How Much Concrete Do I Need?
Calculate the exact amount of concrete for slabs, footings, walls, and columns. Get results in cubic yards and number of bags with cost estimates.
Quick Answer
A 10×12 ft patio slab at 4 inches thick needs about 1.48 cubic yards of concrete (~67 bags of 80-lb mix), with ready-mix material alone roughly $178–$252 (1.48 yd³ × $120–$170).
Enter your dimensions above to calculate concrete needed.
💡 1 cubic yard of concrete covers approximately 81 sq ft at 4 inches thick
How to Calculate Concrete Needed
Formula
Length (ft) × Width (ft) × Thickness (in) ÷ 324 = Cubic Yards
Multiply your slab's length by width to get square footage. Multiply by thickness in inches, then divide by 324 to convert to cubic yards.
Example
For a 10 ft × 12 ft patio slab at 4 inches thick: 10 × 12 × 4 ÷ 324 = 1.48 cubic yards. That's about 67 bags of 80-lb concrete mix.
Tips & Best Practices
- •Order 5–10% extra concrete to account for spillage, uneven ground, and forms.
- •Four inches is a common residential flatwork starting point, not a universal design requirement — thickness depends on use, loading, soil support and project design.
- •One 80-lb bag of concrete mix yields about 0.6 cubic feet. You need 45 bags per cubic yard.
- •For projects over 1 cubic yard, consider ordering ready-mix delivery instead of mixing bags.
Quick Reference
1 cubic yard of concrete covers approximately 81 sq ft at 4 inches thick
How Many Bags of Concrete Do I Need?
You need approximately 45 bags of 80-lb concrete mix per cubic yard, or about 60 bags of 60-lb mix per cubic yard.
The table below shows how many bags you need for common slab sizes at 4 inches thick — a common residential planning thickness for patios and walkways.
Planning slab thickness: Four inches is a common residential flatwork starting point, not a universal design requirement.
| Slab Size | Cubic Yards | 80-lb Bags | Ready-Mix Material |
|---|---|---|---|
| 4×4 ft | 0.20 yd³ | ~9 bags | $24–$34 |
| 8×10 ft | 0.99 yd³ | ~45 bags | $119–$168 |
| 10×12 ft | 1.48 yd³ | ~67 bags | $178–$252 |
| 12×20 ft | 2.96 yd³ | ~133 bags | $355–$503 |
| 20×24 ft (2-car garage) | 5.93 yd³ | ~267 bags | $712–$1,008 |
For projects over 1 cubic yard, ready-mix delivery is usually cheaper and faster than mixing bags by hand.
How Thick Should a Concrete Slab Be?
Concrete thickness depends on the use, loading, soil support and project design. Four-inch and five-inch slabs are common residential flatwork examples, but they are not universal requirements.
The American Cement Association describes 4- and 5-inch slabs as common examples for driveways and walks, not as design requirements. Local requirements and site conditions control.
Patios & Walkways — around 4 inches
Around 4 inches is a common planning thickness for residential patios and walks, but local requirements and site conditions control.
Driveways — planning starting point
A 4-inch slab is a common residential planning starting point for passenger-vehicle use on well-prepared support. Heavier vehicles, weak soils or project-specific requirements can justify additional thickness or structural design.
Garage Floors & Heavier Loads
Heavy loads and equipment can call for a thicker slab or a structural design. Thickness and reinforcement should follow the project design or local requirements.
Shed Pads — often around 4 inches
A 4-inch slab is a common planning thickness for lightly loaded storage sheds; check the shed manufacturer's and local requirements. Extending the slab a few inches beyond the shed footprint is a common practical allowance.
Base, Joints, Reinforcement & Curing
Base and subgrade. Concrete needs stable, uniform support. Base requirements depend on soil conditions, drainage, slab use and local/project requirements. A compacted granular base is commonly used where improved support, drainage or grade correction is needed, but it is not one universal thickness for every slab. Gravel alone does not prevent cracking.
Joints. Contraction joints help control where shrinkage cracks form; they do not guarantee a crack-free slab. For conventional slabs, joint depth should be at least about one-quarter of the slab thickness. Joint layout depends on slab thickness and geometry — panels should be kept approximately square where practical, and long narrow panels are more prone to random cracking. See the American Cement Association guide for jointing and finishing guidance.
Reinforcement. Reinforcement does not prevent concrete from cracking. Properly designed and positioned reinforcement can help control crack width and maintain load transfer after cracking. Bar size and spacing depend on the project design, not one rule for every driveway.
Strength and durability. Required concrete strength depends on local requirements, exposure conditions and project design. Exterior concrete exposed to freezing, moisture and deicing salts may require durability provisions beyond compressive strength alone, including appropriate air entrainment and mixture requirements.
Curing and traffic. Curing means maintaining suitable moisture and temperature so the concrete can continue developing its intended properties — it is not simply waiting for it to dry (see ACI's curing FAQ). A seven-day curing period is commonly adequate for normal concrete under conventional conditions, but mix design, weather and project requirements can change the method or duration. When a slab can accept foot or vehicle traffic depends on strength development, curing conditions, weather and loading; follow your concrete supplier or contractor's guidance for the actual mix and conditions.
How Much Does Concrete Cost?
Ready-mix concrete is about $120–$170 per cubic yard as a broad residential planning range. Supplier, mix, delivery distance, short-load fees and additives can move the actual price outside this range, and specialty, high-strength or decorative concrete may not fit it. Bagged concrete mix costs $3–$5 per 80-lb bag, or roughly $135–$225 per cubic yard mixed yourself.
A basic poured residential slab is about $4–$8 per square foot installed, and a plain, basic-finish driveway about $6–$8 per square foot installed. Site preparation, difficult access, thicker slabs, reinforcement, decorative finishes and demolition/removal can increase the total. The table below keeps two categories separate: ready-mix material alone (at a 4-inch planning thickness) and the installed price — do not add them together.
| Project | Size | Ready-Mix Material | Installed (basic) |
|---|---|---|---|
| Small patio | 8×10 ft | $119–$168 | $320–$640 |
| Large patio | 12×16 ft | $284–$404 | $768–$1,536 |
| Driveway (plain) | 12×40 ft | $712–$1,008 | $2,880–$3,840 (at $6–$8/sq ft) |
| Garage floor | 20×24 ft | $712–$1,008 | $1,920–$3,840 |
Full pricing breakdown: Concrete Slab Cost: What to Expect →
Before You Order
- ☐Measure twice — running short on concrete mid-pour is a serious problem that wastes the whole batch
- ☐Decide on reinforcement with your project design or contractor — it can help control crack width but does not prevent cracking
- ☐For pours under 1 cubic yard, bags work fine; above that, ready-mix is almost always cheaper
- ☐Have crew and tools staged before the truck arrives — concrete waits for no one
- ☐Order 10% extra — unused concrete can be poured into footings or low spots nearby
Frequently Asked Questions
How much does a cubic yard of concrete cost?+
Ready-mix concrete is about $120–$170 per cubic yard as a broad residential planning range; supplier, mix, delivery distance, short-load fees and additives can move the actual price outside this range, and specialty, high-strength or decorative concrete may not fit it. Bagged concrete (mixing yourself) runs about $5–$8 per 80-lb bag, or roughly $225–$360 per cubic yard. A basic installed slab is about $4–$8 per square foot.
How many bags of concrete do I need?+
You need approximately 45 bags of 80-lb concrete mix per cubic yard, or about 60 bags of 60-lb mix per cubic yard.
How thick should a concrete slab be?+
Concrete thickness depends on the use, loading, soil support and project design. Four-inch and five-inch slabs are common residential flatwork examples, but they are not universal requirements. A 4-inch slab is a common residential planning starting point for passenger-vehicle use on well-prepared support; heavier vehicles, weak soils or project-specific requirements can justify additional thickness or structural design. Local requirements and site conditions control.
How long does concrete take to cure?+
Curing means maintaining suitable moisture and temperature so the concrete can continue developing its intended properties — it is not simply waiting for it to dry. A seven-day curing period is commonly adequate for normal concrete under conventional conditions, but mix design, weather and project requirements can change the method or duration. 28-day compressive strength is a common testing reference age, and concrete can continue gaining strength beyond that. When a slab can accept foot or vehicle traffic depends on strength development, curing conditions, weather and loading, so follow your concrete supplier or contractor's guidance.
Common Concrete Projects
Related Calculators
Need a gravel base layer?
Gravel Calculator
Landscaping around your project?
Mulch Calculator
Need sand for leveling?
Sand Calculator
Need to calculate materials for your project? Jump back to the calculator ↑