Patio Size & Paving Calculator
Planning a new patio means knowing how many slabs to order and roughly what the materials will cost before you commit — get it wrong and you're either short on slabs mid-build or left with an expensive pile of leftovers. Enter your patio's length and width along with your chosen slab size below, and we'll calculate the number of slabs needed, with a sensible allowance for cutting, plus a rough UK cost range so you can budget with confidence.
Enter your patio dimensions
We'll work out how many slabs you need, plus a cutting allowance.
Enter a length and width above to see how many slabs you'll need.
Recommended for your patio
Garden furniture to make the most of your new outdoor space.
- Rattan
- Patio dining
Currently unavailable
Pros
- All-weather PE rattan weave
- Rising table with built-in ice bucket
- Showerproof, UKFR-compliant cushions
Cons
- Heavy — needs two people to move
- Premium price for the corner + footstools configuration
- Rattan
- Balconies & small patios
£299.99
Pros
- Compact — fits small patios and balconies
- Removable, machine-washable cushion covers
- Glass-top coffee table with storage shelf
Cons
- Cushions fade after a season in direct sun
- Resin
- Balconies & small patios
£170.00
Pros
- Fully weatherproof resin, rattan-effect weave
- Built-in storage table doubles as a coffee table
- Compact size ideal for balconies
Cons
- Seats two only
- No cushions included as standard
Frequently asked questions
Do I need planning permission for a patio?
Most garden patios count as permitted development and don’t need planning permission, provided the patio (combined with any other hard surfacing) doesn’t take the total covered area of the garden over 50%. If your patio will raise the ground level significantly, sit close to a boundary, or your property has restrictive covenants or is a listed building, it’s worth checking with your local council first.
How thick should patio slabs be?
For a standard domestic patio taking foot traffic and garden furniture, 35-40mm concrete slabs are typical. If the patio will need to support a driveway, hot tub, or heavier loads, look for thicker slabs (50mm+) or ones specifically rated for vehicular use.
What base do I need under paving?
A typical patio build is a compacted sub-base of MOT Type 1 hardcore (75-100mm), topped with a bed of sharp sand and cement mortar (or a semi-dry mortar mix) that the slabs are laid on. Good drainage and a slight fall away from the house (roughly 1:80) are essential to stop water pooling or running into your home.
How much extra should I order for cutting and wastage?
We build in a 10% allowance on top of the raw number of slabs needed to cover your patio area, which typically covers cuts around edges, borders, and any breakages during laying. Irregular patio shapes or intricate patterns may need a slightly higher allowance.
How this calculator works
The calculator multiplies your patio length by width to get the total area in square metres, then divides that by the area of one slab to find the base number of slabs required. It then adds a 10% wastage allowance on top to cover cutting losses around edges, breakages during handling, and any mistakes while laying. The final figure is rounded up to the nearest whole slab, since you can’t buy part of a slab.
The tool also shows a rough materials cost range based on three UK price bands: budget concrete or riven slabs, mid-range textured concrete or basic natural stone, and premium Indian sandstone, porcelain or granite. These are supply-only prices per square metre — they don’t include base preparation, sand, mortar, jointing compound or labour, all of which can add significantly to the final bill.
UK patio slab sizes
| Slab size | Area per slab | Slabs per 10m² | Typical use |
|---|---|---|---|
| 400 x 400mm | 0.16m² | ~63 | Small patios, footpaths, borders |
| 450 x 450mm | 0.20m² | ~50 | Small-to-medium patios, general use |
| 600 x 600mm | 0.36m² | ~28 | Medium patios, modern look |
| 600 x 900mm | 0.54m² | ~19 | Large patios, linear/contemporary style |
| 900 x 600mm | 0.54m² | ~19 | Large patios, same as above rotated |
Worked example: A 4m x 3m patio with 600 x 600mm slabs
A patio 4m long and 3m wide has an area of 12m². Each 600 x 600mm slab covers 0.36m², so the base number of slabs is 12 ÷ 0.36 = 33.3, rounded up to 34 slabs. Adding 10% for wastage gives 34 × 1.1 = 37.4, rounded up to 38 slabs total.
At the time of writing, budget concrete slabs cost roughly £15–£25 per m², so materials for this patio would be around £180–£300. Mid-range textured concrete or basic natural stone would be £300–£540, and premium porcelain or Indian sandstone would be £540–£960. These are supply-only figures — a professional fitter would typically add labour of £50–£100 per m² on top.
Common mistakes when ordering paving slabs
- Measuring the patio in feet and converting to metres incorrectly. Always measure in metres for the calculator — a 10ft x 8ft patio is 3.05m x 2.44m, not 3m x 2.5m, and that small difference adds up across a large area.
- Choosing a slab size that creates too many small cuts. On a 3m-wide patio, 450mm slabs need 6.67 cuts across the width, while 600mm slabs need exactly 5. Smaller slabs mean more cutting, more wastage, and a busier finished look.
- Forgetting to account for a border or edge restraint. If you’re laying a border of a different slab or using a soldier course, measure that separately and order those slabs in addition to the main area calculation.
- Ordering exactly the calculated number with no spare. A 10% wastage allowance is a minimum — if your patio has many curves, angles or a complex pattern, consider 15% to avoid running out mid-job.
- Assuming all slabs in a pack are exactly the same size. Budget concrete slabs can vary by a few millimetres, which affects the final joint width and can throw off your layout. Check the tolerances on the product spec before ordering.
What to look for when buying paving slabs
Slab thickness matters more than most people realise. For a standard domestic patio taking foot traffic and garden furniture, 35–40mm concrete slabs are the norm. If you want the same slab to double as a driveway or support a heavy hot tub, look for 50mm+ slabs or ones with a specific vehicular rating. Thinner slabs (20–25mm) are fine for footpaths and balconies but will crack under heavy loads.
Surface finish affects both look and safety. Riven or textured concrete slabs offer better slip resistance when wet, which matters on a UK patio that sees rain and moss growth. Polished or smooth natural stone looks premium but can be dangerously slippery when algae builds up. If you have children or elderly users, prioritise a textured or bush-hammered finish over a polished one.
Finally, think about colour consistency. Budget concrete slabs often have noticeable batch variation — order all the slabs you need in one go from the same batch number if possible, and check the supplier’s returns policy before buying. Natural stone like sandstone or limestone has inherent colour variation, which is part of the appeal, but some slabs can be much darker or lighter than the showroom sample.
More questions answered
Do I need planning permission for a patio?
Most garden patios count as permitted development and don’t need planning permission, provided the patio (combined with any other hard surfacing) doesn’t take the total covered area of the garden over 50%. If your patio will raise the ground level significantly, sit close to a boundary, or your property has restrictive covenants or is a listed building, it’s worth checking with your local council first.
How thick should patio slabs be?
For a standard domestic patio taking foot traffic and garden furniture, 35-40mm concrete slabs are typical. If the patio will need to support a driveway, hot tub, or heavier loads, look for thicker slabs (50mm+) or ones specifically rated for vehicular use.
What base do I need under paving?
A typical patio build is a compacted sub-base of MOT Type 1 hardcore (75-100mm), topped with a bed of sharp sand and cement mortar (or a semi-dry mortar mix) that the slabs are laid on. Good drainage and a slight fall away from the house (roughly 1:80) are essential to stop water pooling or running into your home.
How much extra should I order for cutting and wastage?
We build in a 10% allowance on top of the raw number of slabs needed to cover your patio area, which typically covers cuts around edges, breakages during laying, and any mistakes. Irregular patio shapes or intricate patterns may need a slightly higher allowance.
Can I lay paving slabs on soil?
No — laying slabs directly onto soil is the most common cause of patio failure in the UK. Without a proper compacted sub-base, the ground will move with frost heave and rain, causing slabs to sink, tilt or crack. Always excavate to at least 150mm below finished patio level, lay a compacted MOT Type 1 base, and add a sand or mortar bed before the slabs.
What jointing material should I use?
For most domestic patios, kiln-dried sand brushed into the joints is the simplest option, but it needs topping up every year or two. A resin-based jointing compound is more expensive but stays in place longer and resists weed growth. For a traditional look, a cement mortar mix works well, but it must be mixed to the right consistency and tooled properly to avoid cracking.
Should I seal my patio after laying?
Sealing isn’t essential for most patios, but it can help prevent staining from oil, food or moss, and it makes cleaning easier. If you do seal, use a breathable sealant designed for paving — non-breathable sealants trap moisture inside the slab and can cause flaking in freeze-thaw cycles. Seal after the patio has fully cured (at least 4 weeks for mortar beds).
How long does it take to lay a patio?
A straightforward 20m² patio laid by an experienced DIYer with help typically takes 2–3 days for excavation, base preparation and slab laying, plus a day for jointing. A professional team can usually complete the same area in 1–2 days. Allow extra time for complex shapes, curves, or if you’re learning as you go.