The plan
This is the patio for sitting on, not a driveway: 100 mm of compacted MOT Type 1 under it, then a 40 mm sharp sand bedding course, then the slabs. The drawing and the take-off below are for one stated example — a 5 m by 4 m patio, 20.0 m², in 600 × 600 mm slabs with 10 mm joints and 10% for the cuts.
Nothing on this page works anything out. Every quantity comes from the same paving engine the paving calculator runs, so if you change a number the calculator is where you change it; this page shows what it returns and what to do with it.
Plan the space first
Four decisions set everything else. Make them before you buy anything, because changing any one of them changes the whole order — and they are the four inputs the paving calculator asks for.
- How big The area drives every material. A patio that takes a small table and two chairs needs roughly 3 m by 3 m; 5 m by 4 m takes a bigger set with room to walk round it. Measure the space you actually have, and keep the finished level falling away from the house.
- What slab 600 × 600 mm is the common size, and the one used in the example here. A larger slab covers the same area with fewer pieces and fewer joints; a smaller one needs more of both, and more cuts at the edges.
- How wide the joints The joint is added to the slab to make the module the calculator counts, so a wider joint puts fewer slabs in the same run. 10 mm is the usual width for a sawn slab; a riven slab often wants a little more.
- How deep the build-up 100 mm of compacted MOT Type 1 is the figure for a patio you sit on. Anything a car will park on wants more. The bedding is a separate 40 mm sharp sand course on top of the sub-base.
Those four — size, slab, joint width and sub-base depth — are the paving calculator’s own inputs. Enter them there and it returns the slabs, sub-base, bedding sand, jointing and edge restraint in one list you can add to a project.
Doing it, in order
- Decide the four things above first: size, slab, joint width and sub-base depth. Everything after this is those decisions being built.
- Set the patio out with pegs and a line, checking both diagonals are equal so the corners are square, and let it fall away from the house.
- Excavate to the depth of the build-up — the sub-base, the bedding and the slab itself — and decide before you start where the spoil is going.
- Lay and compact the MOT Type 1 in two layers, watering it as you go if it is dusty, until it is firm underfoot.
- Bed the edge restraint on a concrete haunch along the open sides — the sides that meet soil or a step, not the side against the house.
- Screed the sharp sand bedding to a consistent 40 mm, lay the slabs on the module, point the joints, then keep people off it for as long as the maker asks.
Don’t forget
- Jointing sand or paving grout The calculator returns this as “estimate only”: coverage depends on the joint width and the product, so check the maker’s chart rather than trusting a figure here.
- The fall away from the house A patio has to fall away from the building so water does not sit against it. How much depends on the surface and the maker’s guidance, so there is no figure for it on this page.
- Where the spoil goes Excavating for the build-up produces a skip-load of soil and subsoil. Decide before you start where it is going.
- Weed membrane under the sub-base Not always used, and it depends on the ground; on soft or weedy ground a woven membrane under the MOT Type 1 keeps the sub-base clean.
Material take-off for this plan
Worked out by the site’s own Paving for this plan’s dimensions, not typed in by hand.
The working
| Working | Value |
|---|---|
| Paving area | 20.0 m² 5.00 m × 4.00 m |
| Slabs per row | 9 across × 7 down 600 × 600 mm with 10 mm joints |
| Slabs before waste | 63 Plus 10% for cuts and breakages |
| MOT Type 1 sub-base | 3.60 t 20.0 m² × 100 mm × 1.8 t/m³ |
| Sharp sand bedding | 1.28 t 20.0 m² × 40 mm × 1.6 t/m³ |
What to order
| Material | Quantity | Notes |
|---|---|---|
| Paving slabs 600 × 600 mm | 70 slabs | 9 × 7 = 63 plus 10% for cuts. |
| MOT Type 1 sub-base | 3.6 tonnes | ≈ 5 × 850 kg bulk bags at 100 mm compacted. |
| Sharp sand (bedding) | 1.28 tonnes | ≈ 52 × 25 kg bags, or 2 bulk bags, at 40 mm. |
| Edge restraint / kerb and concrete haunch | 18 m | Rule of thumb: the open perimeter, 18.0 m here. An edge that is not restrained lets the paving spread — a kerb on a concrete haunch, or a proprietary edge, is what holds it. Only the edges that meet soil or a drop need it. |
| Jointing sand or paving grout | estimate onlyestimate | Check the manufacturer's coverage for your joint width. |
Sub-base depth is the one number people get wrong. 100 mm compacted is fine for a footpath or light patio; go to 150 mm for anything a car will park on.
A patio project, planned out FAQs
How many slabs do I need for a 5 m by 4 m patio?
70 slabs of 600 × 600 mm with 10 mm joints, from the paving calculator. The grid takes 63 — 9 across by 7 down — and the order is 70 once the 10% cutting allowance is added.
How much sub-base does a 5 m by 4 m patio need?
3.60 tonnes of MOT Type 1 at 100 mm compacted, which is about five 850 kg bulk bags. That is the figure the paving calculator returns for 20.0 m² at that depth.
How much sharp sand goes under the slabs?
1.28 tonnes at a 40 mm bedding depth, which is about 52 bags of 25 kg or two bulk bags. Bedding between 30 mm and 50 mm is the usual range.
Is 100 mm of sub-base enough for a patio?
For a patio you sit on, yes. Go to 150 mm for anything a car will park on — the paving calculator takes the depth as an input, so you can see what the heavier figure costs.
Does this page calculate the patio itself?
No. It hands off to the paving calculator: change the size, the slab, the joint width or the depths there and it returns an updated list you can add to your project.