and is not professional advice — always check the figures before you rely on them. Nothing you enter is uploaded — the calculation runs entirely in your browser.
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