Free Concrete Calculator
Calculate exactly how much concrete you need in cubic yards and bags. Works for slabs, footings, walls, and columns.
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Concrete Needed
2.47 cubic yards
Cubic Feet
66.7 ft³
Cubic Meters
1.89 m³
60lb Bags
149
80lb Bags
112
Formula
Cubic Yards = (Length × Width × Depth in feet) ÷ 27 | 60lb bags ≈ Cubic Yards × 60 | 80lb bags ≈ Cubic Yards × 45How to Calculate Concrete Needed for Your Project
Getting the right amount of concrete is critical — too little means an incomplete pour that compromises structural integrity, and too much is wasted money. This calculator converts your slab dimensions (length, width, and depth) into cubic yards, the standard ordering unit for concrete, and also estimates the number of pre-mixed bags you'll need.
The formula is straightforward: multiply length × width × depth (all in feet) to get cubic feet, then divide by 27 to convert to cubic yards. Since depth is usually measured in inches, the calculator handles that conversion automatically.
Common Concrete Project Dimensions
- Sidewalk — typically 4 feet wide × 4 inches deep
- Patio — usually 4 inches deep on compacted gravel base
- Driveway — minimum 6 inches deep, 8 inches at the apron where it meets the street
- Footings — depth varies by frost line; typically 12-24 inches deep and 12-20 inches wide
- Fence posts — 10-inch diameter holes, 24-36 inches deep; about 1-2 bags per post
Tips for a Successful Concrete Pour
Preparation is everything with concrete. Before ordering, make sure your forms are secure, level, and properly braced. Use stakes every 2-3 feet on the outside of your forms. Place a 4-6 inch gravel base and compact it thoroughly — this prevents settling and cracking.
For slabs, use rebar or wire mesh for reinforcement. Place it in the lower third of the slab (use chairs or props to keep it off the ground). In cold climates, concrete should not be poured when temperatures are below 40°F unless you use accelerants and insulated blankets.
Concrete Cost Estimates
Ready-mix concrete costs $125-$175 per cubic yard delivered, depending on your location. A typical 10×20 foot patio (4 inches thick) needs about 2.5 cubic yards, costing $310-$440 for the concrete alone. Pre-mixed bags cost more per yard ($200-$250) but make sense for small jobs where delivery minimums apply. Budget an additional 20-30% for gravel base, rebar, forms, and tools.
Frequently Asked Questions
How many bags of concrete do I need for a 10×10 slab?
For a 10×10 foot slab at 4 inches thick, you need about 1.23 cubic yards. That's approximately 74 bags of 60lb mix or 56 bags of 80lb mix. For anything over 1 cubic yard, ordering ready-mix delivery is usually cheaper and easier.
How thick should a concrete slab be?
Standard slab thickness depends on use: 4 inches for patios, walkways, and shed floors; 6 inches for driveways and garage floors; 8+ inches for heavy equipment or commercial use. Always pour over 4-6 inches of compacted gravel base.
Should I order extra concrete?
Yes, always order 5-10% more than calculated. Concrete settles into uneven ground, forms may bow slightly, and you can't run short mid-pour. For ready-mix delivery, round up to the nearest half yard. Leftover concrete can be used for small projects or disposed of.
What's the difference between 60lb and 80lb concrete bags?
Both make the same strength concrete (typically 4,000 PSI). The 60lb bags are easier to handle and yield about 0.45 cubic feet each. The 80lb bags yield about 0.6 cubic feet and are more cost-effective per cubic foot but harder on your back.
When should I use ready-mix vs. bags?
Use bags for small projects under 1 cubic yard — things like fence posts, small pads, and repairs. For anything over 1-2 cubic yards, ready-mix truck delivery is faster, cheaper, and gives you a more consistent pour. Most companies have a minimum order of 1 cubic yard.