Concrete Slab
Cost Calculator
Turn slab dimensions into concrete volume and a practical cost estimate. Start simple, then add your own prices and optional extras.
Price sources & assumptions
How to calculate concrete slab cost
Use this concrete slab cost calculator to estimate a patio, shed base, garage floor or driveway. Enter the length, width and thickness, check your project country in the bottom-right settings, and calculate. The result separates the concrete supply cost from labor and any extras you choose.
For a fast starting point, leave Quick estimate selected. For a contractor quote comparison, choose Detailed estimate and replace the starting concrete and labor rates. Both views use the same formula, so opening the extra fields does not change your budget.
Concrete yd³ = length ft × width ft × thickness in ÷ 324
Concrete m³ = length m × width m × thickness mm ÷ 1,000
Order volume = net volume × (1 + waste ÷ 100)
Total = (concrete + labor + selected extras + fees) × (1 + tax ÷ 100)
For example, a 20 × 20 ft slab at 4 inches is 400 ft² and needs 4.94 yd³ before overage, or 5.43 yd³ with 10% added. At an illustrative $175 per yard and $3 per square foot for labor, that is about $951 of concrete plus $1,200 of labor: $2,151 before base preparation, reinforcement, delivery and tax. These are example inputs, not a national installed-cost quote.
Concrete slab estimates for common sizes
Compare quantities before comparing prices. These volumes assume an even 4-inch thickness and a 10% overage allowance. Thickened edges, footings and beams need additional concrete.
| Slab size (ft) | Area (ft²) | Net yd³ | With 10% |
|---|---|---|---|
| 10 × 10 | 100 | 1.23 | 1.36 |
| 10 × 12 | 120 | 1.48 | 1.63 |
| 12 × 12 | 144 | 1.78 | 1.96 |
| 12 × 16 | 192 | 2.37 | 2.61 |
| 12 × 24 | 288 | 3.56 | 3.91 |
| 20 × 20 | 400 | 4.94 | 5.43 |
| 20 × 30 | 600 | 7.41 | 8.15 |
| 24 × 24 | 576 | 7.11 | 7.82 |
| 24 × 36 | 864 | 10.67 | 11.73 |
| 30 × 30 | 900 | 11.11 | 12.22 |
| 30 × 40 | 1,200 | 14.81 | 16.30 |
| 30 × 50 | 1,500 | 18.52 | 20.37 |
| 40 × 60 | 2,400 | 29.63 | 32.59 |
A 6-inch slab uses 50% more concrete than a 4-inch slab of the same area. It does not necessarily cost 50% more overall: mobilization, forming and preparation do not all scale with concrete volume. A 24 × 24 ft garage example at 6 inches needs 10.67 yd³ net, or 11.73 yd³ with 10% overage.
4-inch concrete slab cost per square foot
At 4 inches, one cubic yard covers 81 square feet before waste. Divide your concrete price per yard by 81, then apply your overage factor. With the illustrative $175 rate and 10% overage, the concrete alone is about $2.38/ft². Add labor and the actual site costs to get an installed estimate.
What goes into a concrete slab installation cost?
Concrete supply: the volume you plan to order multiplied by your ready-mix price. Mix strength, exposure class, additives, delivery distance and order size can change the rate. A supplier may charge for a minimum load even when the slab uses less concrete.
Labor: an editable rate per square foot or square metre. The starting allowance is modeled, not a verified local bid. Clarify whether a contractor includes basic formwork, placing, finishing, curing and joint cutting. Do not enter an all-inclusive installed price as labor and then add concrete again.
Reinforcement and base preparation: add these when they are in your scope. Mesh, rebar, chairs, aggregate, compaction and excavation can have separate costs. A zero entry means no allowance has been included; it does not mean your slab needs none.
Finishes, delivery and pumping: add incremental decorative work and any quoted transport, pump, short-load or fixed charges. Put removal, disposal or other separately quoted work in fixed fees if needed, and record the scope when sharing the estimate.
Waste and tax: overage increases concrete volume only. It does not inflate slab area or area-based labor. The tax field applies a simple percentage to the entire subtotal. If different lines are taxed differently, use tax-inclusive quotes and leave additional tax at zero.
Concrete prices by country: what the defaults mean
Ready-mix concrete is a local purchase. The bottom-right country setting supports the site's country and territory catalog, but coverage is not the same as verified pricing. Every result identifies its concrete price basis and provides a source link where one is available.
Published references include American Concrete's US supplier price list, CBM's Western Ontario contractor prices, Birmingham Ready Mix's UK guide and MixHub's Australian pricing guide. Their mix specifications, tax treatment and delivery terms differ. They are reference points, not directly comparable national averages.
Other countries use explicitly modeled planning defaults derived from the site's construction factors and exchange-rate data. These have not been independently researched as concrete prices. If a currency conversion is unavailable, enter a local quote; the tool will not silently substitute a dollar amount in a different currency. All starting labor rates are modeled allowances.
Source review: 1 October 2026. Exchange-rate refreshes do not refresh supplier prices. Before ordering, confirm the mix, full delivered price, minimum order, applicable taxes and site access with your supplier.
Patio, shed, garage, driveway or foundation?
The thickness buttons make scenario comparisons faster: Patio 4″, Shed 4″, Garage 6″, Driveway 6″ and Foundation 8″. They set only the thickness. They do not choose concrete strength or design reinforcement, drainage, joints or footings.
Use your approved design for structural work and vehicle loading. This rectangular volume calculator is not a foundation design calculator and does not price a complete foundation system. A suspended slab, raft, post-tensioned slab or frost-protected foundation requires a different scope.
For adjacent budgets, use our garage cost calculator, compare asphalt and concrete driveway costs, or include the slab within your whole-house construction estimate. Avoid adding the same foundation cost twice.
For practical background, the NRMCA Concrete in Practice library covers slab joints, finishing and curing. Good construction details matter alongside the material quantity.
Frequently asked questions
How much would a 20x20 concrete slab cost?
A 20 × 20 ft slab is 400 ft². At 4 inches it needs 4.94 yd³ net or 5.43 yd³ with 10% overage. Multiply the order volume by your local concrete rate, then add labor and selected extras. The worked example above is about $2,151 for concrete and labor only.
How much does it cost to pour a 40x60 slab of concrete?
A 40 × 60 ft slab is 2,400 ft². At 4 inches, allow 29.63 yd³ net or 32.59 yd³ with 10% overage. At 6 inches, allow 44.44 yd³ net or 48.89 yd³ with 10% overage. Use the specified thickness and local quotes; large pours also need a placement plan.
How much does a 12x12 concrete slab cost?
A 12 × 12 ft slab is 144 ft² and requires 1.78 yd³ at 4 inches, or 1.96 yd³ with 10% overage. Minimum-load and mobilization charges can dominate small jobs, so do not scale a large-project price down by area alone.
How many yards of concrete does a 10x10 slab need?
At 4 inches thick, a 10 × 10 ft slab needs 1.23 cubic yards before overage, or about 1.36 cubic yards with 10% added. At 6 inches, the corresponding quantities are 1.85 and 2.04 cubic yards.
How much concrete is needed for a 30x30 slab 4 inches thick?
A 30 × 30 ft slab contains 11.11 cubic yards at 4 inches. A 10% overage allowance brings the estimate to 12.22 cubic yards. Confirm uneven ground, thickened edges and supplier ordering increments before placing the order.
How do I calculate the cost of a 500 sq ft concrete slab?
For a 4-inch slab, divide 500 by 81 to get 6.17 yd³, then add the chosen overage. At 10%, the order estimate is 6.79 yd³. Multiply by the concrete rate and add 500 times your labor and other area-based rates, plus fixed fees and applicable tax.
Does a 6-inch slab need rebar?
Thickness alone does not determine reinforcement. Loads, soil, slab dimensions, joints, exposure and the structural design all matter. Ask the designer or local authority for the required specification; this calculator only prices the allowance you enter.
Do I need gravel under a concrete slab?
The base depends on soil, drainage, frost and the design. A compacted granular base may be specified, but the calculator does not determine its type or depth. Enter the actual preparation allowance and have unsuitable ground assessed before pouring.
Is it cheaper to mix and pour my own concrete?
Doing your own labor can lower the cash outlay, but include bagged mix or delivered concrete, mixer hire, tools, forms, base preparation and disposal. A large pour also depends on adequate labor and timing. Enter zero labor only if you intend to exclude the value of your own work.
Can I use this as a concrete slab foundation cost calculator?
Use it for the flat rectangular concrete portion only. Footings, grade beams, thickened edges, reinforcement design, excavation and engineering need separate quantities or quotes. The Foundation 8-inch button is only an example thickness.
Can I estimate concrete slab costs in Australia, Canada, the UK or India?
Yes. Select the project country and use the local currency rates. Source details identify whether the concrete rate is a supplier benchmark, a published guide or a modeled planning default. Replace it with a current local quote for a closer estimate.
Will concrete prices go down?
There is no reliable universal prediction. Local demand, energy, cement, aggregate, transport and labor can move prices in different directions. Ask suppliers how long their written quote remains valid.
Have a local concrete quote?
Enter it in Detailed estimate to turn a broad starting budget into a project-specific calculation.
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