Free Landscape Calculator
Concrete Calculator
Calculate exactly how many cubic yards and 80lb bags of concrete you need for slabs, driveways, patios and footings. Instant results with ready-mix and bag estimates.
👤 Who is this for: DIY slab pourers, contractors, fence-post setters & patio builders.
📊 Understanding Your Results
Cubic Yards — Standard unit for ready-mix concrete. Most companies have a 1 cubic yard minimum order.
80lb Bags — Each bag yields approximately 0.60 cubic feet. For small projects under 1 cubic yard, mixing bags yourself is practical.
Cost Estimate — Based on average US ready-mix prices of $100–$150 per cubic yard.
How the Concrete Calculator Works
Our concrete calculator uses standard volumetric calculations to estimate how much concrete you need for any slab, footing or structural pour.
The Concrete Formula
Step 2: Cubic Yards = Cubic Feet ÷ 27
Step 3: 80lb Bags = Cubic Yards × 45
Step 4: Add 10% for waste, spillage and thickness variations
Example: A 10×20 ft driveway at 6 inches = 200 × (6÷12) = 100 cu ft = 3.7 cubic yards. Add 10% — order 4.1 yards.
Recommended Concrete Thickness by Application
| Application | Thickness | Notes |
|---|---|---|
| Sidewalk / walkway | 4 inches | Foot traffic only |
| Residential patio | 4 inches | Foot traffic, furniture |
| Garage floor | 4–6 inches | Passenger vehicles |
| Residential driveway | 4–6 inches | Cars and light trucks |
| Heavy truck driveway | 6–8 inches | RV, delivery trucks |
📝 Real Project Example
10×10 ft slab, 4 inches thick:
- Area: 100 sq ft
- Volume: 100 × 0.333 = 33.3 cu ft
- Cubic yards: 33.3 ÷ 27 = 1.23 → order 1.5 cubic yards (ready-mix)
- Bags alternative: 33.3 ÷ 0.60 = 56 × 80-lb bags → 62 with 10% waste
- Weight: 1.23 × 2 = ~2.5 tons — plan delivery, not a pickup bed
- Cost check: 1.5 yd³ ready-mix at $150 = $225 + ~$120 delivery = ~$345 vs 62 bags at ~$6 = ~$372 — ready-mix wins at this size; bags win under ~1 cubic yard
For anything over a cubic yard, get at least one ready-mix quote before buying pallets of bags.
📚 Sources & Methodology
How we calculate. Step 1: volume in cubic feet = length × width × thickness (in feet). Step 2: cubic yards = cubic feet ÷ 27. Step 3: 80-lb bags = cubic feet ÷ 0.60 (per QUIKRETE published yield); 60-lb bags ÷ 0.45, 40-lb bags ÷ 0.30. We recommend adding 5–10% extra for spillage and uneven subgrade.
Cross-checked. Our bag yields match manufacturer technical data (80 lb = 0.60 cu ft → 45 bags per cubic yard), and our ~2 tons/yd³ weight figure matches published material-weight references (3,600–4,050 lbs).
Sources:
- ConcreteCalculate.com — Concrete Bag Calculator (bag yields per QUIKRETE technical data)
- The Calculator Site — How Much Does a Cubic Yard Weigh? (concrete 3,600–4,050 lbs per cubic yard)
Last updated: October 2026.
Frequently Asked Questions
Common questions about calculating concrete for slabs, driveways and patios.
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Never under-order — running short mid-pour creates cold joints that weaken the slab.
Order on weekdays — Saturday delivery costs $50–$100 extra.
Keep concrete moist for 7 days after pouring for maximum strength.