Concrete Calculator
Find out how much concrete you need for a slab, patio or footing — in cubic feet, cubic yards, and the exact number of 60 lb or 80 lb bags.
Results
For large projects, compare bag cost against a ready-mix delivery — anything over about 1 cubic yard is worth pricing out.
How to Use This Concrete Calculator
- Enter the length and width of your slab in feet.
- Enter the depth in inches (not feet — the calculator converts automatically).
- Keep the 10% allowance, or adjust it down for clean, level forms.
The calculator multiplies length × width × depth to get cubic feet, then converts to cubic yards (27 cu ft = 1 cu yd) and works out bag counts using standard bag yields.
Bag Coverage: 60 lb vs 80 lb
| Bag size | Yield per bag | Bags per cubic yard | Coverage at 4 in thick |
|---|---|---|---|
| 60 lb | 0.45 cu ft | ~60 bags | 1.35 sq ft per bag |
| 80 lb | 0.60 cu ft | ~45 bags | 1.80 sq ft per bag |
How Thick Should Your Concrete Be?
- 4 inches: patios, walkways, shed and hot tub pads, small footings.
- 5–6 inches: driveways, garage floors and areas with vehicle traffic.
- 8–12 inches: structural footings, retaining walls and load-bearing piers — confirm with local code.
Bags or Ready-Mix?
Bagged concrete is convenient for small jobs, but it is labor-intensive: one 80 lb bag is roughly a third of a wheelbarrow. As a rough guide, once your project passes about 1 cubic yard (45+ bags of 80 lb), call a local ready-mix supplier for a delivery quote — it is usually cheaper per yard and saves hours of mixing.
Frequently Asked Questions
How many bags of concrete do I need for a 10x10 slab 4 inches thick?
A 10×10 slab 4 inches thick is about 33.3 cubic feet. That works out to 56 bags of 80 lb concrete or 75 bags of 60 lb concrete before adding waste.
How many 80 lb bags of concrete are in a cubic yard?
One cubic yard is 27 cubic feet. An 80 lb bag makes about 0.6 cubic feet, so you need about 45 bags per cubic yard.
How many 60 lb bags of concrete are in a cubic yard?
A 60 lb bag makes about 0.45 cubic feet, so one cubic yard takes about 60 bags.
How thick should a concrete slab be?
4 inches is standard for patios, sidewalks and shed bases. Driveways and areas that support vehicles should be 5–6 inches thick with proper reinforcement.