Estimate slabs, sub-base, and costs for your patio project
A well-built patio transforms a garden, creating an outdoor living space for dining, entertaining, and relaxing. Whether you are planning a modest seating area or a large entertaining space, getting the material quantities right from the start prevents costly mid-project trips to the builders merchant and ensures your budget stays on track. This patio calculator estimates everything you need for a complete patio project: the number of paving slabs based on your chosen slab size, the sub-base aggregate (MOT Type 1), mortar for bedding, and a realistic cost range from budget to premium. The calculator uses standard UK slab sizes (450x450mm, 600x300mm, 600x600mm, and 900x600mm) and includes a 5% waste allowance for cutting and breakage. Costs for patio projects vary significantly depending on the slab material, preparation required, and whether you are hiring a professional or doing it yourself. Budget concrete slabs start around 20 pounds per square metre for the slabs alone, while premium natural stone can exceed 80 pounds per square metre. Labour adds another 25 to 60 pounds per square metre depending on complexity and location. This calculator provides budget, mid-range, and premium estimates to help you plan your spend.
To estimate your patio requirements: 1. Enter the patio length in metres. Measure the longest dimension of the area you want to pave. 2. Enter the patio width in metres. For an L-shaped patio, calculate each rectangular section separately and add the results. 3. Select your slab size. The 600x600mm size is the UK's most popular choice for patios, offering a good balance of coverage speed and weight. Larger 900x600mm slabs look contemporary but are heavier to handle. Smaller 450x450mm slabs are easier to manage alone. 4. Choose whether to include a sub-base. A proper sub-base (100mm of compacted MOT Type 1) is strongly recommended for any patio. Only deselect this if you have an existing concrete base or are laying over a sound, level hardstanding. 5. Review the results. The calculator shows the number of slabs, sub-base tonnage, mortar bags, and three cost estimates (budget, mid-range, and premium). Use these figures to plan your purchases and compare quotes from landscaping contractors.
The patio calculation covers four aspects of the project: Slab quantity: Slab area (m2) = (slab length / 1000) x (slab width / 1000) Slabs needed = ceiling(patio area / slab area x 1.05) The 1.05 multiplier adds 5% for cutting waste and breakage. Sub-base (if included): Sub-base volume (m3) = patio area x 0.1 (100mm depth) Sub-base weight (tonnes) = volume x 1.8 (MOT Type 1 density) Mortar (if sub-base included): Mortar bags = ceiling(area x 0.5) This assumes a standard bedding mortar application rate of 0.5 bags per m2. Cost estimates per m2: - Budget: slabs 20, sub-base 15, labour 25 = 60 per m2 - Mid-range: slabs 40, sub-base 15, labour 40 = 95 per m2 - Premium: slabs 80, sub-base 15, labour 60 = 155 per m2
Inputs: Length: 5 m, Width: 4 m, Slab size: 600x600, Include sub-base: Yes
Inputs: Length: 3 m, Width: 3 m, Slab size: 450x450, Include sub-base: No
Inputs: Length: 8 m, Width: 5 m, Slab size: 900x600, Include sub-base: Yes
The key to a long-lasting patio is thorough ground preparation. Excavate to a minimum depth of 200mm (100mm sub-base + 50mm mortar bed + 50mm slab), ensuring a consistent fall of 1:80 away from the house for drainage. Compact the MOT Type 1 sub-base in 50mm layers using a vibrating plate compactor. Bed slabs on a full mortar bed (not five-spot) for the strongest result, especially with large-format slabs. Natural stone slabs (Indian sandstone, limestone, granite) should be primed on the back with an SBR-based slurry to prevent staining from the mortar. Allow 10-15mm joints between slabs and point with a suitable jointing compound once all slabs are laid. Most UK patio projects are best done between April and October to avoid frost damage to fresh mortar.