Quick Answer
Concrete Calculator Concrete Calculator calculates concrete volume by multiplying length × width × thickness, then converting to cubic yards and bag counts.
Typical result: For a typical 20 ft × 10 ft patio slab at 4 inches thick, you need about 2.5 cubic yards of concrete.
Range: One cubic yard covers about 80 sq ft at 4 inches thick, or about 65 sq ft at 5 inches thick.
Depends on: thickness, area dimensions, and waste factor
How to Use This Concrete Calculator
Enter the dimensions of the area you want to cover, or switch to Total area mode if you already know the square footage. Then enter the material thickness, choose a density preset or custom density, add a waste factor, and optionally enter a price per unit to estimate material cost.
- Enter the project dimensions (length × width or total square footage).
- Choose the concrete slab thickness.
- Select a waste factor. 5% is common for rectangular slabs, 10% for irregular shapes or stairs.
- Enter price per cubic yard if you want a material cost estimate.
- Click Calculate to see concrete volume in cubic yards, cubic feet, and bag counts.
Assumptions & Methodology
This calculator uses standard volumetric estimating for concrete material planning. Results are shown in cubic yards, cubic feet, and equivalent bag counts (60-lb and 80-lb bags).
The waste factor helps account for spillage, uneven grade, form gaps, and over-excavation. A 5% waste factor is typical for simple rectangular slabs. Use a higher factor for irregular shapes, stairs, or complex layouts.
Enter the compacted or finished slab thickness. Confirm thickness with your contractor, local building code, or project specification before ordering.
| Assumption | Default Value | Notes |
|---|---|---|
| Volume unit | Cubic yards | Standard ready-mix ordering unit in the US |
| Bag equivalents | 60-lb and 80-lb | Standard premixed bag sizes at home improvement stores |
| Waste factor | 5% | Suitable for simple rectangular slabs |
| Thickness | User input | Use finished slab thickness, not excavation depth |
| Cost estimate | Optional | Material cost only, not full installed project cost |
Calculation Formula
Volume (cubic feet) = Length (ft) × Width (ft) × Thickness (ft)
Volume (cubic yards) = Volume (cubic feet) ÷ 27
Total Concrete = Volume × (1 + Waste Factor)
Estimated Cost = Total Concrete × Price Per Cubic Yard
Bag count (80-lb)
Bags = Cubic yards × 45
Bag count (60-lb)
Bags = Cubic yards × 60
Example Estimate
A 20 ft by 10 ft patio slab with 4 inches of concrete has an area of 200 sq ft and a volume of about 66.67 cubic feet, or about 2.47 cubic yards.
Using a standard volume calculation, the raw concrete needed is about 2.47 cubic yards.
With a 5% waste factor, the total concrete needed is about 2.59 cubic yards.
The total material needed is about 2.59 cubic yards.
If concrete costs $140 per cubic yard, the estimated material cost would be about $363. This is only an example price. Local concrete prices vary by supplier, region, quantity, and delivery distance. This does not include delivery, labor, formwork, or reinforcement.
Quick Reference
| Thickness | Coverage per Cubic Yard | Typical Use |
|---|---|---|
| 3 inches | ~108 sq ft | Walkways, shed slabs |
| 4 inches | ~81 sq ft | Patios, driveways, residential slabs |
| 5 inches | ~65 sq ft | Garage floors, heavier loads |
| 6 inches | ~54 sq ft | Foundation walls, heavy equipment |
| 8 inches | ~40 sq ft | Commercial slabs, loading docks |
| Project Type | Typical Thickness | Best For | Notes |
|---|---|---|---|
| Residential patio | 4 inches | Foot traffic, light furniture | Add reinforcement mesh for crack control |
| Driveway | 4–5 inches | Passenger vehicles | Use 5 inches for heavier vehicles or RVs |
| Garage slab | 5–6 inches | Cars, light trucks | May need rebar depending on load |
| Foundation footing | 8–12 inches | Load-bearing walls | Confirm with structural engineer |
| Sidewalk / walkway | 4 inches | Pedestrian use | Add control joints every 4–5 feet |
| Bag Size | Bags per Cubic Yard | Coverage per Bag (4 in) |
|---|---|---|
| 60-lb bag | ~60 | ~1.35 sq ft |
| 80-lb bag | ~45 | ~1.8 sq ft |
What Affects Cost?
Concrete material cost is usually estimated by multiplying the required cubic yards by the price per cubic yard. However, the final project cost includes several additional factors beyond just material cost.
Material Cost = Cubic Yards × Price Per Cubic Yard
The total installed cost typically includes:
- Material cost: Cubic yards × price per cubic yard
- Delivery: Ready-mix truck dispatch and travel time
- Labor: Pouring, screeding, and finishing crew
- Formwork: Boards, stakes, and release agent
- Reinforcement: Rebar, wire mesh, or fiber additive
- Finishing: Broom, trowel, or stamped finish
- Curing: Curing compound or moisture retention
- Excavation / sub-base: Gravel base and compaction
- Permits and inspections: Local building permits and code compliance
Bagged Concrete vs Ready-Mix
Choosing between bagged concrete and ready-mix delivery depends on project size, access, and timeline. Use this guide to decide which is more practical for your job.
Use ready-mix for large pours
Projects over 2 cubic yards are usually more economical with ready-mix delivery. Bag mixing becomes labor-intensive and inconsistent beyond this threshold.
Use bagged concrete for small repairs
For patches under 1 cubic yard, 60-lb or 80-lb bags from a home improvement store are practical and do not require a truck delivery minimum.
Consider access and placement
Ready-mix trucks need driveway or pump access. If access is limited, bagged concrete or a concrete pump may be required.
Concrete Order Checklist
Before calling a ready-mix supplier or buying bags, confirm these details to avoid over-ordering or under-ordering.
Total project area
measured in square feet
Slab thickness
use finished thickness, not excavation depth
Waste factor
typically 5% for rectangles, 10% for stairs or irregular shapes
Bag size preference
60-lb or 80-lb if mixing by hand
Delivery access
truck access or need for concrete pump
Reinforcement plan
rebar, mesh, or fiber — ordered separately
Finish type
broom, smooth trowel, or stamped
Weather and cure time
avoid rain and extreme heat during pour
Concrete Calculator FAQ
How do I calculate how much concrete I need?
Multiply the length × width × thickness of your project to get the volume in cubic feet, then divide by 27 to get cubic yards. This calculator handles all unit conversions — just enter your dimensions, thickness, and it converts to cubic yards and bags automatically.
Should I order concrete by cubic yards or bags?
Large projects (driveways, slabs, foundations) are typically ordered by the cubic yard from a ready-mix supplier. Small projects (sidewalk patches, small patios) can use 60-lb or 80-lb premixed bags. One cubic yard is equivalent to about 45 × 80-lb bags or 60 × 60-lb bags.
What thickness should I use for a concrete slab?
Typical residential slabs are 4 inches thick. Driveways often need 4–5 inches. Patios and walkways are usually 4 inches. Garage floors and heavy-duty areas may need 5–6 inches. Foundations and footings depend on local building codes and engineer specifications.
How much waste factor should I use?
A 5% waste factor is typical for simple rectangular slabs. For irregular shapes, stairs, footings, or when using bagged concrete, use 8–10%. The waste factor accounts for spillage, uneven grade, form gaps, and over-excavation.
Why is my contractor's estimate higher than the calculator?
This calculator estimates material quantity only. A contractor's quote includes material cost plus delivery (ready-mix truck), labor, formwork, reinforcement (rebar or mesh), finishing, curing, and overhead. Always get a detailed written quote before ordering.
Can I use this calculator for foundations?
Yes, enter the foundation length, width, and wall thickness. For spread footings, enter the footing dimensions. Confirm structural requirements with your contractor or engineer before ordering.
How many bags of concrete make a cubic yard?
About 45 bags of 80-lb concrete mix make one cubic yard. About 60 bags of 60-lb mix make one cubic yard. This calculator converts cubic yards to both 60-lb and 80-lb bag counts automatically.
Does this calculator include labor or delivery cost?
No. The estimated cost is material cost only, based on cubic yards multiplied by price per cubic yard. It does not include delivery, labor, formwork, reinforcement, finishing, or contractor overhead. Contact a local ready-mix supplier or contractor for a full project quote.
How accurate is this concrete calculator?
This calculator provides a reasonable planning estimate based on standard volume calculations. Actual material needs may vary due to sub-base conditions, form gaps, over-excavation, and consolidation. Always confirm quantities with your contractor or supplier before ordering.
Calculation Methodology
This calculator uses standard volumetric estimating for planning purposes. Default waste values are common planning assumptions and may not match every concrete mix, site condition, or local specification. Confirm final quantities with a contractor or ready-mix supplier before ordering.
Reviewed by: Construction Tools Station Editorial Team
Last updated: May 2026