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Concrete Calculator
Calculate how much concrete you need for any slab, footing, or column. Get cubic yards, cubic feet, bag counts, and cost estimates instantly.
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Concrete Calculator
How to Use the Concrete Calculator
- Select the shape — Choose Slab (most common), Footing, or Column.
- Enter dimensions — Input length, width, and thickness/depth. Switch between imperial and metric as needed.
- Click Calculate — Get cubic yards, cubic feet, bag counts for 40/60/80 lb bags, and a cost estimate.
- Add 10% for waste — The calculator reminds you, but always order slightly more than calculated.
Concrete Calculator Formula
The basic formula for a concrete slab is:
Volume (ft³) = Length (ft) × Width (ft) × Depth (ft)
Volume (yd³) = Volume (ft³) ÷ 27
Volume (yd³) = Volume (ft³) ÷ 27
For a column or cylinder:
Volume (ft³) = π × Radius² × Height
Concrete Coverage Reference Table
| Thickness | 1 Cubic Yard Covers | 60 lb Bags per Yard |
|---|---|---|
| 3 inches | 108 sq ft | 60 bags |
| 4 inches | 81 sq ft | 45 bags |
| 6 inches | 54 sq ft | 60 bags |
| 8 inches | 40.5 sq ft | 80 bags |
| 12 inches | 27 sq ft | 90 bags |
Ready-Mix vs. Pre-Mixed Bags
The choice between ready-mix concrete and pre-mixed bags depends primarily on project size:
- Pre-mixed bags — Best for projects under 1 cubic yard. No minimum order, flexible schedule, easy for DIY. Each 60 lb bag yields approximately 0.45 cubic feet.
- Ready-mix (truck delivery) — Best for projects over 1 yard. More cost-effective per yard, better consistency. Minimum orders typically 1–2 yards. Requires you to be ready to pour immediately on delivery.
Standard Concrete Slab Thickness Guidelines
| Application | Recommended Thickness | Notes |
|---|---|---|
| Sidewalk / Walkway | 3–4 inches | Foot traffic only |
| Patio | 4 inches | Furniture + foot traffic |
| Driveway (passenger cars) | 4 inches | Minimum per code |
| Driveway (trucks/RVs) | 5–6 inches | Add rebar or wire mesh |
| Garage floor | 4–6 inches | With rebar recommended |
| Footing / Foundation | 8–12 inches | Per local building code |
Tips for a Successful Concrete Pour
- Always pour over a compacted gravel base (4–6 inches) to prevent settling and cracking.
- Use rebar or wire mesh reinforcement for slabs over 50 sq ft or any driveway.
- Cure concrete slowly — keep it moist for at least 7 days for maximum strength.
- Don't pour when temperature is below 40°F or above 90°F without special precautions.
- Control joints should be cut every 8–12 feet to manage cracking.
? Frequently Asked Questions
How many bags of concrete do I need for a 10×10 slab at 4 inches thick?
A 10×10 slab at 4 inches thick requires approximately 1.23 cubic yards of concrete. That equals roughly 82 bags of 60 lb pre-mixed concrete, or about 61 bags of 80 lb bags. Always add 10% for waste, so plan for 90 bags (60 lb) or 67 bags (80 lb).
What is the difference between cubic yards and cubic feet for concrete?
One cubic yard equals 27 cubic feet. Ready-mix concrete is ordered in cubic yards, while smaller projects and pre-mixed bags are calculated in cubic feet. Our calculator shows both automatically so you can order either way.
How thick should a concrete slab be?
For residential driveways: 4 inches minimum. Garage floors: 4–6 inches. Sidewalks and patios: 3–4 inches. Footings below frost line: typically 8–12 inches wide and 8 inches deep, depending on local code. Always consult your local building code.
What does a yard of concrete cost?
Ready-mix concrete typically costs $110–$165 per cubic yard delivered. Prices vary by location, mix design, and current material costs. Pre-mixed bags (60 lb) cost about $5–7 each at big-box stores. For large pours, ready-mix is almost always more cost-effective.
Should I add extra concrete to my order?
Yes — always add 10% to your calculated volume to account for uneven subgrades, spillage, and slight variations in forms. For complex pours with lots of edges or corners, consider 15%. Running short mid-pour is a costly problem.
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💡 Pro Tips
- ✅ Always add 10% to your calculated volume for waste
- ✅ Pour over a compacted gravel base
- ✅ Use rebar for slabs over 50 sq ft
- ✅ Cure for 7+ days before heavy use
- ✅ Don't pour below 40°F