Patio Pattern Generator
A slab count that includes the cuts, and a layout drawn to scale.
What this tool does
Enter the patio dimensions, pick a slab size and a laying pattern, and it counts whole slabs and edge cuts separately, then adds a wastage allowance. That total is higher than area divided by slab size, because the usual sum assumes every offcut gets reused and offcuts almost never fit anywhere.
Counts whole slabs and edge cuts separately for a given patio size and laying pattern.
Draws the layout to scale, marking which slabs need cutting.
How to use it
- Enter the patio width and length in metres.
- Choose a slab size and a laying pattern.
- Set the joint width - 10mm is usual for slabs.
- Read the order figure, and check the drawing for a bad fit before you buy.
- Tap a size chip for a common patio, then adjust from there.
- Enter a price per slab to cost the order, and watch the bar for how much of the job is cutting.
Why use this generator
Paving costs depend on whole slabs and the cuts at the edges, and under-ordering is common. A slab count with cuts separated, and a scaled layout, helps ordering and planning.
Why we built it
We built the patio pattern generator to count whole slabs and edge cuts separately, rather than dividing area by slab area. Order the base with the gravel calculator and the bedding with the concrete calculator.
For a neighbouring job there is also the Crochet Pattern Maker and the Knitting Row Counter.
Who this tool is for
- Homeowners laying a patio
- Landscapers pricing paving
- Designers planning a layout
When to use it
- Planning a patio or path.
- Ordering slabs with an allowance for cuts.
- Comparing laying patterns.
- Showing a layout to a contractor.
Why the count is higher than you expected
The usual sum under-orders.
Because dividing the area by the slab size is the wrong sum. It assumes every offcut from a cut slab gets used somewhere else on the patio, and offcuts almost never fit anywhere - you cut a slab to fill a 200mm strip and the remaining 400mm goes in the skip. This counts whole slabs and cut slabs separately, so the total reflects what you actually lay rather than what the area theoretically absorbs.
The tool shows both figures side by side, so you can see the size of the difference rather than take a number on trust.
The pattern changes the count
Not just how it looks.
A stack bond on a patio whose dimensions divide evenly needs no cuts at all. The same area in stretcher bond needs a part-slab at both ends of every offset course. In herringbone, the units run diagonally into every boundary, so the whole perimeter is cut.
That is a real difference in what you order, and no competing calculator asks which pattern you are laying.
Which patterns need a rectangular slab
Two of the four.
Herringbone and basketweave. Both work by units interlocking, which only happens when the slab is exactly twice as long as it is wide - 600x300, for instance. On a square slab neither pattern exists, so this refuses to draw them rather than producing a picture of something that cannot be built. Stack bond and stretcher bond work with any size.
The standard sizes
Seven of them, lettered.
The British Standard precast concrete flag comes in seven sizes, designated A to G: 600x450 (A), 600x600 (B), 750x600 (C), 900x600 (D), 450x450 (E), 400x400 (F) and 300x300 (G). The three most commonly stocked by builders’ merchants are 900x600, 750x600 and 600x600, all at 50mm thick. 63mm and 70mm units exist for anywhere a vehicle will drive over. 600x300 is not a BS flag but is the commonest modern rectangular paver, so it is offered too.
What you give it, and what you get back
| Item | Details |
|---|---|
| Input | Patio dimensions, slab size and pattern. |
| Output | Whole slabs, cut slabs and a scaled layout. |
| Notes | Allowances for herringbone and basketweave. |
Issues you may run into
| What you see | Why it happens | What to do |
|---|---|---|
| Shape is not rectangular | Only rectangles are supported. | Split into rectangles and add results. |
| Cut counts differ on site | Allowances are estimates. | Order extra slabs. |
| Joint width ignored | Gaps are small. | Add a margin for spacing. |
Assumptions and limitations
- Rectangular patios only. An L-shape or a curve needs splitting into rectangles and adding the results, and a curved edge cuts far more than a straight one.
- The cut counts for herringbone and basketweave are an allowance based on the perimeter, not a slab-by-slab diagonal solve. They are deliberately generous rather than optimistic.
- It does not estimate sub-base, sand or mortar. Those depend on ground conditions and intended use, which a layout cannot know.
Frequently asked questions
How many paving slabs do I need?
Enter your dimensions and pattern above. The short version: more than area divided by slab size, because the edges have to be cut and the offcuts rarely fit anywhere else.
Why is this number higher than other calculators?
Because dividing the area by the slab size is the wrong sum. It assumes every offcut from a cut slab gets used somewhere else on the patio, and offcuts almost never fit anywhere - you cut a slab to fill a 200mm strip and the remaining 400mm goes in the skip. This counts whole slabs and cut slabs separately, so the total reflects what you actually lay rather than what the area theoretically absorbs.
What are the standard UK paving slab sizes?
The British Standard precast concrete flag comes in seven sizes, designated A to G: 600x450 (A), 600x600 (B), 750x600 (C), 900x600 (D), 450x450 (E), 400x400 (F) and 300x300 (G). The three most commonly stocked by builders’ merchants are 900x600, 750x600 and 600x600, all at 50mm thick. 63mm and 70mm units exist for anywhere a vehicle will drive over. 600x300 is not a BS flag but is the commonest modern rectangular paver, so it is offered too.
Which patterns need a rectangular slab?
Herringbone and basketweave. Both work by units interlocking, which only happens when the slab is exactly twice as long as it is wide - 600x300, for instance. On a square slab neither pattern exists, so this refuses to draw them rather than producing a picture of something that cannot be built. Stack bond and stretcher bond work with any size.
How much wastage should I allow?
10% is the usual allowance for breakage, bad cuts and the occasional damaged slab in a pack. Go to 15% for a complex shape, a lot of curves, or a natural stone with variable quality.
What joint width should I use?
10mm is typical for slabs, and the tool defaults to it. The joint is added to each slab’s footprint rather than taken off the area, because a 600mm slab with a 10mm joint occupies 610mm of run - over a long patio, ignoring that is a whole extra course.
Sources and accuracy
pavingexpert.com — British Standard precast concrete flag sizes A-G
Figures last checked against the source on . Standards and rates can change — if you are relying on this for something that matters, confirm against the source above. Think a figure is wrong or out of date? Send a correction.
Further reading
How many paving slabs do I need? The maths calculators get wrong — Dividing patio area by slab size under-orders, because offcuts rarely fit. Here is the calculation that counts whole slabs and cut pieces separately.