online slate calculator

Slates per m2

Calculate how many slates you will need per m2 based upon, size, type and required headlap. Remember, always factor in slate and a half and a percentage for cuts and waste. Learn more about roof slates using our handy guides.

Roof Slate Calculator

how many roof slates per m2

Slating Headlap

Lap

Please choose Headlap50mm75mm100mm

Choosing Headlap

Definition: The vertical overlap between successive rows of tiles to prevent water ingress.

Factors to consider:

• Roof pitch: Shallower pitches (< 30°) need 75–100 mm; steeper (> 45°) can use 50 mm.
• Climate & exposure: Wind-driven rain or heavy rainfall zones benefit from more headlap.
• Tile profile: Deeper tiles may require extra overlap to seal correctly.

Rule of thumb:

• Standard (30–45°): 50–75 mm
• Low (< 30°): 75–100 mm
• High (> 45°): 50 mm

Slate Size / Type

Slate 50mm Lap

Please choose slate size24x14 (610mmx355mm) Princess24x12 (610mmx305mm) Duchess22x12 (560mmx280mm) Small Duchess22x11 (560mmx280mm) Marchioness20x12 (510mmx305mm) Wide Countress20x10 (510mmx255mm) Countess20x9 (510mm x 230mm) Countess18x12 (460mm x305mm) Countess18x10 (460mm x 255mm) Wide Viscountesses18x9 (460mm x 230mm) Viscountesses16x12 (405mm x 305mm) Viscountesses16x10 (405mm x 255mm) Wide Ladies16x9 (405mm x 230mm) Broad Ladies16x8 (405mm x 205mm) Ladies14x10 (355mm x 255mm) Headers14x8 (355mm x 205mm)14x7 (355mm x 180mm)13x10 (330mm x 255mm)13x7 (330mm x 180mm) Doubles12x10 (305mm x 255mm) Doubles12x8 (305mm x 205mm) Wide Doubles12x6 (

Selecting Tile Size

Coverage per tile: Larger tiles cover more area but are heavier, affecting handling and substrate load.

Aesthetic scale: Big tiles suit modern, minimal lines on large roofs; smaller tiles give more texture and a traditional look.

Structural limits: Check rafters and battens can support the chosen tile’s weight and fixing centres.

Installation speed vs. waste: Larger tiles lay faster but may require more cutting at edges, increasing waste. Smaller tiles take longer but can reduce off-cuts.

Compatibility: Ensure the tile size works with your chosen headlap & side-lap for correct coverage per m².

By balancing pitch, weather, substrate capacity and appearance, you’ll pick the optimal tile size for performance and style.

Slate 75mm Lap

Please choose slate size24x14 (610mmx355mm) Princess24x12 (610mmx305mm) Duchess22x12 (560mmx280mm) Small Duchess22x11 (560mmx280mm) Marchioness20x12 (510mmx305mm) Wide Countress20x10 (510mmx255mm) Countess20x9 (510mm x 230mm) Countess18x12 (460mm x305mm) Countess18x10 (460mm x 255mm) Wide Viscountesses18x9 (460mm x 230mm) Viscountesses16x12 (405mm x 305mm) Viscountesses16x10 (405mm x 255mm) Wide Ladies16x9 (405mm x 230mm) Broad Ladies16x8 (405mm x 205mm) Ladies14x10 (355mm x 255mm) Headers14x8 (355mm x 205mm)14x7 (355mm x 180mm)13x10 (330mm x 255mm)13x7 (330mm x 180mm) Doubles12x10 (305mm x 255mm) Doubles12x8 (305mm x 205mm) Wide Doubles12x6 (

Selecting Tile Size

Coverage per tile: Larger tiles cover more area but are heavier, affecting handling and substrate load.

Aesthetic scale: Big tiles suit modern, minimal lines on large roofs; smaller tiles give more texture and a traditional look.

Structural limits: Check rafters and battens can support the chosen tile’s weight and fixing centres.

Installation speed vs. waste: Larger tiles lay faster but may require more cutting at edges, increasing waste. Smaller tiles take longer but can reduce off-cuts.

Compatibility: Ensure the tile size works with your chosen headlap & side-lap for correct coverage per m².

By balancing pitch, weather, substrate capacity and appearance, you’ll pick the optimal tile size for performance and style.

Slate 100mm Lap

Please choose slate size24x14 (610mmx355mm) Princess24x12 (610mmx305mm) Duchess22x12 (560mmx280mm) Small Duchess22x11 (560mmx280mm) Marchioness20x12 (510mmx305mm) Wide Countress20x10 (510mmx255mm) Countess20x9 (510mm x 230mm) Countess18x12 (460mm x305mm) Countess18x10 (460mm x 255mm) Wide Viscountesses18x9 (460mm x 230mm) Viscountesses16x12 (405mm x 305mm) Viscountesses16x10 (405mm x 255mm) Wide Ladies16x9 (405mm x 230mm) Broad Ladies16x8 (405mm x 205mm) Ladies14x10 (355mm x 255mm) Headers14x8 (355mm x 205mm)14x7 (355mm x 180mm)13x10 (330mm x 255mm)13x7 (330mm x 180mm) Doubles12x10 (305mm x 255mm) Doubles12x8 (305mm x 205mm) Wide Doubles12x6 (

Selecting Tile Size

Coverage per tile: Larger tiles cover more area but are heavier, affecting handling and substrate load.

Aesthetic scale: Big tiles suit modern, minimal lines on large roofs; smaller tiles give more texture and a traditional look.

Structural limits: Check rafters and battens can support the chosen tile’s weight and fixing centres.

Installation speed vs. waste: Larger tiles lay faster but may require more cutting at edges, increasing waste. Smaller tiles take longer but can reduce off-cuts.

Compatibility: Ensure the tile size works with your chosen headlap & side-lap for correct coverage per m².

By balancing pitch, weather, substrate capacity and appearance, you’ll pick the optimal tile size for performance and style.

Slates Per m2

Calculating Slates per m²

Definition: Number of slates needed to cover one square metre.

Formula: 1 000 000 mm² ÷ (effective width × effective height)

Where:

• Effective width = tile width – side lap
• Effective height = tile height – head lap

Example: 610 mm × 355 mm tile, 20 mm side lap, 75 mm head lap:

• Effective width: 610 − 20 = 590 mm
• Effective height: 355 − 75 = 280 mm
• Area per slate: 590 × 280 = 165 200 mm²
• Slates per m²: 1 000 000 ÷ 165 200 ≈ 6.05

Adjust your headlap and sidelap values for precise coverage calculations.

Slate Required(Required)

Choose a slate typePenrhynCwt-y-BugailWestmorland Green SlateVillar Del Rey SlateLousaval Dark SlateFerlosa Spanish SlateVermont Natural Green SlateSumo SlateBrazilian Roof Slate

Measure Your Roof Area

Determining Your Roof’s Area (m²) Accurately measuring your roof is essential to estimate how much slate you’ll need. Follow these steps: Measure the rafter length Runs from the gutter up to the ridge line.

Width (m)

Length (m)

Total Mtr²

Total Slates Required

Total Slates Required

Total Slates Required

Copper Nails Total KG

Copper Nails for Slating: Overview & Specs

Why use copper nails?

• Corrosion resistance: Forms a protective patina to prevent rust and staining.
• Superior durability: Lasts for decades without needing replacement.
• Optimal flexibility: Absorbs roof movement without cracking or shearing.
• Aesthetic harmony: Weathers to a warm patina that complements natural slate.
• Chemical compatibility: No galvanic reaction with slate or lead flashings.

Packaging & usage:

• Approx. 250 copper nails per kg
• Minimum 2 nails per slate
• Recommended length: 25–30 mm shank, 3.35 mm (4 gauge) head

Get a Free Quote

We’ll find the best price for the slates you need and email you a no-obligation quote.

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How many slates per m2?

Welcome to Reclaimed Slate: Your Ultimate Roofing Slate Calculator
At The Reclaimed Company ®, we understand that every roofing project is unique. Whether you’re a homeowner looking to renovate your roof or a roofing contractor planning a commercial roofing project, our goal is to provide you with the tools and resources you need to make informed decisions.

Why Choose The Reclaimed Company?

Accuracy: Our advanced roofing slate calculator takes into account various factors such as roof dimensions, slate size, pitch, and waste, ensuring precise estimations tailored to your project requirements.

Efficiency: Say goodbye to manual calculations and guesswork. With The Reclaimed Company, you can quickly generate detailed estimates, saving you time and effort.

Versatility: Whether you’re working on a simple residential roof or a complex commercial structure, our calculator adapts to suit your needs, providing flexibility and reliability.

How to Use the Roofing Slate Calculator
Using our roofing slate calculator is easy. Simply input the required information such as roof dimensions, desired slate size, and pitch, and let us do the rest. Within seconds, you’ll receive accurate estimates for the quantity of slates needed, along with waste calculations to minimise material costs. Remember to factor in slate and a half into your calculations and consider the typs of fixings required. 

Fixings for slates

When it comes to slate roofing, you will need to comply with BS5534. The fixings needed are specific and consist of copper nails with a gauge of at least 3.35mm.

Learn more about BS5534 here, and make sure you quantify the number of nails that you need correctly.

For reference, there are 250 copper nails per kg, which is sufficient to fix 125 number slates assuming two fixings per slate. Therefore, to fix 1000 roof slates, you will need 5Kg of copper nails. 

Our Commitment to Quality

At The Reclaimed Company, we prioritise quality and customer satisfaction above all else. That’s why we partner with leading slate manufacturers known for their superior products. Whether you prefer traditional Welsh slate or modern alternatives, we’ve got you covered.

Get Started Today!
Ready to take the guesswork out of your roofing project? Try our roofing slate calculator now and experience the difference The Reclaimed Company can make. For additional assistance or inquiries, don’t hesitate to contact our friendly team. We’re here to help you achieve roofing excellence every step of the way.

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