Build a Solid Foundation: The Ultimate Concrete Estimator
Whether you are pouring a patio, setting fence posts, or building a foundation for a shed, concrete is expensive and heavy. Order too little, and you have a construction disaster (cold joints). Order too much, and you are wasting money and disposal fees. Our Advanced Concrete Calculator takes the guesswork out of the mix. It instantly converts your dimensions into Cubic Yards (for ordering a truck) and Pre-Mix Bags (for DIY projects), automatically accounting for safety margins.
How to Calculate Concrete Volume
Concrete is sold by volume, not just weight. The standard formulas used by our tool are:
- Rectangular Slabs (Patios/Driveways): Length × Width × Thickness.
Example: A 10x10 patio that is 4 inches deep. - Circular Slabs (Gazebos): π × Radius² × Depth.
- Column Footings (Sonotubes): π × Radius² × Height.
Bags vs. Ready-Mix Truck: Which Do You Need?
Once you calculate your total volume, you have a decision to make:
- Use Pre-Mix Bags (DIY): Best for projects under 1 cubic yard (approx 45 bags of 80lbs). Great for fence posts and small pads.
- Order a Truck (Ready-Mix): Best for projects over 1 cubic yard. It guarantees a consistent mix and saves your back from mixing dozens of bags by hand.
The Critical 10% Wastage Rule
Professional contractors never order the exact amount. Uneven subgrades (the dirt under your slab) and spillage can leave you short. This calculator allows you to add a Wastage Margin (typically 5-10%). It is always cheaper to buy 3 extra bags now than to drive back to the store mid-pour while your wet concrete starts to harden.
Standard Bag Yields
If you are doing mental math, here is how much concrete standard bags yield:
- 80lb Bag: Approx 0.60 cubic feet. (You need ~45 bags for 1 cubic yard).
- 60lb Bag: Approx 0.45 cubic feet. (You need ~60 bags for 1 cubic yard).
- 40lb Bag: Approx 0.30 cubic feet. (You need ~90 bags for 1 cubic yard).
Frequently Asked Questions
How thick should my concrete slab be?
4 Inches is standard for walkways, patios, and shed floors. 5-6 Inches is recommended for driveways that will hold heavy vehicles or RVs. 6+ Inches is for heavy industrial loads.
How long does concrete take to cure?
Concrete hardens in 24-48 hours (safe to walk on), but it takes 28 days to reach its full structural strength. Keep the slab wet (hydration) for the first 7 days to prevent cracking.
What is the weight of concrete?
Standard cured concrete weighs approximately 145 to 150 lbs per cubic foot (approx 4,000 lbs per cubic yard). This is why ensuring your formwork is strong is crucial—it has to hold massive weight!