Concrete Calculator
Calculate how much concrete you need in cubic yards, plus the number of premixed bags required.
About the Concrete Calculator
Ordering too little concrete stalls a pour halfway through, and ordering too much wastes money — this calculator converts a slab's length, width, and thickness into the exact volume of concrete needed, plus how many premixed bags that translates to if you're not ordering from a truck.
How It Works
The calculator multiplies length by width by thickness (converted from inches to feet) to get cubic feet, then divides by 27 to convert to cubic yards, the standard unit ready-mix concrete is sold in. It also divides the cubic feet figure by the yield of standard 60-pound and 80-pound premixed bags to estimate bag counts.
Cubic Feet = Length × Width × (Thickness ÷ 12); Cubic Yards = Cubic Feet / 27; 60lb bags ≈ Cubic Feet / 0.45; 80lb bags ≈ Cubic Feet / 0.6.
Example
Scenario: A 10ft × 10ft slab poured 4 inches thick.
Result: About 1.23 cubic yards needed, or roughly 74 sixty-pound bags / 56 eighty-pound bags if using premixed bags instead of a truck.
Assumptions & Limitations
- Assumes a uniformly flat slab with consistent thickness across the entire area, with no allowance for waste built in.
- Bag yield figures are standard manufacturer approximations for 60lb and 80lb premixed concrete bags.
- Most contractors add 5-10% extra to the calculated volume to account for spillage, uneven subgrade, and form leakage — order accordingly.
- Does not account for rebar, mesh, or other reinforcement that displaces a small amount of concrete volume.