Concrete Calculator
Estimate concrete volume, cubic yards, cubic feet, and pre-mixed bags for slabs, patios, post holes, footings, and stairs. Add a waste factor to avoid running short on your pour.
What-if Simulator
Simulate waste margins and thickness variations to ensure you order enough material.
The simulator models how variations in specification or site efficiency would impact the final volume and cost. Industry standard is 5-10% waste margin.
Base Target
1.36 yd³
Simulated Order
1.36 yd³
Projected Variance
Difference in required cubic yards.
How to Use the Concrete Calculator
Calculate an approximate concrete order based on project dimensions, bag yield, and waste factor. Our tool helps you estimate ready-mix orders or pre-mixed bag quantities using your project dimensions and waste factor.
Choose your project shape (slab, footing, stairs, etc.).
Enter your project dimensions.
Input your local prices for ready-mix and bags.
Review your estimated volume and required bag counts.
Use the What-If Simulator to add waste factors and avoid shortages.
Concrete Waste Factor
Real-world ground conditions are rarely perfect. We strongly suggest accounting for a safety buffer to compensate for uneven subgrades, flexible formwork, or spillage.
- 5% Waste: Standard for simple, square forms on level ground.
- 10% Waste: Recommended for most residential projects and uneven bases.
- 15% Waste: Essential for post holes, complex curves, and rough excavation.
Concrete Calculator Formulas
Our concrete volume calculator processes 3D spatial data into precise cubic yard measurements.
Cubic Yards Conversion
Yards³ = Feet³ / 27Slab, Footing, & Wall Formula
Volume = Length × Width/Height × ThicknessRound Column Formula
Volume = Pi × Radius² × Depth
Post Hole Formula
Concrete Volume = Hole Volume - Post Volume
Solid Stairs Formula
Volume = (Width × Tread Depth × Riser Height × n(n+1)) / 2
Ready-Mix Concrete vs Concrete Bags
Reliable concrete estimators help determine whether your project scale warrants a ready-mix truck delivery or manual bag placement on-site.
Cost Logic
"A single yard of concrete takes roughly 45 80-lb bags. At around 60 bags or more, it is worth comparing bagged concrete against ready-mix delivery."
Concrete Bag Yield Chart
Compare approximate concrete yields for common pre-mixed bag sizes.
| Bag Size | Approx. Yield (Cu Ft) | Bags Per Cubic Yard |
|---|---|---|
| 40 lb | 0.30 cu ft | 90 bags |
| 50 lb | 0.375 cu ft | 72 bags |
| 60 lb | 0.45 cu ft | 60 bags |
| 80 lb | 0.60 cu ft | 45 bags |
Concrete Calculation Use Cases
Concrete Slab Calculator
Use the slab calculator to estimate concrete for patios, shed bases, garage floors, and flat pads based on length, width, and thickness.
Concrete Driveway Calculator
Estimate cubic yards for residential driveways and commercial approaches based on length, width, and robust slab thickness.
Post Hole Concrete Calculator
Calculate concrete around fence posts by accurately subtracting the internal wooden/metal post displacement from the total hole volume.
Concrete Calculator FAQ
Expert guidance on calculating cubic yards and bag requirements for construction projects.
How do I calculate how much concrete I need?
Measure the length, width, and thickness of your area in feet. Multiply them together to find cubic feet, then divide by 27 to find cubic yards. (Volume = L × W × T / 27).
How many bags of concrete are in a cubic yard?
It takes about 45 80-lb bags, 60 60-lb bags, or 90 40-lb bags to make approximately one cubic yard, depending on the product yield.
How many yards of concrete do I need for a 10×10 slab?
Before waste, a 10×10 foot slab at 4 inches thick needs about 1.23 cubic yards. With the calculator's default 10% waste factor, you should order about 1.36 cubic yards.
How much concrete do I need for fence posts?
For a standard 12-inch diameter hole that is 4 feet deep with a 4-inch post, before waste this is about 0.10 cubic yards, or 5 bags of 80-lb concrete. With the calculator’s default 10% waste factor, plan for about 6 bags.
Should I order extra concrete?
Yes. It's an industry standard to recommend ordering 5–10% extra for most pours to account for uneven excavation, formwork spreading, and spillage.
Is ready-mix cheaper than bags?
Bags are practical and cost-effective for small projects under 1.5 yards. For larger pours, ready-mix is often cheaper per cubic yard and significantly reduces labor, but short-load fees and delivery charges can affect the final price.