How to use it
- Enter length in feet.
- Enter width in feet.
- Enter thickness in inches.
- Read cubic yards, bags, and cubic feet results.
This calculator tells you exactly how much concrete you’ll need for a 30‑by‑30‑foot slab. You input the slab’s length, width, and thickness, and it instantly converts those dimensions into cubic feet, then into cubic yards (27 ft³ per yard) and the number of 80‑lb bags (each bag gives about 0.6 ft³). Knowing the yardage helps you order the right amount from the supplier, avoiding costly over‑orders or shortfalls. The bag count lets you compare prices per bag and plan delivery. Read the three results: cubic feet for on‑site volume checks, cubic yards for the concrete order, and bags for budgeting. You can also factor in a 5‑10% waste allowance to ensure you have enough material for cuts and uneven subgrade. The tool works on any device, so you can check estimates on the job site or at home.
Pro tips
- Add 5‑10% extra for waste to cover cuts and spillage
- Round up the bag count to the next whole bag
- Order concrete a day early to avoid delivery delays
- Double‑check thickness conversion from inches to feet
Real-life examples
- Homeowner planning a 30x30 patio
- Contractor estimating material for a small commercial slab
- DIY enthusiast building a garage floor
Case study
Mike needed a 30x30 garage floor 4 in thick. Using the calculator he saw he required 1.78 yd³, about 80 bags. He ordered 85 bags, avoided a second delivery, and finished on schedule.