Concrete Calculator
Calculate exactly how much concrete you need in cubic yards or bags. Works for slabs, driveways, patios, footings, columns, and stairs. Get instant cost estimates and mix quantities.
How much concrete do I need?
To calculate concrete for a rectangular slab, measure length × width × thickness (all in feet), then divide by 27 to get cubic yards. One cubic yard equals 27 cubic feet.
- Formula: (Length × Width × Thickness) ÷ 27 = Cubic Yards
- Bags per yard: ~45 bags (80-lb) or ~60 bags (60-lb) per cubic yard
- Coverage: 1 cubic yard covers 81 sq ft at 4" thick, 54 sq ft at 6" thick
You need approximately 2.47 cubic yards of concrete. We recommend ordering 2.75 cubic yards (+10%) to account for waste and spillage.
Your footing requires approximately 1.23 cubic yards of concrete.
Your 4 columns require approximately 0.12 cubic yards of concrete total.
You need 45 bags of 80-lb concrete mix. We recommend buying 50 bags (+10% overage).
📊 Bags Per Cubic Yard Reference
| Bag Size | Yield per Bag | Bags per Cubic Yard | Bags per Cubic Foot |
|---|---|---|---|
| 80 lb | 0.60 ft³ | 45 bags | 1.67 bags |
| 60 lb | 0.45 ft³ | 60 bags | 2.22 bags |
| 50 lb | 0.375 ft³ | 72 bags | 2.67 bags |
| 40 lb | 0.30 ft³ | 90 bags | 3.33 bags |
Tip: For projects requiring more than 1 cubic yard, ready-mix delivery is often more cost-effective than bagged concrete.
📖 How to Use This Calculator
Select your project type
Choose "Slab/Patio" for flat surfaces, "Footing/Wall" for foundations, "Column/Tube" for round piers, or "Bags Calculator" to estimate bagged concrete needs.
Enter your measurements
Input the length, width, and thickness (or height). You can use feet, inches, meters, or centimeters – the calculator converts automatically.
Add price for cost estimate
Enter the price per cubic yard (typically $125-$150 for ready-mix) to get an estimated project cost.
Review results with overage
Results show cubic yards, cubic feet, and bags needed. The calculator automatically adds 10% overage for waste, spillage, and uneven subgrade.
🧱 What is Concrete & How is it Measured?
Concrete is a composite material made from cement, aggregate (gravel and sand), and water. When mixed together, a chemical reaction called hydration causes the cement to harden and bind the aggregates into a stone-like mass. Ready-mix concrete is sold by volume, typically measured in cubic yards in the United States.
📌 Key Volume Conversions
- 1 cubic yard = 27 cubic feet
- 1 cubic yard = 46,656 cubic inches
- 1 cubic yard ≈ 0.765 cubic meters
- 1 cubic yard of concrete ≈ 4,000 lbs (2 tons)
- 1 cubic yard ≈ 45 bags of 80-lb concrete mix
Understanding Cubic Yards
A cubic yard is a unit of volume that represents a cube measuring 3 feet on each side (3 ft × 3 ft × 3 ft = 27 cubic feet). Visualizing this helps when ordering:
Physical Size
One cubic yard is roughly the size of a standard washing machine and dryer stacked together.
Truck Capacity
A standard concrete truck holds 8-10 cubic yards. Most suppliers have minimum delivery requirements of 1-3 yards.
Weight
One cubic yard of concrete weighs approximately 4,000 lbs. Plan accordingly for structural support.
Coverage
1 cubic yard covers 81 sq ft at 4" thick, 54 sq ft at 6" thick, or 27 sq ft at 12" thick.
🔢 How to Calculate Concrete (Formula)
Calculating concrete is straightforward once you understand the formula. The key is ensuring all measurements are in the same units (usually feet) before multiplying.
Standard Concrete Formula
Where length, width, and thickness are all in feet.
When Thickness is in Inches
Divide inches by 12 to convert to feet before calculating.
Step-by-Step Calculation
💡 Example: Driveway Concrete Calculation
Problem: Calculate concrete for a 20 ft × 10 ft driveway, 5 inches thick
- Step 1: Convert inches to feet: 5 ÷ 12 = 0.417 feet
- Step 2: Calculate cubic feet: 20 × 10 × 0.417 = 83.4 cubic feet
- Step 3: Convert to cubic yards: 83.4 ÷ 27 = 3.09 cubic yards
- Step 4: Add 10% overage: 3.09 × 1.10 = 3.4 cubic yards to order
🔵 Coverage at 4" Thick
1 cubic yard covers:
81 square feet
Standard for patios, sidewalks
🟢 Coverage at 6" Thick
1 cubic yard covers:
54 square feet
Standard for driveways
📏 Concrete Thickness Guide by Project Type
Choosing the correct concrete thickness is crucial for durability and structural integrity. Here are the recommended thicknesses for common projects:
| Project Type | Minimum Thickness | Recommended | Reinforcement |
|---|---|---|---|
| Sidewalks | 4 inches | 4 inches | Wire mesh or fiber |
| Patios | 4 inches | 4 inches | Wire mesh optional |
| Driveways (cars) | 4 inches | 5-6 inches | Wire mesh + rebar |
| Driveways (trucks/RVs) | 5 inches | 6-8 inches | Rebar grid |
| Garage floors | 4 inches | 5-6 inches | Wire mesh + rebar |
| Shed foundation | 4 inches | 4-6 inches | Wire mesh |
| Pool deck | 4 inches | 4 inches | Wire mesh |
| Footings | 8 inches | 12+ inches | Rebar required |
| Foundation walls | 8 inches | 8-12 inches | Rebar required |
| Commercial (heavy loads) | 6 inches | 8+ inches | Rebar grid |
⚠️ Thickness Matters
Don't skimp on thickness to save money – it will cost more in the long run:
- Thin concrete cracks under stress and heaving
- Adding 1" of thickness increases strength significantly
- Proper base preparation is as important as thickness
- Always check local building codes for minimum requirements
💰 Concrete Cost Guide (2026 Prices)
Understanding concrete costs helps you budget accurately. Prices vary by location, mix design, and order quantity.
Ready-Mix Concrete Pricing
| Mix Type | Price per Cubic Yard | Common Uses |
|---|---|---|
| Standard Mix (3000 PSI) | $125 - $145 | Footings, general slabs |
| Standard Mix (4000 PSI) | $135 - $155 | Driveways, garage floors |
| High-Strength (5000+ PSI) | $150 - $180 | Commercial, structural |
| Fiber-Reinforced | $145 - $165 | Crack-resistant slabs |
| Colored Concrete | $160 - $200+ | Decorative applications |
| Stamped/Decorative | $200 - $300+ | Patios, walkways |
Additional Costs to Consider
Delivery Fees
$50-$100 delivery fee. Additional charges may apply for distances over 20 miles.
Short Load Fee
$50-$100 per yard for orders under minimum (typically 3-5 yards).
Overtime Charges
$2-$4 per minute if truck waits over 5-7 minutes per yard.
Weekend/Holiday
10-20% premium for Saturday delivery. Sunday usually unavailable.
💡 Cost-Saving Tips
- Order full loads: Trucks typically hold 8-10 yards – full loads cost less per yard
- Be ready: Have forms, base, and crew ready to avoid overtime charges
- Combine orders: Coordinate with neighbors for better pricing
- Weekday delivery: Avoid Saturday/rush delivery fees
- Compare suppliers: Get 3+ quotes – prices vary significantly
📦 Bags vs. Ready-Mix: Which Should You Choose?
Deciding between bagged concrete and ready-mix delivery depends on your project size, budget, and convenience preferences.
📦 Bagged Concrete
- Best for: Under 1 cubic yard
- Cost: $5-8 per 80-lb bag
- Pros: DIY-friendly, no minimum, mix as needed
- Cons: Labor-intensive, inconsistent mix quality
- Projects: Fence posts, small repairs, stepping stones
🚚 Ready-Mix Delivery
- Best for: Over 1 cubic yard
- Cost: $125-150 per cubic yard
- Pros: Consistent quality, saves time, less labor
- Cons: Minimum order, time pressure
- Projects: Driveways, patios, foundations
Cost Comparison
| Volume | 80-lb Bags Needed | Bags Cost (~$6.50 each) | Ready-Mix Cost | Winner |
|---|---|---|---|---|
| 0.25 yd³ | 12 bags | $78 | $200+ (min order) | ✅ Bags |
| 0.50 yd³ | 23 bags | $150 | $200+ (min order) | ✅ Bags |
| 1.00 yd³ | 45 bags | $293 | $175-200 | ✅ Ready-Mix |
| 2.00 yd³ | 90 bags | $585 | $300-350 | ✅ Ready-Mix |
| 5.00 yd³ | 225 bags | $1,463 | $700-800 | ✅ Ready-Mix |
📌 The Breakeven Point
Ready-mix becomes more cost-effective at approximately 0.75-1 cubic yard. Beyond cost, consider the labor savings – mixing 45+ bags of concrete by hand is exhausting and time-consuming.
🔬 Concrete Mix Ratios & Strength (PSI)
The strength of concrete is measured in PSI (pounds per square inch) and depends on the mix ratio of cement, sand, and aggregate. Here's what you need to know:
| PSI Rating | Mix Ratio (Cement:Sand:Gravel) | Recommended Uses |
|---|---|---|
| 2500 PSI | 1:3:5 | Non-structural, footings, mass concrete |
| 3000 PSI | 1:2.5:4 | Sidewalks, patios, floor slabs |
| 3500 PSI | 1:2:3 | Driveways, garage floors |
| 4000 PSI | 1:2:2.5 | Heavy-duty driveways, commercial |
| 4500 PSI | 1:1.5:2 | Structural, high-load areas |
| 5000+ PSI | Special mix | Commercial, industrial, bridges |
📌 Standard Residential Mix
Most residential projects use 3000-4000 PSI concrete. A 3500 PSI mix is a good all-purpose choice for driveways and garage floors. Always specify the PSI when ordering ready-mix.
Understanding Concrete Curing
Concrete doesn't dry – it cures through a chemical reaction. Proper curing is essential for achieving full strength:
- 24 hours: Concrete sets but is not walkable
- 48 hours: Light foot traffic okay
- 7 days: Reaches ~70% of final strength
- 28 days: Reaches full design strength (100% PSI rating)
🏗️ Common Concrete Project Estimates
Here are typical concrete requirements for common residential projects to help you plan:
Flat Work (Slabs, Patios, Driveways)
| Project Type | Typical Size | Thickness | Cubic Yards |
|---|---|---|---|
| Small patio | 10 × 10 ft | 4 inches | 1.25 yd³ |
| Medium patio | 12 × 16 ft | 4 inches | 2.40 yd³ |
| Large patio | 20 × 20 ft | 4 inches | 5.00 yd³ |
| Sidewalk (4 ft wide × 25 ft) | 100 sq ft | 4 inches | 1.25 yd³ |
| Single-car driveway | 10 × 20 ft | 5 inches | 3.10 yd³ |
| Double-car driveway | 20 × 20 ft | 5 inches | 6.20 yd³ |
| Large driveway | 24 × 40 ft | 6 inches | 17.80 yd³ |
| One-car garage floor | 12 × 20 ft | 5 inches | 3.70 yd³ |
| Two-car garage floor | 24 × 24 ft | 5 inches | 8.90 yd³ |
Footings & Foundations
| Project Type | Dimensions | Cubic Yards |
|---|---|---|
| Deck pier (12" dia × 48" deep) | Per pier | 0.12 yd³ |
| Fence post hole (8" dia × 24" deep) | Per hole | 0.03 yd³ |
| Strip footing (100 linear ft) | 12" × 8" | 2.50 yd³ |
| Shed foundation | 10 × 12 ft × 4" | 1.50 yd³ |
| Hot tub pad | 10 × 10 ft × 6" | 1.85 yd³ |
⚠️ Always Order Extra
These estimates are for perfect conditions. Real-world factors that require additional concrete:
- Uneven subgrade requiring extra depth in spots
- Spillage and waste during pouring
- Form movement or blowouts
- Measurement errors
Recommendation: Add 5-10% to all calculations. Round up to the nearest quarter yard.
🔩 Concrete Reinforcement Guide
Reinforcement prevents cracking and adds tensile strength to concrete. Here's when and what type to use:
Wire Mesh
Best for slabs 4" or less. Common 6×6 W1.4/W1.4 mesh. Position at 1/3 depth from top.
Rebar (#4 or #5)
Required for driveways, footings, and structural elements. Space 12-18" on center both ways.
Fiber Reinforcement
Mixed directly into concrete. Good for crack control but doesn't replace structural rebar.
Control Joints
Not reinforcement, but essential. Space every 8-12 ft to control where concrete cracks.
When to Use What
| Application | Minimum Reinforcement | Recommended |
|---|---|---|
| Sidewalks | None required | Wire mesh or fiber |
| Patios | None required | Wire mesh |
| Residential driveways | Wire mesh | Wire mesh + #4 rebar |
| Garage floors | Wire mesh | #4 rebar 18" OC |
| Footings | #4 rebar continuous | #5 rebar with ties |
| Foundation walls | #4 rebar both ways | Per engineer spec |
❌ 8 Common Concrete Mistakes to Avoid
Avoid these costly errors that can ruin your concrete project:
Adding Too Much Water
Extra water makes concrete easier to work but dramatically weakens it. Never add water to ready-mix at the job site.
Pouring in Wrong Weather
Concrete shouldn't be poured when temps are below 40°F or above 90°F without special precautions.
Inadequate Thickness
Saving money with thinner concrete leads to early cracking and failure. Follow thickness guidelines.
Poor Base Preparation
Concrete is only as good as its base. Compact subgrade properly and use 4" of gravel.
Skipping Control Joints
Without joints, concrete will crack randomly. Cut or tool joints every 8-12 feet.
Improper Curing
Concrete needs moisture to cure properly. Cover or spray with curing compound for 7 days minimum.
Ordering Too Little
Running short means a visible cold joint or waiting for another truck. Always order 5-10% extra.
Not Being Ready
Concrete trucks charge overtime. Have forms, tools, and enough workers ready before the truck arrives.
✅ Expert Tips & Best Practices
Before Ordering
- Measure twice, calculate once – verify all dimensions before calling
- Know your PSI requirements for the application
- Ask about delivery schedules and minimum order requirements
- Confirm access – trucks are large and heavy
Day of Pour
- Have forms set, stakes secure, and base compacted the day before
- Pre-wet dry subgrade to prevent it from sucking moisture from concrete
- Position concrete directly from chute when possible
- Have enough workers – you'll need 1 person per cubic yard minimum
Finishing
- Don't over-work the surface – brings excess water up
- Wait for bleed water to evaporate before final finish
- Cut control joints within 6-12 hours of pour
- Apply curing compound immediately after finishing
This calculator provides estimates for planning purposes. Always verify calculations with your concrete supplier before ordering.
📚 Sources & References
- Concrete Network - Industry Resource
- Quikrete - Concrete Products Guide
- American Concrete Institute (ACI) Building Code Requirements
- Portland Cement Association Design Guidelines
❓ People Also Ask
How many bags of concrete do I need for a 10×10 slab?
For a 10×10 ft slab at 4 inches thick, you need approximately 1.25 cubic yards or about 56 bags of 80-lb concrete mix. At 6 inches thick, you'd need 1.85 cubic yards or 83 bags. We recommend buying 10% extra.
How much does a yard of concrete weigh?
One cubic yard of concrete weighs approximately 4,000 pounds (2 tons). This includes the cement, aggregate (gravel), sand, and water. Lightweight concrete mixes weigh less, around 2,800-3,000 lbs per yard.
How many 80-lb bags of concrete make a yard?
You need approximately 45 bags of 80-lb concrete to make one cubic yard. Each 80-lb bag yields about 0.6 cubic feet. For 60-lb bags, you'd need about 60 bags per cubic yard.
How thick should a concrete driveway be?
A residential driveway should be 5-6 inches thick for cars and light trucks. For heavier vehicles (RVs, boats), increase to 6-8 inches. Always use wire mesh or rebar reinforcement and a proper gravel base.
How much does a concrete driveway cost?
A concrete driveway costs approximately $8-$18 per square foot installed, or $4,000-$10,000+ for a typical two-car driveway. Costs include concrete ($125-150/yd³), labor ($3-8/sq ft), base prep, forms, and finishing.
Can I pour concrete over old concrete?
Yes, but the old concrete must be clean, structurally sound, and properly prepared. Apply bonding agent, ensure minimum 2" overlay thickness, and address any cracks first. In many cases, removal is the better long-term choice.
📋 Frequently Asked Questions
Most ready-mix suppliers have a minimum delivery of 1-3 cubic yards. Orders below the "full load" (typically 8-10 yards) often incur a short-load fee of $50-100 per yard under the minimum. For very small jobs, bagged concrete may be more economical.
Concrete reaches approximately 70% strength in 7 days and full design strength (100%) in 28 days. Light foot traffic is okay after 48 hours, vehicles after 7 days, and heavy loads after 28 days. Always keep concrete moist during the first 7 days for proper curing.
3000 PSI is standard for sidewalks and patios. 3500-4000 PSI is recommended for driveways and garage floors. 4500+ PSI is used for commercial and structural applications. When in doubt, go with 4000 PSI – the extra strength costs only $10-15 more per yard.
Wire mesh is typically adequate for sidewalks and patios. Rebar is recommended for driveways (especially with vehicle traffic), garage floors, and any structural application. For residential driveways, #4 rebar on 18" centers both ways is standard. Always check local building codes.
Small projects using bagged concrete are very DIY-friendly. For ready-mix delivery, experience helps significantly – you'll have limited time to place, spread, and finish before the concrete sets. Consider hiring help for anything over 2 cubic yards. Proper preparation (forms, base, tools) is key to success.
Standard recommendation is 4-6 inches of compacted gravel (crushed stone or road base) over undisturbed or compacted soil. Sand alone is not recommended. The base should be level and thoroughly compacted. Good drainage beneath the slab prevents frost heaving.
Calculate each step as a rectangular section. Multiply width × depth (run) × height (rise) for each step, then add the platform. Most steps are 7" rise × 11" run. For example, 3 steps plus platform (3 ft × 4 ft): calculate each layer's volume and sum them. Our calculator handles this automatically.
The ideal temperature range is 50-75°F (10-24°C). Spring and fall are typically best. Avoid pouring when temperatures will drop below 40°F within 24 hours or exceed 90°F. Early morning pours work well in summer. In cold weather, use heated enclosures and blankets.
Order 5-10% extra concrete. For well-prepared sites with accurate measurements, 5% is sufficient. For rough grade, irregular shapes, or less experienced crews, go with 10%. Remember: having 1/4 yard left over is far better than coming up short and creating a cold joint.
Divide cubic feet by 27 to get cubic yards. One cubic yard equals 27 cubic feet (3 ft × 3 ft × 3 ft = 27 ft³). For example, 81 cubic feet ÷ 27 = 3 cubic yards. Our calculator handles all conversions automatically.