Concrete Calculator
Estimate the amount of concrete you need in cubic yards for slabs, sidewalks, footings, and columns. Includes cost estimation and bag counts for small projects.
Concrete is sold by the cubic yard from ready-mix trucks, or by the 60- or 80-pound bag at hardware stores. Knowing exactly how much you need before ordering is critical: short orders during a pour are very expensive (callback trips, cold joints between batches), while over-ordering wastes money on returned concrete.
This calculator converts a project's length × width × depth into cubic yards, number of 60- and 80-pound bags for small jobs, and total cost at your local ready-mix price. The basic formula is straightforward; the practical issues are choosing the right depth, accounting for waste, and deciding between bags and a truck.
The truck-vs-bag breakpoint is about 1 cubic yard. Below that, bags from a home store usually win on convenience and cost. Above 1 yard, ready-mix delivery is cheaper, faster, and far less back-breaking. Most ready-mix trucks have a minimum delivery charge (~$80–150) that erases the savings on very small loads.
Inputs
Results
Cubic Yards Needed
2.47
With 10% Extra
2.72
Estimated Cost
$407.41
Concrete Breakdown
| Measurement | Value |
|---|---|
| Area | 200 sq ft |
| Depth | 4 inches (0.33 ft) |
| Volume | 66.7 cubic feet |
| Cubic Yards (exact) | 2.47 |
| Cubic Yards (+10%) | 2.72 |
| 40 lb Bags Needed | 223 |
| 60 lb Bags Needed | 149 |
| 80 lb Bags Needed | 112 |
Formula
How to use this calculator
- Measure length and width of the slab in feet.
- Choose depth in inches. Standards: patio/sidewalk 4 inches, driveway 5–6 inches, garage floor 6 inches, heavy-equipment pad 8+ inches.
- Enter the local ready-mix price (varies $120–180 per cubic yard depending on region and order size).
- Round result up to the next ¼ yard when ordering ready-mix; trucks typically deliver in ¼-yard increments.
- Add 5–10% for spillage, edges, and uneven ground.
- For irregular shapes, compute each rectangular section separately and sum.
- For deep footings or columns, use cylindrical or rectangular prism formulas (length × width × depth for rectangular; π × radius² × depth for cylindrical).
Worked examples
Standard patio
12 × 16 patio, 4 inches deep. Volume: (12 × 16 × 4) / 324 = 2.37 cubic yards. Order: 2.5 yards from ready-mix at $150/yd = $375. For DIY bag pour: ~107 80-lb bags ≈ $750. Truck wins handily at this size.
Driveway
Driveway 30 × 12 × 5 inches = (30×12×5)/324 = 5.56 cubic yards. Order 6 cubic yards. At $145/yd + $100 delivery = $970. This is squarely in truck-delivery territory; bags would mean ~250 bags and many hours of mixing.
When to use this calculator
Use this calculator for any pour: patios, walkways, driveways, garage floors, shed pads, footings, post holes, columns, retaining walls. The math is the same; the depth and rebar requirements change.
Key references for depth: - Sidewalks/patios with foot traffic: 4 inches - Driveways: 5–6 inches with rebar grid - Garage floors: 6 inches - Equipment pads / RV pads: 8+ inches - Footings: per local building code (usually 8–12 inches deep, 16–24 inches wide for residential)
For real construction work, get a permit if required by your jurisdiction and follow local building codes for rebar, vapor barriers, and frost depth. Bad concrete work is hard and expensive to fix.
Common mistakes to avoid
- Underestimating waste. 5–10% is necessary; many jobs need 12–15% on uneven ground.
- Mixing depth units. Plug depth into the formula in inches (the formula expects it), or convert to feet first.
- Forgetting delivery and short-load fees. Below ~3 yards, ready-mix often adds $50–150 in fees.
- Skipping rebar/wire mesh on slabs >100 sq ft. Without reinforcement, slabs crack within a few freeze-thaw cycles.
- Pouring on uncompacted base. Inadequate gravel base under the slab leads to settling and cracks.
- Pouring in extreme heat or cold without precautions. Concrete cures predictably between ~50°F and ~85°F; outside that range you need additives, blankets, or hot water.
Frequently Asked Questions
Sources & further reading
- Concrete construction guide — Portland Cement Association
- Residential concrete slab guidelines — American Concrete Institute