How to use it
- Enter the slab length and width in feet
- Input the slab thickness in inches
- Enter the price per cubic yard of concrete
- Click calculate to see cubic yards, cost, bags, and cubic feet
This calculator turns your slab's length, width, and thickness into the exact concrete volume you need, then converts that into what matters: cost, bags, and cubic feet. Since a standard 80-lb bag yields about 0.6 cubic feet, the tool uses that constant to show how many bags to buy—no guesswork. The cubic yard figure is what you'll order from a ready-mix supplier, while the bag count is for smaller DIY pours. The estimated cost comes straight from your price per cubic yard and the total volume. Read it this way: if your yardage is 1.5, you're ordering 1.5 cubic yards, and the bag count tells you how many 80-lb bags equal that volume if you're mixing on site. This helps you compare bulk delivery versus bagged concrete, plan your budget accurately, and avoid over- or under-ordering.
Pro tips
- Add 10% waste allowance to your final cubic yards to cover spillage, uneven subgrade, or slight miscalculations
- Always round your bag count up—partial bags don't exist, and mixing an extra partial batch beats running short
- Order ready-mix for anything over 1 cubic yard; hand-mixing that much in a mixer is slow and exhausting
- Double-check your thickness in inches—one missing inch can change your yardage by 20% or more on a large slab
Real-life examples
- Planning a backyard patio and need to know how much concrete to order before the weekend
- Budgeting a concrete driveway replacement and comparing ready-mix versus bagged costs
- Estimating materials for a shed foundation to quote a handyman job accurately
Case study
Dana needed a 10x12 shed slab, 4 inches thick. She guessed 2 cubic yards and nearly overpaid by half. Using the calculator, she entered her dimensions and local price per yard—it showed 1.48 cubic yards and 133 bags. She ordered 1.6 yards with waste, saved $86, and finished exactly on budget.