Ordering the right amount of concrete is one of the most important steps in any pour. Too little means an emergency mid-pour order (and a visible cold joint). Too much means paying for material you dump. Concrete is sold by the cubic yard, and calculating the exact volume you need requires nothing more than basic geometry and a tape measure.
Every concrete calculation starts the same way: multiply length × width × thickness to get cubic feet, then divide by 27 to convert to cubic yards.
Cubic Yards = (Length × Width × Thickness in feet) ÷ 27
Use the Concrete Slab Calculator to compute this instantly for any dimensions.
Critical rule: Always order 5–10% more concrete than your calculation shows. Subgrade irregularities, form deflection, spillage, and slight thickness variations mean you will always use more than the theoretical minimum. Running short during a pour is far more expensive than having a little left over.
Standard patio thickness is 4 inches (0.333 feet). Driveways handling passenger vehicles should be at least 4 inches; driveways for heavy vehicles (RVs, trucks) need 5–6 inches.
| Project | Dimensions | Thickness | Cubic Yards | Est. Cost |
|---|---|---|---|---|
| Small patio | 10 × 10 ft | 4 in | 1.23 yd³ | $185–$210 |
| Medium patio | 12 × 20 ft | 4 in | 2.96 yd³ | $445–$505 |
| Single driveway | 10 × 40 ft | 4 in | 4.94 yd³ | $740–$840 |
| Double driveway | 20 × 40 ft | 5 in | 12.35 yd³ | $1,850–$2,100 |
| Garage floor | 24 × 24 ft | 4 in | 7.11 yd³ | $1,065–$1,210 |
Cost estimates at $150–$170 per cubic yard for ready-mix delivery. Actual costs vary by region, distance from plant, and order size. Does not include labor, forms, rebar, or finishing.
Continuous footings (for foundation walls) are calculated as a rectangular volume: length × width × depth. A standard residential footing is 16–24 inches wide and 8–12 inches deep, running the perimeter of the structure. For a 40 × 30 foot house with 20-inch wide, 10-inch deep footings: perimeter = 140 feet, volume = 140 × (20/12) × (10/12) = 194.4 cubic feet = 7.2 cubic yards.
Cylindrical forms (like sonotubes for deck posts) use the cylinder formula: V = π × r² × h. A 12-inch diameter sonotube (r = 0.5 ft) set 42 inches deep (3.5 ft) requires: π × 0.25 × 3.5 = 2.75 cubic feet = 0.10 cubic yards per post. Ten posts need about 1.0 cubic yard. For small quantities like this, 80-pound bags of pre-mix are often more practical than ordering a truck.
Standard sidewalk dimensions are 3–4 feet wide and 4 inches thick. A 50-foot walkway at 3.5 feet wide and 4 inches thick: 50 × 3.5 × 0.333 = 58.3 cubic feet = 2.16 cubic yards.
| Option | Volume per Unit | Best For | Cost per Cubic Yard |
|---|---|---|---|
| 60-lb bag | 0.45 cubic feet | Small repairs, single posts | ~$340 |
| 80-lb bag | 0.60 cubic feet | Post holes, small pads | ~$280 |
| Ready-mix truck | Minimum 1–3 yd³ | Any pour over 1 cubic yard | $150–$170 |
Bags are more expensive per cubic yard but eliminate minimum order requirements. Most ready-mix plants charge a short-load fee for orders under their minimum (usually 3–5 cubic yards).
The crossover point is roughly 1 cubic yard. Below that, bags are more practical (no minimum order, no truck scheduling, you can work at your own pace). Above 1 cubic yard, ready-mix is dramatically cheaper and faster.
Unreinforced concrete cracks. For flatwork (patios, driveways, sidewalks), you have three common reinforcement options:
Wire mesh (6×6 W1.4/W1.4): The most common choice for residential slabs. Placed in the middle third of the slab thickness. Helps hold cracks together after they form but does not prevent cracking.
Rebar (#3 or #4 bars on 18–24 inch centers): Stronger than mesh. Required for driveways bearing heavy loads, structural slabs, and footings. Must be supported on chairs to maintain proper positioning within the concrete.
Fiber reinforcement: Synthetic or steel fibers mixed directly into the concrete. Reduces plastic shrinkage cracking and eliminates the labor of placing mesh or rebar. Not a substitute for structural reinforcement in footings.
| PSI Rating | Common Uses |
|---|---|
| 2,500 PSI | Residential footings, light-duty flatwork |
| 3,000 PSI | Sidewalks, patios, standard residential (most common) |
| 3,500 PSI | Driveways, garage floors |
| 4,000 PSI | Commercial floors, heavy traffic areas |
| 4,500+ PSI | Structural applications, industrial floors |
Most residential projects use 3,000–3,500 PSI concrete. Higher PSI costs more per yard but provides better durability and crack resistance. In freeze-thaw climates, specify air-entrained concrete regardless of PSI rating to prevent surface spalling.
Concrete steps involve calculating multiple rectangular blocks. Each step is typically 7–8 inches high (rise) and 10–12 inches deep (run) with the full width of the stairway. For a set of 4 steps that are 4 feet wide with 7.5-inch rise and 11-inch run: calculate each step as a separate block and add them together, or use the stepped-trapezoid approach. The Cubic Yards Calculator simplifies the arithmetic.
Measuring in inches but calculating in feet. A 4-inch thick slab is 0.333 feet, not 4 feet. This error produces a result 12 times too large and leads to ordering far too much concrete.
Not accounting for subgrade preparation. If your forms sit on uneven ground and the subgrade varies by 2 inches, your actual thickness ranges from 4 to 6 inches. The extra volume can add 20–30% to your theoretical calculation.
Ordering exactly the calculated amount. Theoretical calculations assume perfect conditions. Real pours always use more. The 5–10% overage rule exists because decades of experience show that waste, spillage, and subgrade irregularities always consume more material than the math predicts.
Use the Cubic Feet Calculator for volume calculations in any unit.
Calculate concrete quantities instantly. Use the free Concrete Slab Calculator for patios and driveways, the Cubic Yards Calculator for volume conversions, and the Cubic Feet Calculator for any volume — no signup required.
Related tools: Concrete Slab Calculator · Cubic Yards Calculator · Cubic Feet Calculator · Square Footage Calculator · Deck Calculator · Stair Calculator