Concrete Patio Calculator
Estimate the concrete, sub-base, reinforcement and total material cost for your concrete patio.
- Slab thickness: 100 mm
- Concrete wastage allowance: 10%
- Sub-base density: 2,000 kg/m³
- Loose sub-base allowance: 20%
- Mesh overlap: 300 mm
- Labour, excavation, delivery, plant hire and disposal costs are excluded.
- Results are for planning and estimation purposes only — not a structural specification.
Use this concrete patio calculator to estimate the amount of concrete needed for a new patio, together with optional sub-base, reinforcement and finish costs. Enter the patio dimensions, choose a slab thickness and add a wastage allowance to calculate the net area, perimeter, base concrete volume and recommended order volume.
The calculator supports metric and imperial measurements. Standard mode is designed for a straightforward rectangular patio, while Advanced mode can combine several rectangular sections, subtract rectangular openings and use custom assumptions for sub-base density, loose material allowance and mesh overlap.
You can also enter current supplier prices to produce an itemised material estimate in pounds sterling. The result is a planning estimate rather than a quotation, so check measurements, site conditions, access and supplier minimum-order charges before buying materials.
PRO TIP: Measure the excavation rather than relying only on drawing dimensions, and obtain current prices from the supplier that will actually deliver to the site. Ask about minimum loads, part-load charges, delivery access and discharge time. For an irregular patio, divide the shape into simple rectangles in Advanced mode, then use deductions for rectangular areas that will not be concreted.
How to use this calculator
Choose the unit system
Metric mode uses metres for length and width, millimetres for slab and sub-base depths, cubic metres for concrete, and square metres for finish pricing. Imperial mode accepts feet and inches, displays concrete in cubic yards and uses square feet for finish pricing. The calculator converts all values internally before calculating.
Enter the patio dimensions
For a single rectangular patio, enter the overall length and width. Both values must be greater than zero. In imperial mode, the inches field must remain below 12.
Select the slab thickness
Choose 75 mm, 100 mm, 125 mm or 150 mm, or select Custom thickness. The calculator defaults to 100 mm. The correct depth depends on the intended use, ground conditions, preparation and design specification; do not increase or reduce thickness solely to match a budget.
Add a wastage allowance
The default wastage allowance is 10%, and the permitted range is 0% to 30%. This allowance increases the concrete order volume to cover minor measurement errors, uneven excavation and spillage.
Enter concrete pricing
Enter the supplier’s concrete price per cubic metre in metric mode or per cubic yard in imperial mode. The calculator multiplies the recommended order volume by this rate. Delivery charges, waiting time, part-load fees, pumping and labour are not added automatically.
Include a sub-base
The sub-base option is enabled by default. Enter the compacted depth and a cost per tonne. Standard mode assumes a density of 2,000 kg/m³ and a 20% loose material allowance. Advanced mode lets you change both values.
Add reinforcement
Choose Mesh sheets to include reinforcement. Select a 3.6 m × 2.0 m sheet, a 4.8 m × 2.4 m sheet or a custom sheet size, then enter the price per sheet. Standard mode assumes 300 mm overlap; Advanced mode allows a custom overlap.
Add finish and other material costs
Select the relevant finish type and enter any additional finish cost per square metre or square foot. Available labels include standard, coloured, stamped, exposed aggregate and custom finish. You can also add one combined figure for other materials.
Use Advanced mode for complex layouts
Select Multiple rectangular sections to add extra rectangles to the main patio. Their areas and perimeters are added to the calculation. Rectangular deductions can be used for openings or excluded areas; each deduction has a length, width and quantity. The total deduction area must remain smaller than the gross patio area.
Results Explanation
| Result | What it means |
|---|---|
| Area | The net patio area after any rectangular deductions. Displayed in m² or ft². |
| Perimiter | The sum of the perimeters of all included rectangular sections. Deductions do not reduce this figure. |
| Base concrete | The concrete volume before wastage, calculated from net area × slab thickness. |
| Concrete to order | The base concrete volume increased by the selected wastage percentage. |
| Sub-base | Compacted volume, loose volume and estimated weight in tonnes, when sub-base is included. |
| Mesh sheets | The number of whole sheets required after allowing for the effective sheet area created by overlap. |
| Concrete cost | Recommended concrete order volume multiplied by the entered concrete unit price. |
| Sub-base cost | Estimated sub-base tonnes multiplied by the entered price per tonne. |
| Reinforcement cost | Whole mesh sheets multiplied by the entered price per sheet. |
| Finish cost | Net patio area multiplied by the entered additional finish rate. |
| Other material cost | The fixed additional amount entered by the user. |
| Total material cost | Concrete, sub-base, reinforcement, finish and other material costs added together. |
| Cost per area | Total material cost divided by the net patio area. |
How the Maths Works
The calculator converts the selected units to metres, square metres and cubic metres for the main calculation, then converts the displayed results back to the chosen unit system.
Patio area and perimeter
Gross area = sum of each rectangular section’s length × width
Deduction area = sum of deduction length × width × quantity
Net area = gross area − deduction area
Perimeter = sum of 2 × (length + width) for each included patio rectangle
Concrete volume
Base concrete volume = net area × slab thickness
Concrete to order = base concrete volume × (1 + wastage percentage ÷ 100)
Concrete cost = concrete to order × concrete unit price
Sub-base quantity
Compacted sub-base volume = net area × compacted sub-base depth
Loose sub-base volume = compacted volume × (1 + loose material allowance ÷ 100)
Sub-base tonnes = loose volume × density in kg/m³ ÷ 1,000
Sub-base cost = sub-base tonnes × cost per tonne
Mesh reinforcement
Effective sheet length = sheet length − overlap
Effective sheet width = sheet width − overlap
Effective sheet area = effective sheet length × effective sheet width
Mesh sheets = net patio area ÷ effective sheet area, rounded up to the next whole sheet
Mesh cost = whole sheets × cost per sheet
Finish and total cost
Finish cost = net patio area × finish cost per unit area
Total material cost = concrete + sub-base + mesh + finish + other material costs
Cost per area = total material cost ÷ net patio area
Common Mistakes to Avoid
- Using finished patio dimensions without checking the actual excavated area.
- Mixing metres with millimetres, or entering inches as a decimal part of a foot.
- Forgetting that the selected wastage percentage increases the concrete order volume.
- Entering a sub-base depth as loose depth when the field requires compacted depth.
- Assuming the default density and loose allowance match every aggregate product.
- Counting mesh by its full sheet area even though overlaps reduce effective coverage.
- Treating the material total as a full installed price.
- Ignoring delivery, pumping, access, formwork, membranes, joints, drainage and labour.
- Subtracting an opening that is equal to or larger than the gross patio area.
- Using the calculated perimeter as a full formwork quantity without checking shared edges and deductions.
faqs
How much concrete do I need for a patio?
Multiply the net patio area by the slab thickness to find the base volume, then add a sensible wastage allowance. This calculator performs those steps and shows both the base volume and the recommended order volume.
What thickness should a concrete patio be?
The calculator offers 75 mm, 100 mm, 125 mm and 150 mm presets plus a custom option. The appropriate thickness depends on loading, ground conditions, sub-base preparation and the project design. Seek professional advice where the slab will carry unusual loads or forms part of structural work.
How much wastage should I allow for concrete?
The calculator defaults to 10% and accepts 0% to 30%. The suitable allowance depends on measurement confidence, excavation accuracy, access and the risk of spillage or uneven depth.
Do I need a sub-base under a concrete patio?
A well-prepared, compacted base is commonly important for a durable external slab, but the required build-up depends on soil, drainage, expected loading and local site conditions. The calculator can estimate sub-base volume and weight when the option is included.
Does a concrete patio need reinforcement?
Not every patio uses mesh, but reinforcement may be specified to help control cracking or suit loading and ground conditions. The calculator estimates mesh sheets only when Mesh sheets is selected; it does not design reinforcement.
How does the calculator handle an L-shaped patio?
Use Advanced mode and split the layout into rectangular sections. Add each rectangle separately. Alternatively, calculate a larger rectangle and use a rectangular deduction where that accurately represents the missing area.
Why is the mesh sheet result rounded up?
Mesh is purchased in whole sheets. The calculator divides the net patio area by the effective sheet area after overlap, then rounds up to the next whole sheet.
related calculators
Concrete Footing Calculator – Estimate concrete volume, bags required and material cost for strip, pad and round post footings.
Concrete Driveway Calculator – Estimate concrete volume, sub-base material and material cost for driveway projects.
Screed Calculator – Estimate screed volume, material quantities and coverage for floor levelling and renovation projects.
Concrete Stairs Calculator – Estimate concrete volume, bag quantities, ready-mix concrete and material cost for steps, staircases and landing pads.
Concrete Ramp Calculator – Calculate concrete volume, slope ratios, MOT Type 1 requirements and material costs for concrete ramps.
Concrete Block Fill Calculator – Estimate concrete or grout volume, block count and bags required for concrete block walls.
Concrete Weight Calculator – Estimate concrete weight from dimensions or known volume, including reinforcement, material cost and load limit checks.
Postcrete Calculator – Estimate the Postcrete volume, whole bags and total weight required to set fence posts.
Concrete Column Calculator – Estimate concrete volume, ready-mix, concrete bags, weight and material costs for circular, square, rectangular and tapered concrete columns.
Self-Levelling Compound Calculator – Estimate self-levelling compound volume, bags required, mixing water and material cost for floor levelling projects.
Low Carbon Concrete Calculator – Estimate the embodied carbon of concrete projects, compare different concrete mixes and calculate potential carbon savings.
Kerb & Edging Concrete Calculator – Estimate concrete volume, concrete bags required and material cost for kerb and edging installations.
Concrete Drying & Curing Calculator – Estimate concrete curing milestones, drying times and project dates based on slab thickness and site conditions.
Rebar Calculator – Estimate the quantity, total length, weight and stock bars required for a rectangular reinforcement grid.
Concrete Bags Calculator – Calculate how many bags of concrete you need, including wastage, total weight, supplied volume, leftover concrete and estimated material cost.
Concrete Calculator – Estimate concrete volume, bags required and material cost for slabs, pads, piers and post holes.
disclaimer
This calculator provides an estimate for planning and budgeting. It is not a structural design, engineering specification, supplier quotation or guarantee of the quantity required on site.
Check all measurements and product data before ordering. Concrete and aggregate suppliers may apply minimum loads, rounding rules, delivery charges, waiting-time charges and part-load fees that are not included unless entered manually.
The calculator does not assess soil bearing capacity, settlement, frost risk, drainage falls, damp-proofing, reinforcement design, movement joints, curing, formwork, excavation safety or access for delivery vehicles and pumps.
Concrete is heavy, alkaline and hazardous to skin and eyes. Use suitable personal protective equipment, safe handling methods and competent assistance. Follow supplier safety information and current site procedures.
Where the patio affects a building, drainage route, retaining structure, threshold, boundary or other regulated work, check the applicable UK requirements and obtain professional advice or sign-off where needed.