Concrete Slab Cost Calculator
Yards, bags, rebar and total cost for a concrete slab.
Enter your values
Enter the slab length in ft.
Enter the slab width in ft.
Enter the thickness in in.
Enter the delivered price per yard in $.
Enter the labour per sq ft in $.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Concrete needed
- 3.26 cubic yards
- 80 lb bags (DIY option)
- 134
- Concrete cost
- $521.48
- Labour
- $720.00
- Total project
- $1,241.48
- Slab area
- 240 sq ft
Working
- 120 x 12 x 0.33 / 27 = 2.96 yd3, +10% = 3.26
Quick answer
Volume = length x width x thickness / 27 cubic yards. Add 10% for uneven subgrade, then price by the yard delivered or by the bag.
yd3 = L x W x (thickness/12) / 27
At a glance
| What it does | Yards, bags, rebar and total cost for a concrete slab. |
|---|---|
| Category | Home & DIY |
| Inputs needed | Slab length, Slab width, Thickness, Delivered price per yard, Labour per sq ft |
| Main output | Concrete needed |
| Formula | yd3 = L x W x (thickness/12) / 27 |
| Cost | Free — no sign-up, no download |
How to use the Concrete Slab Cost Calculator
- 1Measure the slab footprint and choose a thickness: 4 in for patios, 5 to 6 in for driveways and garages.
- 2Add 10% for subgrade variation - running short mid-pour is expensive.
- 3Compare bag cost to ready-mix; ready-mix usually wins above about 1 cubic yard.
Inputs explained
- Slab length(ft)
- Enter the slab length in ft.
- Slab width(ft)
- Enter the slab width in ft.
- Thickness(in)
- Enter the thickness in in.
- Delivered price per yard($)
- Enter the delivered price per yard in $.
- Labour per sq ft($)
- Enter the labour per sq ft in $.
Worked example
Using the values the calculator loads with:
Inputs
- Slab length20 ft
- Slab width12 ft
- Thickness4 in
- Delivered price per yard160 $
- Labour per sq ft3 $
Results
- Concrete needed3.26 cubic yards
- 80 lb bags (DIY option)134
- Concrete cost$521.48
- Labour$720.00
- Total project$1,241.48
- Slab area240 sq ft
- 20 x 12 x 0.33 / 27 = 2.96 yd3, +10% = 3.26
Frequently asked questions
How thick should a concrete slab be?
4 inches for foot traffic and sheds, 5 to 6 inches with rebar for vehicles, and thicker with an engineered design for heavy equipment.
Do I need rebar or mesh?
Mesh or fibre for a patio; #4 rebar at 18 inch centres for driveways and anything carrying vehicles.
What do I need to enter into the Concrete Slab Cost Calculator?
Just 5 values: slab length, slab width, thickness, delivered price per yard, labour per sq ft. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Concrete Slab Cost Calculator work out the answer?
Volume = length x width x thickness / 27 cubic yards. Add 10% for uneven subgrade, then price by the yard delivered or by the bag. It applies the formula yd3 = L x W x (thickness/12) / 27 and shows the working so you can check each step by hand.
Is the Concrete Slab Cost Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.