Calculating the number of slates needed for your roof project can seem tricky, but this guide will have you sorted in no time.

With a few key details about your slate size and roof pitch, you’ll be able to estimate the slate coverage and materials required.

## How Many Roof Slates Per M2?

The number of roof slates needed for effective coverage depends on the size of the slate and the lap in millimetres.

The most common values are as follows:

– 400mm x 200mm: approximately 31 slates per square metre

– 400mm x 250mm: approximately 25 slates per square metre

– 500mm x 250mm: approximately 19 slates per square metre

## Key Points

– Slate roof coverage is 14-31 slates per m2 depending on slate size

– Cost per m2 is £160-£210 for slate roofing

– Proper installation is key for longevity

## Our Opinion

As slate roofing experts, we recommend selecting a durable slate size that balances aesthetics and affordability.

Aim for at least 14 slates per square metre coverage with proper overlaps.

Investing in a quality slate roof with proper installation will pay off for decades through beauty and protection.

## How Many Slates per Square Metre?

The number of slates needed per square metre depends on the size of the slates and the headlap (overlap between courses). Here are some typical values:

- 400 x 200 mm slates – approximately 31 per m2
- 400 x 250 mm slates – approximately 25 per m2
- 500 x 250 mm slates – approximately 19 per m2

An easy way to calculate the exact number is by using a **roof slate calculator**. Simply enter the slate size and headlap, and it will provide the coverage rate.

For example, 270 x 180 mm slates with a 100mm headlap need approximately 64 slates per m2.

Note that BS5534 provides minimum slate pitch and headlap guidance. Improved fixing techniques from suppliers like Easy Slate allow for greater flexibility.

In summary, you’ll need approximately 25 slates per m2 for a typical roof slate project. With the right slate calculator, you can calculate the exact number needed based on your slate size and roof specifics. This helps minimise wastage and ensures you order the right quantities.

## Calculate Slates Needed For Roof

Once you know the number of slates per square metre, it’s simple to estimate the total slates needed.

Start by measuring the total roof area in square metres. This includes the main roof and any dormers or valleys. For a simple rectangular roof, it’s just length x width.

Next, multiply this area by the number of slates per square metre from your calculator. This gives the total number of slates required.

For example, say your roof area is 35 m2, and you’ll be using 400×200 mm slates at 31 per m2. That’s 31 slates x 35 m2 = 1,085 slates needed in total.

Remember to add 5-10% extra for breakages, cutting, and wastage. It’s better to have a few spares than to run short halfway through the job.

When ordering, also consider slate colour blending. Mixing slates from different pallets can help avoid colour banding on the roof. Your supplier can advise on requirements.

With the slate quantity estimated, you can get an accurate price for budgeting. Remember to account for additional materials like underlay, fixings, ridge tiles and ventilation.

In summary, measure your roof area, multiply by slates per m2, add wastage, and you’ve got the number of slates required. A professional roofer can also calculate requirements if you need extra peace of mind.

## Slate Sizes and Coverage

When estimating slates needed, the size of slate you choose affects how many are required per square metre.

Standard slate sizes in the UK are usually between 300-600 mm long and 150-250 mm wide. The most common are 400×200 mm and 500×250 mm.

As a rule of thumb, larger slates need fewer per m2 for full coverage. Smaller slates need more.

For example, 400×200 mm slates require approximately 31 per m2, while 600x300mm slates need approximately 22 per m2.

To calculate exactly, divide 1m2 (1,000 mm x 1,000 mm) by the slate width to get several slates per row. Then divide 1,000 mm by slate length to get rows per m2. Multiply these together to find slates per m2.

So for 500×250 mm: 1,000 mm / 250 mm = 4 slates per row. And 1,000 mm / 500 mm = 2 rows per m2. So 4 slates x 2 rows = 8 slates per m2.

Remember though that real roofs involve cutting and wastage. It’s best to add 5-10% extra when ordering.

Consider colour blending too. Mixing slate sizes can sometimes improve appearance by breaking up banding.

In summary, larger slates need fewer per m2 but allow for wastage. Calculate exact quantities based on size to estimate roof slate requirements.

## Factors Affecting Slates per M2

While slate size is the main factor, a few other things can influence the quantities needed:

**Overlap**– The overlap between slates affects coverage. The standard is approximately 32-35 mm. A larger overlap means fewer slates per m2.**Gauge**– This refers to the exposure of each slate. A larger gauge (less exposed) uses more slates per m2.**Pattern**– Simple regular patterns are most efficient. Complex or staggered patterns use more slate.**Wastage**– As mentioned, allow 5-10% extra for cutting and breakages.**Roof Shape**– Complex roofs with valleys, hips and irregular edges need more cutting and custom work.**Mixing Sizes**– Blending different slate sizes impacts quantities and calculations.

Consider all these factors when estimating the total roof slates needed using the slates per m2 calculation. Experienced roofers can advise on adjustments based on your specific roof.

With some simple slate measurements and calculations, you can get a good idea of slate quantities needed for your roofing project.

## Estimating Slates for Your Roof

When estimating slates needed for a roofing project, start with a few key measurements:

- Area of the roof in m2. For simple rectangles, multiply length by width. For more complex shapes, break it into sections.
- Slate size – length, width and headlap coverage.
- Standard overlaps and gauges for your slate type and roof pitch.

With this information, you can calculate the number of slates per m2 based on the slate dimensions and overlaps. Then multiply this by the total roof area for an estimate of slates needed.

Don’t forget wastage – add 5-10% to allow for cutting, shaping and breakages. It’s better to have a few extra than run short halfway through the job.

For accuracy, have an experienced roofer assess the roof and advise on adjustments for shape, valleys, edges and other factors. Their expertise can refine your DIY calculations.

Estimating slate quantities takes a bit of measuring and maths, but gives a solid starting point. With the roof area and slates per m2 figure, you can budget and order slates with confidence.

## FAQ

### How many slates are in a m2?

Approximately 14-31 slates per square metre depending on slate size.

### How many slates should a roofer lay in a day?

An experienced roofer can lay approximately 20-30 square metres of slate per day.

### How many slate tiles are on an average roof?

The number of slates needed for an average-sized roof is usually between 1000-2000.

### How many slates per m2 for fibre cement?

Fibre cement slates require approximately 30-40 slates per square metre.

## Conclusion

In summary, you will need between 14-31 slates per square metre for a slate roof, with costs ranging from £160 to £210 per square metre. Proper slate selection, layout and installation are key for an attractive and durable slate roof.