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 a clear bagged vs. ready-mix truck recommendation — in seconds, no signup.
Professional Concrete Calculator
Industry-standard material calculations based on ACI, IBC/IRC, and DOT specifications.
Project Type
Multiple areas or depths? Total the volume →
Dimensions
See what goes under a slab — and why thickness matters
See where to cut control joints so the slab doesn’t crack randomly
Specifications
Residential driveways, garage floors, standard slabs
See how cubic yards convert to 60- and 80-lb bags — and when to order ready-mix
Pouring concrete that lasts
The volume math is only half the job. These engineering-style diagrams cover the three things the numbers don’t show: how a cubic yard converts to 60- and 80-lb bags (and when to order a ready-mix truck instead), what layers go under a slab, and where to cut control joints so the concrete cracks where you want it to. Use the “see the diagram” links beside the inputs above to jump to the figure you need.
The bags-per-yard diagram is why the calculator shows both a bag count and a ready-mix volume. A cubic yard is twenty-seven cubic feet, and each bag yields only a fraction of that, so bag counts climb fast — past roughly a half yard, ordering a truck beats mixing bags by hand. The estimate gives you the crossover so you order the right way, not just the right amount.
The slab section explains why a slab estimate is more than concrete volume. A proper slab sits on a compacted gravel sub-base over a vapor barrier, with the steel held at mid-depth on chairs where it actually resists cracking. Those layers are separate materials the calculator accounts for, and the reinforcement only works if it is lifted off the ground.
The control-joint comparison is why the calculator spaces joints off the slab thickness. Concrete shrinks and will crack; control joints decide where by giving the crack a straight line to follow, spaced in feet at roughly two to three times the slab thickness in inches and cut early. Skip them and the slab still cracks — just wherever it wants.
▶ Watch: How to Calculate Concrete (Slabs, Footings & Posts)
Calculation Formulas
Concrete is sold by cubic yard. We multiply dimensions in feet, then divide by 27 (cubic feet per cubic yard).
Example:
10ft × 10ft × 0.33ft (4 inches) = 33 cubic feet ÷ 27 = 1.22 cubic yards
Each 80lb bag yields 0.6 cubic feet. There are 45 bags per cubic yard (27 ÷ 0.6).
Example:
1.22 yd³ × 45 = 55 bags (80lb)
Each 60lb bag yields 0.45 cubic feet. There are 60 bags per cubic yard (27 ÷ 0.45).
Example:
1.22 yd³ × 60 = 73 bags (60lb)
Waste factors account for spillage, irregular shapes, and over-excavation. Varies by project type.
Example:
1.22 yd³ × 1.05 (5% waste) = 1.28 cubic yards total
Standard Constants
| Constant | Value | Description |
|---|---|---|
| Cubic Feet per Yard | 27 | Standard conversion: 3ft × 3ft × 3ft |
| 80lb Bag Yield | 0.60 ft³ | Per manufacturer specifications (Quikrete, Sakrete) |
| 60lb Bag Yield | 0.45 ft³ | Per manufacturer specifications |
| Slab Waste Factor | 5% | Industry standard for simple rectangular slabs |
| Footing Waste Factor | 10% | Higher due to irregular excavation |
| Post Hole Waste Factor | 7.5% | Accounts for depth variation and spillage |
Note: All calculations include appropriate waste factors based on project complexity and material type. Results are estimates and should be verified by professionals before purchasing materials.
ACI 318 - Building Code Requirements for Structural Concrete(ACI 318-19)
View StandardProvides comprehensive standards for concrete design, construction, and inspection. Covers mix design requirements, reinforcement specifications, formwork standards, and construction practices for structural concrete.
Key Requirements:
- •Minimum 28-day compressive strength: 2,500-5,000 PSI based on application
- •Concrete cover requirements: 2" minimum for slabs on grade, 3" for exposed concrete
- •Maximum water-cement ratio: 0.45 for exterior exposure, 0.50 for interior
International Residential Code (IRC) - Section R403(IRC 2021)
View StandardGoverns residential foundation and footing requirements. Specifies minimum footing dimensions, depth below frost line, and concrete strength requirements for residential construction.
Key Requirements:
- •Footings must extend minimum 12" below undisturbed ground
- •Footings must be below frost line (varies by region)
- •Minimum footing width: 12" for one-story, 15" for two-story
- •Minimum concrete strength: 2,500 PSI
ASTM C94 - Ready-Mixed Concrete Specifications(ASTM C94/C94M)
View StandardDefines requirements for ready-mixed concrete including materials, production, delivery, and testing. Ensures consistency and quality control in commercial concrete supply.
Key Requirements:
- •Maximum delivery time: 90 minutes from batching
- •Maximum 300 drum revolutions during transport
- •Slump testing required before discharge
- •Temperature limits: 50-90°F at placement
Department of Transportation (DOT) Concrete Specifications(Varies by State DOT)
State-specific requirements for concrete used in transportation infrastructure. Generally requires higher strength concrete (4,000-5,000 PSI) and specific air entrainment for freeze-thaw resistance.
Key Requirements:
- •Typical minimum strength: 4,000 PSI for roadways
- •Air entrainment: 5-8% for freeze-thaw protection
- •Specific aggregate gradations and maximum sizes
Standards Disclaimer: Standards and codes are subject to periodic updates. Always verify current requirements with local building authorities and professional engineers before beginning construction. Links provided are for reference only.
Frost Line Depth Requirements
IRC R403.1.4 - Footings must extend below frost line
Frost line depth varies dramatically across the United States. Footings and posts must extend below this depth to prevent heaving from freeze-thaw cycles.
Regional Examples:
Concrete Strength Requirements by Climate
Varies by freeze-thaw exposure and local codes
Minimum PSI ratings vary based on climate exposure. Colder climates require higher strength concrete and air entrainment for durability.
Regional Examples:
Seismic Design Requirements
IRC R403.1.7 & IBC 1808 - Varies by Seismic Design Category
Earthquake-prone regions have additional reinforcement requirements for foundation concrete. Seismic Design Categories range from A (low risk) to E (high risk).
Regional Examples:
Slab Thickness Requirements
Varies by building department and use case
While IRC specifies minimum 3.5" for residential slabs, many jurisdictions require 4" minimum. Commercial and heavy-load applications require thicker slabs.
Regional Examples:
Permit Requirements
Local jurisdiction regulations vary
Permit requirements and inspection schedules vary by municipality. Some areas require permits for any concrete work, others only for structural elements.
Regional Examples:
Before You Build
- •Contact your local building department for specific requirements
- •Verify frost line depths, wind zones, and seismic requirements for your area
- •Check if permits are required and schedule required inspections
- •Consult with a local contractor familiar with local codes
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)
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🚛 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
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Want to Learn More?
What actually decides concrete strength — the water-cement ratio, ACI cold and hot weather rules, air entrainment, admixtures, fibers, and base prep.
Read the Concrete Strength
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.