Concrete Calculator
Calculate concrete volume, bags needed, and cost for slabs, footings, and walls
Calculate Concrete
Professional-grade accuracy
Ready-mix typically $125-$150/yard
10% for DIY, 5% for pros
💡 Professional Tips
- 1Always add 5-10% waste factor to avoid running short
- 2Ready-mix concrete is more economical than bags for projects over 1 cubic yard
- 3Standard driveway thickness: 4 inches (6 inches for heavy vehicles)
- 4Ensure truck access before ordering—trucks need 10 ft width clearance
- 5Concrete begins setting in 90-120 minutes—have forms and crew ready
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How to Use This Calculator
Using the Concrete Calculator is straightforward and designed for both professionals and DIY enthusiasts. Start by selecting your project type from the dropdown menu—whether you're working on a slab, footing, wall, or column. This helps the calculator apply the correct formula for your specific needs. Next, enter the dimensions of your project in feet and inches. For slabs, you'll input length, width, and thickness. For footings and walls, enter length, width, and height. The calculator automatically converts all measurements to the proper units.
After entering your dimensions, the calculator instantly displays results in multiple formats. You'll see the total volume needed in cubic yards (the standard ordering unit for ready-mix concrete), cubic feet for smaller projects, and the number of 80-pound bags required if you're mixing your own. The calculator also accounts for waste—typically 5-10% extra to ensure you don't run short due to spillage, over-excavation, or calculation discrepancies.
For cost estimation, enter your local concrete price per cubic yard or per bag. Ready-mix concrete typically costs between $125-$150 per cubic yard depending on your location and the concrete mix specification. The calculator will show your total material cost, helping you budget accurately. You can also adjust the waste factor percentage based on your experience level and project complexity—beginners should use 10%, while experienced contractors might reduce this to 5%.
The calculator includes advanced features for complex projects. You can add multiple pours to calculate total concrete needed for an entire job. For example, if you're pouring a driveway plus a walkway, calculate each separately and the tool will sum the totals. You can also switch between different concrete strengths (2,500 PSI, 3,000 PSI, 4,000 PSI) which may affect pricing. The results update in real-time as you modify any input, making it easy to compare different scenarios and optimize your order.
Understanding Concrete Calculations
Concrete is one of the most versatile and widely used construction materials in the world, consisting of cement, sand, gravel (aggregate), and water mixed in specific proportions. Understanding concrete calculations is crucial because ordering too little means costly delays and potential cold joints (weak spots where new concrete meets cured concrete), while ordering too much wastes money—unused concrete cannot be returned and must be disposed of properly. A single cubic yard of concrete weighs approximately 4,000 pounds and costs $125-$150, so accurate calculations directly impact your project budget.
The fundamental concept in concrete calculation is volume—determining how much three-dimensional space your concrete will fill. Volume is always measured in cubic units (cubic feet or cubic yards) because concrete fills a three-dimensional form. One cubic yard equals 27 cubic feet (3 feet × 3 feet × 3 feet), and this is the standard unit concrete suppliers use for ready-mix orders. For bagged concrete, calculations convert to the number of 80-pound bags, where each bag yields approximately 0.60 cubic feet of mixed concrete.
Different project types require different calculation approaches. Slabs (driveways, patios, garage floors) are rectangular with length × width × thickness. Footings are typically rectangular trenches that support foundation walls. Walls are vertical structures calculated as length × height × thickness. Columns or piers are often circular, requiring π × radius² × height. Understanding which formula applies to your project type is essential for accurate estimates. The calculator automatically selects the correct formula based on your project selection.
Concrete strength, measured in PSI (pounds per square inch), affects both cost and application. Standard 2,500-3,000 PSI concrete works for most residential slabs and footings. Higher-strength 4,000-5,000 PSI concrete costs 10-15% more but is required for structural elements, cold climates with freeze-thaw cycles, or heavy-duty applications like commercial driveways. Your local building code specifies minimum strength requirements—always verify before ordering.
The waste factor is a critical but often overlooked component of concrete estimation. Professional contractors typically add 5-10% extra concrete to account for spillage during transport and pouring, over-excavation (when the excavated area is slightly larger than planned), ground settlement, and measurement errors. For a 10 cubic yard pour, a 10% waste factor means ordering 11 yards. This insurance policy prevents the nightmare scenario of running short mid-pour, which requires emergency orders at premium prices and creates weak cold joints in your finished concrete.
Formula & Calculations
The basic formula for concrete volume varies by shape, but the principle is always the same: calculate the volume of the space the concrete will occupy. For rectangular slabs, the formula is Volume = Length × Width × Thickness. All dimensions must be in the same units—typically feet for construction. For example, a 20-foot by 30-foot driveway with 4-inch thickness: First convert thickness to feet (4 inches = 0.333 feet), then Volume = 20 × 30 × 0.333 = 199.8 cubic feet.
To convert cubic feet to cubic yards (the standard ordering unit), divide by 27. Using our driveway example: 199.8 ÷ 27 = 7.4 cubic yards. Adding a 10% waste factor: 7.4 × 1.10 = 8.14 cubic yards, which rounds to 8.5 yards for ordering (concrete suppliers typically deliver in half-yard increments). This formula applies to any rectangular pour: sidewalks, patios, garage floors, or basement slabs.
For circular elements like columns or piers, use the formula Volume = π × r² × h, where r is the radius (half the diameter) and h is the height. For example, a round column that's 12 inches in diameter and 8 feet tall: radius = 6 inches = 0.5 feet, so Volume = 3.14159 × 0.5² × 8 = 6.28 cubic feet = 0.23 cubic yards. Multiple columns require multiplying this volume by the number of columns needed.
When calculating bagged concrete, each 80-pound bag produces approximately 0.60 cubic feet when mixed. To find bags needed, divide total cubic feet by 0.60. Using our driveway example of 199.8 cubic feet: 199.8 ÷ 0.60 = 333 bags. At $4.50 per bag, this costs $1,498.50—significantly more expensive than ready-mix at ~$1,100 for 8.5 yards. Bagged concrete makes sense only for very small projects (under 1 cubic yard) or locations where concrete trucks cannot access.
Key Factors to Consider
Thickness is the most critical factor in concrete slab calculations and directly relates to the application. Residential driveways typically require 4 inches of thickness, adequate for standard passenger vehicles. If you park RVs, boats, or frequently have heavy deliveries, increase to 5-6 inches. Commercial driveways and loading areas need 6-8 inches. Garage floors are typically 4 inches. Sidewalks can be 4 inches, but 3.5 inches is acceptable for light foot traffic. Patios are usually 4 inches. Always check local building codes—some jurisdictions mandate minimum thicknesses for specific applications.
Subgrade preparation dramatically affects how much concrete you'll need and the longevity of your project. A properly compacted gravel base (4-6 inches of crushed stone) provides drainage and prevents settling. If your excavation is uneven or the subgrade isn't compacted, you'll need additional concrete to fill low spots—potentially 10-20% more than calculated. Professional contractors use a laser level or string line to ensure consistent excavation depth. Poor subgrade preparation causes cracking, settling, and premature failure, wasting your entire concrete investment.
Reinforcement requirements affect both the concrete order and project cost. Most slabs require wire mesh (6×6 inch, 10-gauge) or rebar depending on application and local codes. Driveways often need #3 or #4 rebar in a 18-24 inch grid pattern. Structural elements like footings and walls always require rebar per engineering specifications. Fiber-reinforced concrete (with synthetic or steel fibers mixed in) costs $5-10 more per yard but can replace wire mesh in some applications. Include reinforcement costs when budgeting—rebar and wire mesh can add $0.50-$2.00 per square foot.
Concrete mix design affects both performance and cost. Standard mixes include 2,500 PSI (light duty, minimal freeze-thaw), 3,000 PSI (most residential slabs and footings), 3,500 PSI (driveways, moderate climate), 4,000 PSI (structural, cold climate, heavy duty), and 5,000+ PSI (commercial, industrial). Higher strength concrete costs incrementally more—typically $5-10 per yard for each 1,000 PSI increase. Special admixtures like air entrainment (required in freeze-thaw climates), accelerators (for cold weather), retarders (for hot weather), or fibers (for crack resistance) each add $5-15 per yard.
Delivery and placement logistics significantly impact your project. Ready-mix trucks can discharge concrete up to 12-15 feet from where they're parked via chute. Beyond this, you'll need concrete pumping ($300-800 additional depending on distance and volume) or wheelbarrows (extremely labor-intensive and only practical for small pours). Truck access is critical—ensure your site has a clear path at least 10 feet wide and overhead clearance of 14 feet. Concrete begins setting in 90-120 minutes in summer, less in hot weather, so have your forms ready, reinforcement installed, and adequate crew on hand before the truck arrives. Demurrage charges ($2-3 per minute) apply if the truck waits on-site beyond the standard discharge time.
Frequently Asked Questions
1How much does a yard of concrete cost?
Ready-mix concrete typically costs between $125-$150 per cubic yard for standard residential mixes (3,000-4,000 PSI). Prices vary by location, with urban areas generally cheaper than rural locations due to shorter delivery distances. Small loads (under 5 yards) often incur short-load fees of $50-100. Special mixes with admixtures (fiber, color, accelerators) add $5-15 per yard. High-strength concrete (5,000+ PSI) costs $10-20 more per yard. Delivery fees typically apply for distances beyond 10-15 miles from the batch plant. Always request quotes from multiple suppliers as prices can vary 15-20% in the same market.
2How many 80-lb bags of concrete equal a yard?
You need 45 bags of 80-pound concrete to equal one cubic yard. Each 80-pound bag yields approximately 0.60 cubic feet when mixed, and one cubic yard equals 27 cubic feet (27 ÷ 0.60 = 45 bags). However, bagged concrete is significantly more expensive—45 bags at $4.50 each = $202.50 versus $125-$150 for ready-mix. Bagged concrete makes economic sense only for very small projects under 0.5 yards (about 20 bags) or where concrete truck access is impossible. For projects requiring 1+ cubic yards, always use ready-mix to save money and labor.
3What is the minimum concrete delivery?
Most ready-mix suppliers have a minimum order of 1 cubic yard, though many charge short-load fees for orders under 5-10 yards. Short-load fees typically range from $50-$150 depending on the supplier and how far below their preferred minimum you order. For very small projects (under 1 yard), bagged concrete from a home improvement store is often more economical despite the higher per-yard cost. Some suppliers offer "partial load" or "short-load" services specifically for small projects. Always call ahead to understand minimum order requirements and fees in your area.
4How thick should a concrete slab be?
Standard concrete slab thickness depends on application: residential driveways and garage floors need 4 inches minimum, increasing to 5-6 inches for heavy vehicles (RVs, boats, trailers). Sidewalks and patios typically require 4 inches, though 3.5 inches works for light foot traffic patios. Basement floors are usually 4 inches over compacted gravel. Commercial driveways need 6-8 inches. Always check local building codes as some jurisdictions mandate specific thicknesses. Thicker slabs provide greater strength and longevity but increase material costs proportionally—a 6-inch slab requires 50% more concrete than a 4-inch slab.
5Do I need rebar in a concrete slab?
Rebar requirements depend on slab size, thickness, soil conditions, and local building codes. Most 4-inch residential slabs (driveways, patios, garage floors) require wire mesh (6×6, W1.4×W1.4) as minimum reinforcement. Driveways longer than 30 feet or in expansive soils often require #3 or #4 rebar in 18-24 inch grid patterns. Structural slabs, slabs thicker than 5 inches, or those bearing significant loads always need rebar per engineering specifications. Some contractors use fiber-reinforced concrete as a wire mesh alternative for light-duty slabs. Always consult local building codes and consider soil report recommendations—poor soils may require additional reinforcement regardless of slab size.
6How long does concrete take to cure?
Concrete reaches initial set (hard enough to walk on) in 24-48 hours, but full strength takes 28 days. You can drive on a new driveway after 7 days for passenger vehicles, but wait 28 days before parking heavy trucks or RVs. Remove forms from walls and footings after 24-48 hours. Keep concrete moist during curing (spray with water or use curing compound) especially in first 7 days to achieve full strength and prevent cracking. Hot weather accelerates setting but can reduce final strength if concrete dries too quickly. Cold weather (below 50°F) dramatically slows curing—use insulated blankets and heated enclosures in winter.
7Why should I add a waste factor when ordering concrete?
A waste factor (typically 5-10%) ensures you have enough concrete to complete your pour without running short. Running short mid-pour is catastrophic—emergency concrete orders cost 50-100% more, trucks may not be available, and the delay creates cold joints (weak spots where new concrete bonds to partially cured concrete). Waste accounts for spillage during transport and pouring, over-excavation (holes often larger than measured), ground settlement, measurement errors, and irregular forms. Experienced contractors use 5% waste factors; DIYers should use 10%. Leftover concrete can be used for small projects (stepping stones, fill low spots) or disposed of on-site in designated areas. The small cost of ordering extra concrete provides insurance against project failure.