Concrete Slab Calculator
Estimates concrete volume for a rectangular slab from its length and width in feet and thickness in inches, returning cubic yards, cubic feet, and the approximate number of 60-lb bags.
What this calculator does
The Concrete Slab Calculator estimates your result instantly from the values you enter, using standard construction & home formulas. Estimates concrete volume for a rectangular slab from its length and width in feet and thickness in inches, returning cubic yards, cubic feet, and the approximate number of 60-lb bags. Calculations run in your browser, so nothing you type is sent to a server, and the output is an estimate rather than a certified or official figure.
Result
About Concrete Slab Calculator
Planning a concrete pour? This calculator turns a slab’s length and width in feet plus its thickness in inches into the volume of concrete you need.
It reports the total in cubic yards and cubic feet, then estimates how many 60-lb bags that works out to, so you can weigh bagged mix against ordering ready-mix.
Formula & Mathematical Calculation
Concrete Needed (yd³) = f(Length (ft), Width (ft), Thickness (in))
Calculated according to standard construction formulas implemented in the calculator core.
Calculation Example
For a slab 20 ft long, 10 ft wide and 4 in thick: volume = 20 × 10 × (4 ÷ 12) = 66.67 ft³.
Converting to cubic yards: 66.67 ÷ 27 = 2.47 yd³. Bags = ceil(66.67 ÷ 0.45) = 149 sixty-pound bags. The tool shows 2.47 yd³, 66.67 ft³ and 149 bags.
Key Benefits
- Converts feet-and-inches slab dimensions into cubic yards and cubic feet in one step.
- Estimates the 60-lb bag count so you can compare bagged mix against ready-mix delivery.
- Uses the exact 27 cubic feet per cubic yard conversion.
- Suggests ordering about 10% extra to cover spillage and uneven subgrade.
How to Use this Calculator
-
Enter the slab length
Type the slab length in feet into the Length (ft) field. -
Enter the slab width
Type the slab width in feet into the Width (ft) field. -
Enter the thickness
Type the slab thickness in inches into the Thickness (in) field. -
Calculate
Select Calculate to compute the volume. -
Read the results
Read Concrete Needed in cubic yards, the Cubic Feet total, and the approximate 60-lb bag count in the result boxes.
Assumptions & Limitations
What the calculation assumes
- Every value you enter is treated as an exact, known amount.
- Any rate or interval you enter is assumed to hold for the whole period unless the form asks for it separately.
- Results use standard published formulas and account only for the values entered above.
- Rounding is applied for display; the underlying calculation uses your full precision.
- Results are returned in the same units you enter, unless the tool states the output unit.
What it does not cover
- Concrete Slab Calculator produces a calculated result for reference and learning, not a certified or official measurement.
- Real-world outcomes differ when tolerances, rounding rules or local standards apply.
- Definitions and standards vary by region and change over time; verify the convention that applies to your case.
- Figures are only as accurate as the inputs you supply — check them before acting on the result.
- For work where the result carries real consequences, confirm it against an authoritative source.
Frequently Asked Questions
Free to use, no account needed. Calculations run in your browser, so nothing you type is sent to a server. Results are estimates — how we build and check our calculators.