Concrete Calculator

About Concrete Calculator

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)	$140-195 (delivered, 2026 US average)
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

What PSI Concrete Should I Use?

Residential slabs and driveways typically call for 3,000-4,000 PSI concrete, with higher strengths reserved for structural and commercial work. PSI (pounds per square inch) measures compressive strength after 28 days of curing, per ASTM C39 test methods.

PSI Rating	Typical Use	Notes
2,500 PSI	Non-structural pads, small repairs	Rarely used today; most ready-mix plants start at 3,000
3,000 PSI	Sidewalks, patios, interior slabs	Standard residential mix; meets most ACI 318 minimums
3,500 PSI	Driveways, garage floors	Handles vehicle loads and freeze-thaw better than 3,000
4,000 PSI	Heavy driveways, foundations, footings	Required by most building codes for structural footings
5,000 PSI	Commercial floors, high-load areas	Used where abrasion or heavy equipment is expected
6,000+ PSI	Structural columns, bridges	Designed mixes with admixtures; engineer-specified

In cold climates (ASTM C94 Table 4), air-entrained concrete is required for outdoor slabs exposed to freeze-thaw cycles. Air content of 5-7% significantly reduces cracking during winter.

How Long Does Concrete Take to Cure?

Concrete reaches about 70% of its final strength in 7 days and the full design strength at 28 days, per ACI 308R curing guidelines. Foot traffic can start at 24-48 hours, but vehicles should wait at least 7 days on a standard 4,000 PSI driveway.

Time After Pour	Approx Strength Gained	What Is Safe
24 hours	~15%	Remove forms on vertical surfaces; light foot traffic
3 days	~40%	Foot traffic; light equipment
7 days	~70%	Light vehicles; remove most forms
14 days	~85%	Normal vehicle traffic
28 days	100%	Design strength reached; full loading

Keep the surface damp for at least the first 7 days (misting, wet burlap, or curing compound). Concrete that dries too quickly loses 30-50% of its strength and is prone to plastic shrinkage cracks. The Portland Cement Association recommends 7 days minimum for most residential work, 14 days for high-strength or structural pours.

Common Mistakes That Ruin a Concrete Pour

Mistake	What Goes Wrong	How to Avoid It
Adding water on site	Weakens the mix; 1 extra gallon per yard can drop strength by ~200 PSI	Order the correct slump (3-5 inches for slabs); do not water it down
Pouring on frozen ground	Base settles unevenly; bottom of slab never cures	Wait for ground temp above 40°F or use insulated blankets
Skipping the vapour barrier	Moisture rises through slab, damaging flooring above	10-mil polyethylene under any indoor slab (per IRC R506.2.3)
Under-compacted sub-base	Slab cracks and settles within 1-2 years	4-6 inches of compacted gravel or crushed stone under every slab
No control joints	Random cracks appear within 30 days	Saw cut joints at depth of ¼ slab thickness, within 24 hours
Finishing too early	Traps bleed water, causes surface scaling	Wait until the sheen is gone and footprint is ~¼ inch deep

Worked Example: 12 x 14 Patio Slab

A typical backyard patio, 12 feet by 14 feet, poured 4 inches thick. The volume is 12 x 14 x (4/12) = 56 cubic feet, which converts to 2.07 cubic yards. Adding a 10% waste buffer gives 2.28 cubic yards to order. At the 2026 US national average of around $165 per cubic yard for standard 3,000 PSI ready-mix, that is roughly $376 for the concrete alone, before short-load fees or delivery surcharges beyond a 15-mile radius. If you did this in 80 lb bags instead, 56 cu ft divided by 0.60 cu ft per bag equals 94 bags, which at $5-7 per bag runs $470-660 plus mixing time. Ready-mix is the clear winner at this size.

For a footing poured at the same time, say 14 feet long by 1.5 feet wide by 1 foot deep, add 21 cubic feet (0.78 cu yd). Combined with the slab, the order becomes 2.85 cubic yards, still under the typical 3-yard short-load threshold, so expect a $60-100 small-load fee on top of the per-yard price. Rounding the order up to 3 yards is usually cheaper than paying the short-load fee and helps cover the 10% waste allowance at the same time.

Concrete vs Other Common Slab Materials

Material	Typical Cost per sq ft (2026)	Lifespan	Best For
Concrete slab (4 in)	$6-12	50-80 years	Driveways, patios, foundations
Asphalt	$4-8	15-30 years	Driveways in cold climates
Pavers (concrete/brick)	$10-25	25-50 years	Patios, walkways (easy repair)
Gravel	$1-3	5-10 years (needs top-up)	Rural driveways, drainage
Stamped concrete	$12-28	25-50 years	Decorative patios, pool decks

Standard concrete has the best cost-per-year of any hard surface when you factor in lifespan, which is why it remains the default for US residential driveways and foundations.

Metric to Imperial Quick Reference

Switching between systems is common on international projects. The calculator handles this automatically but these conversions are useful to know when reading specs or ordering from suppliers.

Imperial	Metric Equivalent
1 cubic yard	0.7646 cubic metres (~765 litres)
1 cubic foot	0.0283 cubic metres (~28.3 litres)
1 inch	2.54 centimetres
1 foot	0.3048 metres
80 lb bag (0.60 cu ft)	~36 kg bag (~17 litres)
60 lb bag (0.45 cu ft)	~27 kg bag (~12.7 litres)
20 kg bag	~9 litres (~0.32 cu ft)
25 kg bag	~11 litres (~0.39 cu ft)
Concrete density	~2,400 kg/m³ (~150 lb/cu ft, ~4,050 lb/cu yd)

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. For tile work over cured concrete, use the tile calculator. All calculations run in your browser with no data stored.

Sources

• QUIKRETE - Concrete Mix product specifications (0.60 cu ft yield per 80 lb bag)
• American Concrete Institute - Publications and Standards
• ASTM C94 - Standard Specification for Ready-Mixed Concrete
• Portland Cement Association
• HomeGuide - 2026 US ready-mix concrete price data
• International Residential Code (IRC) - Chapter 5 Floor and slab requirements