Concrete Volume & Bags Calculator
Use our free online Concrete Calculator to perform fast, accurate calculations with instant formulas, step-by-step arithmetic, and verified reference benchmarks.
Concrete Calculator
Instant Live Computation • Zero Waiting
Adjust inputs on the left for instantaneous live computation.
How to Calculate: The Concrete Calculator Formula
Calculates volume in cubic feet and divides by 27 to convert to cubic yards. One 80 lb bag yields 0.60 cu ft; one 60 lb bag yields 0.45 cu ft.
Step-by-Step Calculation Guide
- Input slab length and width in feet.
- Input concrete slab thickness in inches (4 inches is standard for residential patios and driveways).
- Add a 10% safety buffer for uneven subgrade.
- Review total cubic yards for ready-mix truck delivery, or bag counts for DIY.
Practical Concrete Calculator Examples
10 ft by 10 ft patio slab, 4 inches deep.
24 ft × 24 ft at 5 inches deep.
Concrete Slab Dimension to Cubic Yards & Bags Chart
Official reference values and benchmark classifications based on standard institutional guidelines.
| Slab Dimension (ft) | Square Feet | Cubic Yards Needed | 80-lb Bags | 60-lb Bags |
|---|---|---|---|---|
| 6 × 6 ft | 36 sq ft | 0.44 cu yd | 20 Bags | 27 Bags |
| 8 × 8 ft | 64 sq ft | 0.79 cu yd | 36 Bags | 48 Bags |
| 10 × 10 ft | 100 sq ft | 1.23 cu yd | 56 Bags | 75 Bags |
| 12 × 12 ft | 144 sq ft | 1.78 cu yd | 80 Bags | 107 Bags |
| 15 × 20 ft | 300 sq ft | 3.70 cu yd | 167 Bags | 222 Bags |
Frequently Asked Questions about Concrete Calculator
How many 80-pound bags of concrete are in a cubic yard?
It takes exactly 45 bags of 80-pound concrete (or 60 bags of 60-pound concrete) to make one cubic yard.
What is the standard concrete thickness for walkways vs driveways?
Walkways and residential patios are typically poured 4 inches thick. Driveways supporting passenger vehicles should be 4 to 5 inches, and heavy truck driveways 6 inches with rebar.
When should you order a ready-mix concrete truck vs mixing bags?
For jobs requiring more than 1.5 to 2.0 cubic yards (over 70 to 90 bags), ordering a ready-mix truck delivery is significantly faster, structurally more consistent, and less labor-intensive.
How long does concrete take to cure?
Concrete achieves roughly 70% of its compressive strength in 7 days, and reaches full 28-day design strength (e.g. 3,000 to 4,000 PSI) at 28 days.