Instantly calculate cubic yards for slabs, driveways, footings, and walls. Add your local concrete price to get an estimated material cost.
Typical residential slab: 4 in. Driveway: 4–6 in.
10% is standard; add more for irregular subgrade.
Typical wall footing: 12–24 in (1–2 ft) wide.
Depth to bottom of footing from top of concrete.
—
Cubic yards exact
—
Cubic yards with waste
—
80 lb bags (if bagging)
Pro tip: For anything over ~1 yard, ready-mix is more cost-effective than bags.
At current prices, bagging costs $80–120 more per yard versus ordering a truck.
$/CY
—
Need to estimate a complex shape?
ConCal's free drawing tool handles irregular slabs, L-shaped driveways, combined footings and slabs — anything that doesn't fit a simple formula. Draw it on the canvas, get exact cubic yards, and build a full bid in minutes.
Use these standard thicknesses as a starting point. Local codes, soil conditions, and load requirements may require adjustments.
Application
Recommended Thickness
PSI Mix
Notes
Patio / Walkway
4 inches
3,000 PSI
Broom or exposed finish
Residential Driveway
4–6 inches
4,000 PSI
6 in. if heavy trucks/RVs expected
Garage Floor
4–5 inches
3,500 PSI
Thicken edges to 6 in. at perimeter
Basement Floor
4 inches
3,000 PSI
Vapor barrier recommended below
Footing (residential)
8–12 inches deep
3,000 PSI
Width = 2× wall width minimum
Equipment Pad
6–8 inches
4,000 PSI
May require rebar per spec
Commercial Slab
6+ inches
4,000–5,000 PSI
Engineer-designed reinforcement
Bags vs. Ready-Mix Reference
80 lb bags yield approximately 0.60 cubic feet each. 60 lb bags yield about 0.45 cu ft. One cubic yard = 27 cubic feet.
Area (4 in. thick)
Cubic Yards
80 lb Bags Needed
Recommendation
5 × 5 ft
0.31 CY
14 bags
Bags OK
10 × 10 ft
1.23 CY
56 bags
Ready-mix usually cheaper
12 × 20 ft
2.96 CY
134 bags
Order ready-mix
20 × 20 ft
4.94 CY
222 bags
Order ready-mix
20 × 40 ft (driveway)
9.88 CY
445 bags
Order ready-mix
30 × 50 ft
18.52 CY
833 bags
Order ready-mix
The Concrete Volume Formula
Understanding the math behind the calculator helps you catch mistakes on the job site and quickly sanity-check supplier quotes.
CY = (Length ft × Width ft × Thickness in ÷ 12) ÷ 27
Example — 20 × 20 slab, 4 in. thick:
= (20 × 20 × 4/12) ÷ 27
= 133.33 ÷ 27
= 4.94 CY → order 5.44 CY with 10% waste
For circles: CY = π × (diameter/2)² × thickness_in ÷ 12 ÷ 27
For footings: length and width are in feet, depth is in inches — same formula applies.
Frequently Asked Questions
Common questions from contractors and homeowners about concrete quantities.
How many bags of concrete for a 10×10 slab?
▼
A 10×10 ft slab at 4 inches thick requires about 1.23 cubic yards of concrete. Using 80 lb bags (which yield roughly 0.60 cubic feet each), you'd need approximately 61 bags. For a slab this size, ordering ready-mix is usually cheaper and faster — call a local batch plant for a quote. Always add 10% extra to account for waste, spills, and uneven subgrade.
How thick should a driveway be?
▼
A residential driveway should be at least 4 inches thick for passenger vehicles. For heavier loads — trucks, RVs, or commercial vehicles — use 5 to 6 inches. In cold climates, a deeper base layer (4–6 inches of compacted gravel) is critical to prevent frost heave and cracking. ACI 330 recommends 4 inches minimum for residential driveways with a 4,000 PSI mix.
How do I calculate cubic yards of concrete?
▼
Multiply Length (ft) × Width (ft) × Thickness (in) ÷ 12, then divide by 27 to convert cubic feet to cubic yards. Example: a 20×20 slab at 4 inches: 20 × 20 × (4/12) = 133.33 cu ft ÷ 27 = 4.94 CY. Always add 10% for waste. For irregular shapes or combined jobs with footings, ConCal's drawing tool gives you a precise measurement.
How much does a cubic yard of concrete cost?
▼
Ready-mix concrete typically costs $130–$200 per cubic yard depending on your region, PSI spec, and supplier. Higher-strength mixes (4,000–5,000 PSI) cost $10–$30 more per yard. Short-load fees may apply for orders under 5 yards. Get quotes from at least two local batch plants before bidding a job.
How thick should a concrete slab be?
▼
Residential slabs (patios, garage floors, sidewalks) are typically 4 inches thick. Driveways should be 4–6 inches. Industrial floors and heavy-load areas require 6 inches or more. Thickened edges (8–12 inches deep, 12 inches wide) are recommended around the perimeter of exterior slabs to resist frost and settlement. Always consult local building codes for structural slabs.
What's the difference between cubic feet and cubic yards?
▼
There are 27 cubic feet in one cubic yard (3 ft × 3 ft × 3 ft). Concrete is sold and ordered by the cubic yard (or "yard") in the United States. Your calculator results are in cubic yards — that's the number to give your concrete supplier when ordering ready-mix.
Estimate the full job, not just the concrete
ConCal calculates concrete plus labor, forms, rebar, base prep, and equipment — then generates a client-ready PDF proposal. Free to use, no account required.