Concrete Calculator

About Concrete Calculator

This concrete calculator estimates how much concrete you need for slabs, columns, or footings. Enter dimensions and get results in cubic yards, cubic feet, cubic metres, and bag counts for 60 lb and 80 lb premixed bags. Add multiple sections of different types to get a combined project total.

How Concrete Volume Is Calculated

Section Type	Formula	Example
Slab / patio	Length x Width x Depth	10 ft x 12 ft x 4 in = 40 cu ft = 1.48 cu yd
Footing	Length x Width x Depth	30 ft x 1.5 ft x 1 ft = 45 cu ft = 1.67 cu yd
Column (cylinder)	pi x r² x Height	12 in dia x 4 ft tall = 3.14 cu ft = 0.12 cu yd

All dimensions are converted to feet before calculation. Depth in inches is divided by 12, diameter in inches is divided by 12 to get the radius in feet.

Standard Concrete Thickness

Application	Minimum Thickness	Recommended	Notes
Sidewalk (pedestrian)	3.5 inches	4 inches	IRC and ACI standard for residential
Patio	3.5 inches	4 inches	Same as sidewalk; thicker if placing heavy furniture
Driveway (cars)	4 inches	5-6 inches	6 inches recommended for trucks or heavy vehicles
Garage floor	4 inches	5-6 inches	Thicker at vehicle entry point
Foundation slab	4 inches	4-6 inches	Reinforced with rebar or wire mesh
Footing	8 inches deep, 12 in wide	12-24 in deep	Depth depends on frost line and load requirements
Steps	4 inches	4-6 inches	Reinforced; use the stair calculator for dimensions
Retaining wall footing	6 inches	8-12 inches	Width typically 2x the wall thickness

Premixed Bag Yields

Bag Size	Yield per Bag	Bags per Cubic Yard	Best For
40 lb bag	~0.30 cu ft	~90 bags	Very small repairs, post holes
50 lb bag	~0.375 cu ft	~72 bags	Small patches, fence posts
60 lb bag	~0.45 cu ft	~60 bags	Small to medium DIY projects
80 lb bag	~0.60 cu ft	~45 bags	Larger DIY projects, best value per bag

For projects over 1 cubic yard (~45 bags of 80 lb), ordering ready-mix delivery is usually more practical and cheaper. A standard ready-mix truck carries 8-10 cubic yards.

Bags vs Ready-Mix Comparison

Factor	Bagged Premix	Ready-Mix Truck Delivery
Cost per cubic yard	$150-250 (bags from hardware store)	$120-180 (delivered)
Best for	Under 1 cubic yard	1+ cubic yards
Mixing	Manual (wheelbarrow or mixer)	Arrives mixed, ready to pour
Timing flexibility	Mix at your own pace	Must pour quickly once truck arrives
Delivery	Pick up at store or have delivered	Truck comes to your site
Labour	Mixing is physically demanding	Truck pours directly; less manual work
Short load fee	N/A	$50-100+ if ordering less than 3-5 yards

Concrete Coverage Examples

Project	Dimensions	Cubic Yards	80 lb Bags
Small patio	8 x 10 ft, 4 in thick	0.99	~45
Sidewalk	3 x 30 ft, 4 in thick	1.11	~50
Single-car driveway	10 x 20 ft, 5 in thick	3.09	~139 (use ready-mix)
4 fence post holes	10 in dia x 36 in deep each	0.18	~8
Garage floor	20 x 22 ft, 5 in thick	6.79	Ready-mix recommended

Tips for Ordering Concrete

Tip	Why It Matters
Order 5-10% extra	Ground is never perfectly level; forms can bulge; spillage happens
Check the weather forecast	Concrete should not be poured below 40°F or in heavy rain
Have forms ready before delivery	Ready-mix trucks charge waiting fees (typically $1-2 per minute after 5-7 minutes)
Plan for reinforcement	Rebar or wire mesh is required for driveways, structural slabs, and anything bearing load
Use 4,000 PSI mix for driveways	Standard 3,000 PSI is fine for sidewalks; driveways need higher strength for vehicle weight

For general volume calculations with other materials (gravel, mulch, fill), the cubic yards calculator handles any material type. To measure the area of your slab or pad, the square footage calculator covers various shapes. All calculations run in your browser with no data stored.