💡
Quick Answer
For a standard 4-inch thick slab, you need 1.23 cubic yards of concrete per 100 square feet. An 80-pound bag yields 0.60 cubic feet, requiring 45 bags per cubic yard.
🛠️
Essential Tools
Affiliate Disclosure: As an Amazon Associate, we earn from qualifying purchases. We only recommend products relevant to this project.
Stanley FATMAX 25 ft. Classic Tape Measure (33-725)
Industry-standard 25ft tape measure with BladeArmor coating,...
View Product (paid link)3M Safety Glasses
ANSI Z87.1 certified anti-fog polycarbonate safety glasses w...
View Product (paid link)Mechanix Wear: The Original Work Gloves
Gold-standard multi-purpose work glove with synthetic leathe...
View Product (paid link)Empire e70.48 True Blue 48-Inch Professional Aluminum Box Level
Professional-grade 48-inch level with 6061 aircraft aluminum...
View Product (paid link)Stanley FATMAX Folding Retractable Utility Knife (FMHT10502)
Compact folding retractable utility knife with twin blade de...
View Product (paid link)Medium PVC Concrete Mixing Tub
Heavy-duty PVC construction 10-gallon mixing tub for concret...
View Product (paid link)📊 Concrete Volume by Project Type
Standard Slab (4")
Coverage:81 sq ft/yard
Bags needed:45 (80 lb) per yard
Formula: (L × W × 0.33) ÷ 27 = cubic yards
Driveway (6")
Coverage:54 sq ft/yard
IRC minimum:4-5 inches (6" for RV/heavy trucks)
Formula: (L × W × 0.5) ÷ 27 = cubic yards
Footings (12" deep)
Coverage:27 sq ft/yard
IBC standard:12" below soil
Formula: (L × W × 1.0) ÷ 27 = cubic yards
Posts (12" diameter)
Per foot depth:0.785 cubic feet
Per 4' pier:0.116 yards (5.2 bags)
Formula: (π × r² × h) ÷ 27 = cubic yards
📐 Industry Standard Specifications
Bag Yields (ASTM C150)
| Bag Size | Cubic Feet | Bags per Yard |
|---|---|---|
| 80 lb bag | 0.60 cubic feet | 45 bags |
| 60 lb bag | 0.45 cubic feet | 60 bags |
| Cubic yard | 27 cubic feet | — |
Thickness Requirements (IBC/IRC)
Residential Applications
- •Patios/Walkways: 3.5 inches minimum (4" standard)
- •Garage floors: 4-5 inches (6-8" for heavy vehicles)
- •Driveways: 6 inches minimum
- •Foundation walls: 6-8 inches
Footing Depth
- •Frost zones: Below local frost depth
- •Non-frost areas: 12 inches minimum
- •Always verify with local building department
⚠️Waste Factors (ACI 301)
Slabs
5-8%
Footings
10-15%
Walls
7-10%
Stairs
10-12%
🧮 Step-by-Step Calculation
Example: 10' × 20' Patio Slab (4 inches thick)
1
Calculate cubic feet
10 ft × 20 ft × 0.33 ft = 66 cubic feet
2
Convert to cubic yards
66 ÷ 27 = 2.44 cubic yards
3
Add waste factor (8% for slab)
2.44 × 1.08 = 2.64 cubic yards
4
Calculate bags needed (using 80 lb bags)
2.64 × 45 = 119 bags
✓
Order amount
Round up: 120 bags OR order 3 cubic yards ready-mix
🚛 Ready-Mix vs. Bagged Concrete
Ready-Mix Concrete
Delivered by truck
When to use:
- ✓Projects requiring 1+ cubic yards
- ✓Large slabs, driveways, foundations
- ✓Any project over 50 bags
Advantages:
- • Professionally mixed to specifications
- • Consistent strength throughout
- • Faster pour for large projects
- • Cost-effective over 1 yard
Bagged Concrete
Mix-on-site
When to use:
- ✓Small repairs under 1 cubic yard
- ✓Post holes, small footings
- ✓Multiple pours over time
Advantages:
- • Mix only what you need
- • No minimum order
- • Store unused bags
- • Better for small projects
Note: Mixing 45+ bags by hand is extremely labor-intensive
📋 Common Concrete Projects
10' × 10' Patio (4 inches)
Cubic yards:1.23 yards
80 lb bags:55 bags
Order 1.5 yards ready-mix
Two-car Driveway 20' × 20' (6 inches)
Cubic yards:7.4 yards
Requires 6-inch minimum for vehicle traffic
Order 8 yards ready-mix
50-foot Sidewalk (4' wide, 4 inches thick)
Cubic yards:2.47 yards
80 lb bags:111 bags
Order 2.75 yards ready-mix
Four 12-inch Diameter Deck Posts (4 feet deep)
Cubic yards:0.47 yards
80 lb bags:21 bags
Bagged concrete practical
💪 Concrete Strength Specifications
PSI Ratings (ACI 318)
2,500
PSI
Residential footings, patios
3,000
PSI
Residential slabs, driveways
(Most common)
(Most common)
3,500
PSI
Floors with heavy loads
4,000
PSI
Commercial, high-traffic areas
Standard residential mix: 3,000 PSI with 5-6 inch slump
👷 Professional Standards
🕐Curing Requirements (ACI 308)
- 7Minimum 7 days moist curing for full strength
- 24Avoid foot traffic for 24 hours
- ✓Full weight-bearing after 7 days
- 28Maximum strength achieved at 28 days
🌡️Temperature Requirements
Minimum pour temp40°F
Maximum pour temp95°F
❄️Cold weather - Concrete must be minimum 65°F during mixing (ACI 306): Use heated mix and insulating blankets
☀️Hot weather (>85°F): Use retarders, shade, and fog misting
📚 Building Code References
•ACI 318: Structural Concrete Code
•ACI 301: Concrete Specifications
•ACI 308: Curing Requirements
•IRC R506: Concrete Floor Requirements
•IBC 1905: Concrete Construction Standards
•ASTM C150: Portland Cement Specifications
Always verify local requirements with your building department. Frost depths, seismic zones, and soil conditions affect specifications.
Calculate Your Concrete Materials
Get precise cubic yards, bags needed, and material estimates with industry-standard formulas.
Go to Concrete Calculator →