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
A patio estimate starts with the finished size and slab depth. Enter the overall dimensions of the patio and the concrete thickness you intend to use. If the shape isn’t rectangular, build the area from separate rectangles and remove any sections that won’t be concreted.
Decide what will sit beneath and within the slab. Include the sub-base depth if you want the aggregate requirement calculated, and add mesh reinforcement where it forms part of the patio design. Use the sheet dimensions and overlap specified for the job rather than relying on defaults where you have more accurate information.
The concrete quantity includes your chosen allowance for site losses. Once the material quantities are known, current supplier prices can be entered to estimate the cost of the concrete, sub-base, reinforcement and finish.
For more complicated patios, Advanced Mode can combine several sections and deductions and allows the standard sub-base and mesh assumptions to be changed
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. After the patio has been poured, use our concrete drying and curing calculator to estimate curing milestones based on the concrete and site conditions.
- 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. If you’re also installing concrete kerbs or edging around the patio, use our kerb & edging concrete calculator to estimate the concrete required for the bedding layer and haunches.
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. If your patio design specifies mesh reinforcement, use our reinforcement mesh calculator to estimate the number of sheets, overlaps, layers and wastage required.
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.
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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.