Concrete Calculator – Cubic Yards & Cost Estimator
Calculate exactly how much concrete you need for slabs, footings, driveways and post holes. Results in cubic yards (yd³), cubic feet, and number of bags (40/60/80 lb). Ready-mix vs. bagged concrete cost comparison included.
🧱 US Concrete Calculator
Enter dimensions in feet/inches. Volume calculated in cubic yards (yd³) with 10% waste included.
1. What are you pouring?
2. Dimensions
3. Concrete Strength (PSI)
4. Bag Size (for bagged concrete estimate)
Results
Includes 10% waste factor · Net volume: 1.48 yd³
How to Calculate Concrete in Cubic Yards – The Formula
The fundamental formula for calculating concrete volume in the US is simple but the units trip people up. Everything is measured in feet, and the result is in cubic feet (ft³). You then divide by 27 to convert to cubic yards (yd³) — the standard ordering unit for ready-mix.
📐 The Concrete Volume Formula
Always add 10% for waste, spillage and uneven subgrade. Our calculator does this automatically.
Worked Example: 12×10 ft Patio at 4″ Thick
Let's walk through the exact math for a standard backyard patio:
| Step 1: Get ft³ | 12 ft × 10 ft × (4 ÷ 12) = 12 × 10 × 0.333 = 40.0 ft³ |
| Step 2: Convert to yd³ | 40.0 ÷ 27 = 1.48 yd³ |
| Step 3: Add 10% waste | 1.48 × 1.10 = 1.63 yd³ |
| Step 4a: Bags (80 lb) | 1.63 yd³ × 45 bags/yd³ = 74 bags × $7.98 = ~$590 |
| Step 4b: Ready-mix | 1.63 yd³ × $130–$155/yd³ + $150 delivery = $362–$403 |
For this size project, ready-mix is actually cheaper than bags — and far less labor. Mixing 74 bags of concrete by hand takes 3–4 hours; a ready-mix truck delivers and you pour in 30 minutes.
How Many Bags Per Cubic Yard? (Exact Numbers)
This is the most-searched question about concrete in the US. Here are the exact figures based on manufacturer yield data from Quikrete and Sakrete:
| Bag Size | Yield per Bag | Bags per yd³ | Price (est. 2025) | Cost per yd³ (bags only) |
|---|---|---|---|---|
| 40 lb | ~0.30 ft³ | 90 | $4.48 | ~$403 |
| 60 lb | ~0.45 ft³ | 60 | $6.48 | ~$389 |
| 80 lb | ~0.60 ft³ | 45 | $7.98 | ~$359 |
PSI Guide – Which Strength for Which Project?
PSI (Pounds per Square Inch) measures how much compressive force a cured concrete slab can withstand. The right PSI depends on what you're building:
| PSI | Best For | European Equivalent | Notes |
|---|---|---|---|
| 2500 PSI | Sidewalks, light patios | ≈ C15/20 | Minimum for most residential use |
| 3000 PSI | Driveways, footings, foundations | ≈ C20/25 | Most common residential choice |
| 3500 PSI | Garage floors, high-traffic areas | ≈ C25/30 | Use in freeze-thaw climates |
| 4000 PSI | Load-bearing walls, columns | ≈ C25/30–C30/37 | Commercial grade; ask for air-entrained |
Slab Thickness Guide (Inches)
Thickness is the biggest variable that changes how much concrete you need. Going from 4″ to 6″ increases your concrete order by 50%:
| Thickness | yd³ per 100 sq ft | Use Case | Reinforcement Needed? |
|---|---|---|---|
| 3″ | 0.93 yd³ | Sidewalks, light patios | No (or wire mesh) |
| 4″ | 1.23 yd³ | Standard residential slab, garage floor | Wire mesh recommended |
| 5″ | 1.54 yd³ | Driveway (standard) | #3 rebar or mesh |
| 6″ | 1.85 yd³ | Heavy-duty driveway, RV pad | #3 or #4 rebar required |
| 8″ | 2.47 yd³ | Structural slabs, retaining walls | #4 rebar required |
Ready-Mix vs. Bagged Concrete – Which Should You Choose?
| Project Size | Recommendation | Why |
|---|---|---|
| < 0.3 yd³ (e.g., 2 fence posts) | Bags (fast-setting) | Quikrete 80-lb bags: just add water in the hole |
| 0.3–0.75 yd³ (small patio) | Bags or rented mixer | 14–34 bags of 80lb; manageable with a helper |
| 0.75–2 yd³ (garage slab) | Ready-mix truck | Saves hours of mixing; often costs less than bags |
| 2+ yd³ (foundation, driveway) | Ready-mix + pump if needed | The only practical option. Schedule a concrete pump if truck can't reach |
🚚 Ready-Mix Truck: What to Know Before You Order
- Minimum order: usually 1 yd³ (~$280–$400 depending on region)
- Short-load fee: if you order less than 10 yd³, expect a $50–$200 surcharge
- The truck must complete unloading in 90 minutes from the plant — after that, the concrete starts setting
- Have your crew and tools ready before the truck arrives. You can't pause the clock.
- Truck access: the mixer weighs 60,000+ lbs loaded. Check driveway clearance and turf.
Frost Line & Footing Depth by US Region
Footings must be placed below the frost line to prevent frost heave from cracking your foundation. The frost depth (maximum depth the ground freezes in winter) varies dramatically across the US:
| Region / States | Frost Depth | Min. Footing Depth |
|---|---|---|
| Deep South (FL, TX, LA, GA) | 0–6″ | 12″ (code minimum) |
| Mid-South (NC, TN, OK) | 6–12″ | 18″ |
| Mid-Atlantic (VA, MD, KY) | 12–24″ | 30″ |
| Northeast & Midwest (NY, OH, IL, IN) | 24–36″ | 42″ |
| Northern States (MN, WI, ND, MT) | 42–60″ | 60–66″ |
Always verify with your local building department — frost depths vary even within a state and local codes may require deeper footings than the frost line alone.
Frequently Asked Questions
How many cubic yards of concrete do I need for a 12×10 ft, 4" slab?↓
Volume = 12 × 10 × (4/12) = 40 ft³. Divided by 27 = 1.48 yd³. Add 10% waste → 1.63 yd³. You'd need about 74 bags of 80-lb concrete, or a small ready-mix delivery of ≈ 1.63 yd³.
How many bags of concrete make 1 cubic yard?↓
It depends on bag size: an 80-lb bag (e.g., Quikrete 5000) yields about 0.60 ft³, so you need 45 bags for 1 yd³. A 60-lb bag yields ~0.45 ft³ (60 bags/yd³). A 40-lb bag yields ~0.30 ft³ (90 bags/yd³). Always add 10% for waste.
What PSI concrete should I use for a driveway?↓
For a standard residential driveway, use 3000–3500 PSI. If you live in a freeze-thaw climate (northern states), specify 3500–4000 PSI with air-entrained mix – the tiny air bubbles protect against spalling when the ground freezes.
How thick should a concrete slab be?↓
Standard residential slabs (patios, walkways, garage floors): 4 inches. Driveways: 5–6 inches. Areas with heavy vehicles: 6 inches. Structural or commercial slabs: 6–8+ inches. Thicker slabs require rebar or wire mesh reinforcement.
When should I order ready-mix instead of buying bags?↓
Ready-mix becomes cost-effective above about 1 cubic yard (roughly 45 bags of 80 lb). Mixing more than that by hand or with a rented mixer is exhausting and time-consuming. Most ready-mix plants have a 1-yard minimum delivery, which currently runs $280–$400 depending on your region.
How deep should a footing be?↓
Footings must extend below the local frost line to prevent frost heave. Frost depth varies: southern states 0–12 inches, mid-Atlantic 24–30 inches, Midwest 36–48 inches, northern states up to 60 inches. Check your local building code — inspectors will verify footing depth before you pour.
Do I need rebar or wire mesh?↓
For driveways and slabs: #3 (3/8") rebar on a 24" grid or 6×6 W1.4×W1.4 wire mesh is standard. For footings: #4 (1/2") rebar, minimum two bars running the length. For posts/columns: no reinforcement is typically needed. Always check local codes.
What is the difference between PSI and MPa?↓
1 PSI ≈ 0.00689 MPa. The most common US residential concrete (3000 PSI) equals approximately 20.7 MPa, which is similar to the German/European C20/25 class. 4000 PSI ≈ 27.6 MPa ≈ C25/30 (European standard).