Concrete Calculator & Cost Estimator
Type your dimensions → get exact bag count + the math shown. Seconds. No signup.
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Frequently asked questions
- How many 80 lb concrete bags do I need?
- Divide your volume in cubic feet by the bag yield (80 lb ≈ 0.60 ft³ per bag), add your waste factor, then round up. Our calculator does this live — e.g. a 12×10×4 in slab with 10% waste needs 74 bags.
- Should I buy bags or ready-mix?
- Small jobs under ~1 yd³ are usually cheaper and easier with bags. Larger slabs and driveways are ordered by the cubic yard from a ready-mix supplier. We show both bag count and order-ready yards.
- Why include a waste factor?
- Spillage, uneven subgrade, and partial bags mean you rarely use every ounce. A 10% waste default helps you avoid a second trip to the store — you can adjust from 0–15%.
- How do I convert inches of thickness to cubic yards?
- Multiply length × width × thickness (in feet), divide by 27. Thickness in inches is divided by 12 first. See our Methodology page for the full formula and sources.