Concrete Calculator
How much concrete do you actually need? This free concrete calculator gives DIY homeowners and remodeling pros instant cubic-yard, 60 lb bag, and 80 lb bag counts for slabs, driveways, footings, post holes, stairs, walls, and columns — all from one form.
Concrete mistakes are expensive. Order too little and your pour stops mid-job; order too much and you pay short-load fees plus disposal. A small math error on a 4-inch slab can leave you 3 bags short or 6 bags over — every single time.
Built-in ACI 318 waste factor, support for ready-mix and bagged products, and side-by-side bagged vs. truck-delivery cost — in seconds, no signup.
Professional Concrete Calculator
Industry-standard material calculations based on ACI, IBC/IRC, and DOT specifications.
Project Type
Dimensions
Specifications
Residential driveways, garage floors, standard slabs
▶ Watch: How to Calculate Concrete (Slabs, Footings & Posts)
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.
📊 Concrete Volume by Project Type
Standard Slab (4")
Driveway (6")
Footings (12" deep)
Posts (12" diameter)
📐 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)
🧮 Step-by-Step Calculation
Example: 10' × 20' Patio Slab (4 inches thick)
🚛 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
📋 Common Concrete Projects
10' × 10' Patio (4 inches)
Two-car Driveway 20' × 20' (6 inches)
50-foot Sidewalk (4' wide, 4 inches thick)
Four 12-inch Diameter Deck Posts (4 feet deep)
💪 Concrete Strength Specifications
PSI Ratings (ACI 318)
(Most common)
👷 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
📚 Building Code References
Heavy material — watch the weight limit
Concrete, brick, and masonry hit tonnage caps fast. Most dumpsters cap heavy material at 10 tons, and overage fees stack quickly. See the disposal guide before you load.
Read the heavy-debris guide →
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Related Code Guides
Building code, climate zone, and standards references that change defaults for this calculator.
Climate Zone 3: R-Value Requirements (2021 IECC)
Warm Climate Zone 3 R-value minimums for the Carolinas, Georgia, central Texas, Arizona, and the Mid-South under the 2021 IECC.
Climate Zone 4: R-Value Requirements (2021 IECC)
Mixed-humid Climate Zone 4 R-value minimums for the Mid-Atlantic, Ohio Valley, Kentucky, Tennessee, and northern Texas under the 2021 IECC.
Climate Zone 8: R-Value Requirements (2021 IECC)
Subarctic Climate Zone 8 R-value minimums for most of Alaska under the 2021 IECC and Alaska Building Energy Efficiency Standard.
Frequently Asked Questions
What is a cubic yard of concrete?
A cubic yard is 27 cubic feet of concrete (3 feet × 3 feet × 3 feet). This is the standard measurement for ready-mix concrete delivery. One cubic yard weighs approximately 4,000 pounds and covers 81 square feet at 4 inches thick.
How many 80-lb bags of concrete do I need per cubic yard?
Each 80-lb bag yields approximately 0.6 cubic feet when mixed. One cubic yard requires 45 bags of 80-lb concrete mix. For 60-lb bags, which yield 0.45 cubic feet each, you need 60 bags per cubic yard.
What thickness should a concrete slab be?
IRC code requires 3.5 inches minimum for residential slabs-on-grade. Standard practice is 4 inches for garage floors, patios, and basement slabs. Driveways carrying passenger vehicles need 4-5 inches, increasing to 6 inches for RV and heavy truck traffic. Always verify local building code requirements.
Why add waste factor to concrete calculations?
ACI recommends 5-10% waste factor for spillage, over-excavation, uneven subgrade, and form irregularities. Simple rectangular slabs typically need 5-7% extra. Complex pours with multiple sections, steps, or difficult access require 10-15% waste factor.