How to use it
- Enter your form's length in feet.
- Enter your form's width in feet.
- Enter the thickness in inches.
- Click Calculate to see cubic yards, bags, and cubic feet.
This concrete form calculator tells you exactly how much concrete you need for any slab, footing, or form. Enter the length, width, and thickness, and it instantly returns the volume in cubic yards, the number of standard 80-lb bags, and the total cubic feet. That matters because ordering too little means a cold joint; ordering too much means wasted money and material. The calculator uses a standard 80-lb bag yield of 0.6 cubic feet, so the bag count is accurate for typical concrete mix. Read the results this way: cubic yards is what you'll order from a ready-mix plant, bags are what you'd use for small or DIY jobs, and cubic feet helps you compare against mixer capacity or wheelbarrow volume. No guesswork, no over-ordering — just the right amount for your project.
Pro tips
- Add 10% extra to your final bag count for waste, spillage, or slight depth variations.
- Always round up to the nearest full bag — concrete suppliers won't sell a partial bag.
- Order ready-mix for jobs over 1 cubic yard; bags are more cost-effective for smaller pours.
- Double-check all measurements are in the same units before calculating — mixing feet and inches is a common error.
Real-life examples
- A 10x10 patio slab at 4 inches thick needs exactly 1.23 cubic yards and 67 bags.
- A 2x2x2-foot footing for a deck post requires 0.3 cubic yards or 15 bags.
- A 3-foot-wide, 20-foot-long walkway at 4 inches thick takes 0.74 cubic yards and 40 bags.
Case study
A homeowner planned a 12x12 patio at 4 inches thick. They used the calculator and saw 1.78 cubic yards and 80 bags. They ordered 88 bags to cover waste, finished the pour without running short, and had just one bag left over.