Concrete Calculator
Concrete Needed
1.36 cubic yards
36.7 cubic feet • includes 10% waste factor
80 lb Bags
62
60 lb Bags
82
40 lb Bags
123
Est. Ready-Mix Cost
$170 – $217
Tip: For projects over 1 cubic yard, ready-mix delivery ($125–$160/cu yd) is more economical than buying bags. For small projects under 0.5 cu yd, pre-mixed bags are more practical.
Disclaimer: Estimates are for budgeting purposes only. Actual costs vary by location, contractor, material availability, and project complexity. Always get professional quotes for exact pricing.
Concrete Bags Reference
| Bag Size | Yield (cu ft) | Bags per Cu Yd | Approx. Cost / Bag |
|---|---|---|---|
| 40 lb | 0.30 cu ft | 90 bags | $3.50 – $5.00 |
| 60 lb | 0.45 cu ft | 60 bags | $4.50 – $6.00 |
| 80 lb | 0.60 cu ft | 45 bags | $5.50 – $7.50 |
Common Project Volumes
| Project | Typical Size | Cubic Yards | 80 lb Bags |
|---|---|---|---|
| Sidewalk | 4 × 30 ft, 4″ thick | 1.5 cu yd | ~67 bags |
| Patio Slab | 12 × 12 ft, 4″ thick | 1.8 cu yd | ~80 bags |
| Driveway | 20 × 20 ft, 6″ thick | 8.1 cu yd | ~367 bags |
| Garage Floor | 24 × 24 ft, 6″ thick | 11.7 cu yd | ~528 bags |
How We Calculate
Our concrete calculator estimates the volume of concrete needed based on shape, dimensions, quantity, and a 10% waste factor. Results are shown in cubic yards, cubic feet, and number of pre-mixed bags.
How the math works: For slabs and footings: Volume = length × width × (thickness ÷ 12). For cylinders/tubes: Volume = π × (diameter ÷ 24)² × height. All volumes include a 10% waste factor. Bag counts: 80 lb = 0.60 cu ft yield, 60 lb = 0.45 cu ft, 40 lb = 0.30 cu ft. Ready-mix cost estimate uses $125–$160 per cubic yard.
Shape Guide
Slab / Rectangle: Most common — patios, sidewalks, driveways, garage floors. Enter length, width (feet), and thickness (inches).
Footing / Trench: Continuous footings for walls and foundations. Enter length, width (feet), and thickness (inches).
Column / Pier: Square or rectangular piers. Enter length, width (feet), and height (feet).
Sono Tube / Cylinder: Round tube forms for deck posts and footings. Enter diameter (inches) and height (feet).
Data Sources
Ready-mix pricing based on 2025 national averages from concrete batch plants and contractor estimates. Bag yields per manufacturer specifications (Quikrete, Sakrete). We review and update data regularly.
Last updated: 2026-02-08
Frequently Asked Questions
How much concrete do I need? +
Calculate volume: length (ft) × width (ft) × thickness (in) ÷ 12, then divide by 27 to get cubic yards. Add 10% for waste. For example, a 10×10 ft slab at 4 inches thick: 10 × 10 × 0.33 = 33.3 cu ft ÷ 27 = 1.23 cu yd. With 10% waste: ~1.36 cu yd.
How many bags of concrete do I need? +
An 80 lb bag yields 0.6 cubic feet, a 60 lb bag yields 0.45 cu ft, and a 40 lb bag yields 0.30 cu ft. For 1 cubic yard (27 cu ft): you need 45 bags (80 lb), 60 bags (60 lb), or 90 bags (40 lb). Our calculator factors in 10% waste automatically.
When should I use bags vs. ready-mix concrete? +
Use pre-mixed bags for small projects under 0.5 cubic yards — fence posts, small repairs, and setting mailbox posts. For anything over 1 cubic yard, ready-mix delivery ($125–$160/cu yd) is more economical and ensures consistent quality. The crossover point is around 0.5–1 cu yd.
How thick should a concrete slab be? +
4 inches for patios, walkways, and shed pads. 5 inches for standard residential floors. 6 inches for driveways and areas with vehicle traffic. 8+ inches for structural applications and heavy equipment. Thicker slabs require more concrete but last significantly longer under load.
How much does concrete cost per cubic yard? +
Ready-mix concrete costs $125–$160 per cubic yard delivered (2025 national average). Prices vary by region, PSI strength, and additives. High-strength (4,000 PSI) costs $140–$175/cu yd. Pre-mixed bags cost more per yard but are convenient for small jobs: ~$7/bag × 45 bags = ~$315/cu yd.
What is the 10% waste factor? +
Always order 10% more concrete than calculated. Waste comes from uneven subgrade, spillage, over-excavation, form irregularities, and finishing. For ready-mix, ordering short means an expensive short-load delivery fee. It's cheaper to have a little extra than to order another truck.
How do I calculate concrete for a cylinder or sono tube? +
Volume = π × radius² × height. For a 12-inch diameter sono tube at 4 feet deep: π × 0.5² × 4 = 3.14 cu ft = 0.116 cu yd. With 10% waste: 0.13 cu yd. One 80 lb bag fills about 0.6 cu ft, so you'd need about 6 bags per tube.
How long does concrete take to cure? +
Concrete reaches 50% strength in 3 days, 75% in 7 days, and full strength (design PSI) in 28 days. You can walk on it after 24–48 hours and drive on it after 7 days. Keep concrete moist during the first 7 days for optimal curing — use curing compound or wet burlap.
Related Calculators
Related Guides
Plan Your Next Project
Explore more free calculators to estimate costs and materials for your home improvement projects.