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Concrete Calculator

Calculate cubic yards and bags of concrete needed.

Last updated: June 13, 2026

Calculator

feet
feet
inches

Results

Cubic Yards1.23

33.3 cubic feet

60-lb Bags Needed75 bags
80-lb Bags Needed56 bags
Add 10% for waste1.36 cu yd

Recommended order amount

How to Use This Calculator

  1. 1Enter the length of your project area in feet.
  2. 2Enter the width in feet.
  3. 3Enter the depth or thickness in inches.
  4. 4View cubic yards needed and bag counts for 60-lb and 80-lb bags.

Formula Explanation

Concrete volume is calculated by multiplying length × width × depth and converting to cubic yards. Add 10% extra to account for waste and spillage.

Volume (cu ft) = Length(ft) × Width(ft) × Depth(in) / 12 Cubic Yards = Volume / 27 60-lb bags = Volume / 0.45 80-lb bags = Volume / 0.60

Variables:

LengthProject length in feet
WidthProject width in feet
DepthConcrete thickness in inches (typical: 4" for slabs)

Worked Examples

10×10 ft patio, 4 inches deep

  1. 1. Volume = 10 × 10 × (4/12) = 33.33 cu ft
  2. 2. Cubic yards = 33.33 / 27 = 1.23
  3. 3. 80-lb bags = 33.33 / 0.6 = 56 bags
Result: 1.23 cubic yards or 56 bags (80-lb)

20×30 ft driveway, 6 inches deep

  1. 1. Volume = 20 × 30 × (6/12) = 300 cu ft
  2. 2. Cubic yards = 300 / 27 = 11.11
  3. 3. Order: 11.11 × 1.10 = 12.22 yards (with waste)
Result: 11.11 cubic yards + 10% waste = 12.2 yards — order ready-mix

Why Use This Calculator

  • Avoid costly over-ordering or project-stopping under-ordering.
  • Instantly compare bag counts vs. ready-mix delivery.
  • Includes waste factor recommendation for real-world accuracy.
  • Works for any rectangular concrete project: slabs, footings, walls.
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Tips & Best Practices

  • Always order 10% more than calculated to account for uneven ground and spillage.
  • For projects over 2 cubic yards, ready-mix delivery is usually cheaper than bags.
  • Standard slab thickness is 4 inches for patios and 6 inches for driveways.
  • Prepare your forms and base before ordering — concrete does not wait.

Common Mistakes to Avoid

❌ Mixing up inches and feet for the depth measurement.

✅ Depth is almost always in inches (4–6"). Enter inches, not feet.

❌ Ordering exactly the calculated amount with no margin for waste.

✅ Add 10% to your order. Running short mid-pour creates weak joints.

❌ Not accounting for uneven ground that requires more concrete in low spots.

✅ Grade and level your base before calculating. Use the deepest point for depth.

Frequently Asked Questions

How much concrete do I need for a 10x10 slab?
A 10x10 foot slab at 4 inches thick requires about 1.23 cubic yards of concrete, or approximately 56 bags of 80-lb mix. Always order 10% extra for waste, bringing the total to about 1.36 cubic yards.
Should I use bags or ready-mix?
For projects under 1–2 cubic yards, bags are practical and allow you to work at your own pace. For larger projects, ready-mix truck delivery is more cost-effective and ensures consistent quality.
How thick should a concrete slab be?
Standard thicknesses: 4 inches for walkways and patios, 6 inches for driveways and garage floors, 8+ inches for foundations and heavy load areas. Always check local building codes.
What is the difference between 60-lb and 80-lb bags?
80-lb bags yield about 0.6 cubic feet of concrete; 60-lb bags yield about 0.45 cubic feet. 80-lb bags are more cost-effective per volume but heavier to handle.
How long does concrete take to cure?
Concrete reaches initial set in 24–48 hours, is walkable in 24 hours, and reaches full strength (about 4,000 PSI) in 28 days. Keep it moist for the first 7 days for best results.
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