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Concrete Calculator

Calculate concrete volume in cubic yards for slabs, footings, columns, and walls from dimensions.

Concrete Slab Volume & Cost Estimator

Ordering exactly the mathematical volume of concrete is a rookie mistake. Subgrades are never level, forms bow under pour pressure, and spills happen. A 10% waste factor is the professional standard for residential slabs. Running short mid-pour means a cold joint — a structural weakness that can cause cracking along the seam.

Thickness Presets

5–10% standard

Material only

Thickness = 4" / 12 = 0.3333 ft
Volume = 20 × 20 × 0.3333 = 133.33 ft³
Cubic yards = 133.33 / 27 = 4.94 yd³
With waste = 4.94 × (1 + 10%) = 5.43 yd³
Cost = 5.43 × $150/yd³ = $815
Pure Volume
4.94
yd³ (no waste)
Order This Much (+10%)
5.43
yd³ with waste factor
≈ 1 truck load (8 yd³/truck)
Estimated Material Cost
$815
Concrete only (ex. labor, forms, finish)
Volume & Cost by Thickness (20 × 20 ft, 10% waste factor)
3.5" Sidewalk
4.75 yd³ / $713
4" Slab/Patio
5.43 yd³ / $815
5" Driveway
6.79 yd³ / $1,019
6" Light Truck
8.15 yd³ / $1,222

Practical Example

A 20 × 20 ft driveway at 4" thick:

Pure volume = 20 × 20 × (4/12) / 27 = 400 × 0.333 / 27 = 4.94 cubic yards
With 10% waste = 4.94 × 1.10 = 5.43 cubic yards to order
At $150/yd³ = $814 in concrete material costs

Standard concrete trucks deliver 8–10 yards. You'd order 1 partial truck. Anything under ~5 yards usually incurs a short-load fee of $50–$150. Factor this into your budget for small pours.

💡 Field Notes

  • Why waste factor matters: Subgrades are never perfectly flat — even a surveyed grade has low spots. Forms bow outward under the weight of wet concrete. Running short mid-pour forces a "cold joint" where fresh concrete is poured on partially-set concrete, creating a visible line and structural weakness. Always order more than the math says.
  • Thickness is cubed in importance: Doubling thickness from 4" to 8" doubles the concrete volume (and cost), but more than doubles load capacity. A 6" slab carries heavy equipment (forklifts, RVs); a 4" slab is for foot traffic and passenger vehicles only. Using the wrong thickness is a structural failure waiting to happen.
  • Mix design and PSI: Standard residential slabs use 3,000–4,000 PSI mix. Driveways should be 4,000 PSI minimum. Industrial floors require 4,500–5,000 PSI with fiber reinforcement. This calculator estimates volume only — always confirm mix design with your ready-mix supplier based on the load application.
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What is Concrete Volume Estimation for Slabs, Footings, and Walls?

Concrete is ordered by the cubic yard (27 cubic feet per yard). Accurate volume estimation is critical — under-ordering stops the pour mid-job leaving cold joints, while over-ordering wastes hundreds of dollars. The calculation converts your measured dimensions into cubic yards with an appropriate overage factor.

Mathematical Foundation

Volume to Cubic Yards
Vyd3=L×W×T27V_{yd^3} = \frac{L \times W \times T}{27}
LL= Length of the pour area (feet).
WW= Width of the pour area (feet).
TT= Thickness of the pour (feet — convert inches by dividing by 12).
2727= Cubic feet per cubic yard — the standard unit sold by ready-mix plants.

Laws & Principles

  • Always Order 10% Extra: Ready-mix plants cannot perfectly fill every void and form. Substrate irregularities, form deflection, and spillage consume material. The industry standard is to order a minimum of 5–10% above your calculated volume. Running short during a monolithic pour creates a cold joint — a structural weakness that can fail under load.
  • Minimum Slab Thickness by Code: Residential driveways require a minimum 4-inch slab. Structural slabs supporting vehicle loads require 6 inches. Footings must extend below the frost line and meet local code minimums.
  • Mix Strength Selection: Residential flatwork typically uses 3,500–4,000 PSI mix. Structural footings and columns require 4,000 PSI minimum. High-traffic commercial slabs often specify 5,000 PSI.

Step-by-Step Example Walkthrough

" A homeowner needs to pour a concrete driveway that is 20 feet wide, 40 feet long, and 4 inches thick. "

  1. 1. Convert thickness to feet: 4 inches ÷ 12 = 0.333 feet.
  2. 2. Calculate cubic feet: 20 × 40 × 0.333 = 266.7 cubic feet.
  3. 3. Convert to cubic yards: 266.7 ÷ 27 = 9.88 cubic yards.
  4. 4. Add 10% waste: 9.88 × 1.10 = 10.87 cubic yards.
  5. 5. Round up to nearest half-yard: Order 11 cubic yards.
Final Result: Order 11 cubic yards of concrete for the 20×40 ft driveway at 4-inch thickness with a standard 10% overage factor.

Quick Answer: How to Calculate Concrete Volume

Multiply your slab's Length × Width × Depth (all in feet) to get cubic feet, then divide by 27 to convert to cubic yards — the unit ready-mix plants use for ordering. Always add 10% for waste.

Fast example: A 10 ft × 10 ft slab at 4 inches thick = 10 × 10 × 0.333 = 33.3 cubic feet ÷ 27 = 1.23 cubic yards. Order 1.5 yards (with waste).

The Concrete Volume Formula

Cubic Yards = (L × W × D) ÷ 27

  • L= Length of the pour area in feet
  • W= Width of the pour area in feet
  • D= Depth / Thickness in feet — convert inches by dividing by 12 (e.g., 4 in = 0.333 ft)
  • 27= Cubic feet per cubic yard (1 yd³ = 3 ft × 3 ft × 3 ft)

💡 Unit tip: Always work in feet. Convert inches to feet before multiplying — it's the single most common mistake that leads to under-ordering.

Real-World Concrete Calculation Examples

Example 1: 10×10 ft Patio (4″ thick)

  1. Step 1: Convert depth → 4 ÷ 12 = 0.333 ft
  2. Step 2: Cubic feet → 10 × 10 × 0.333 = 33.3 ft³
  3. Step 3: Cubic yards → 33.3 ÷ 27 = 1.23 yd³
  4. Step 4: Add 10% waste → 1.23 × 1.10 = 1.35 yd³

→ Order 1.5 cubic yards

Example 2: 24×24 ft Garage Slab (6″ thick)

  1. Step 1: Convert depth → 6 ÷ 12 = 0.5 ft
  2. Step 2: Cubic feet → 24 × 24 × 0.5 = 288 ft³
  3. Step 3: Cubic yards → 288 ÷ 27 = 10.67 yd³
  4. Step 4: Add 10% waste → 10.67 × 1.10 = 11.74 yd³

→ Order 12 cubic yards

Concrete Cost Estimation Guide

Ready-mix concrete typically costs $125 – $150 per cubic yard for standard residential mixes (3,500–4,000 PSI). High-strength commercial mixes (5,000+ PSI) run $150 – $200+ per yard.

Cost Item Typical Range
Ready-mix concrete (per yd³)$125 – $150
Short-load fee (< 5 yd³)$50 – $200
Saturday / overtime delivery$75 – $150 surcharge
Pump truck (if needed)$500 – $1,200
Fiber / rebar reinforcement$25 – $75 / yd³

💡 Always get quotes from 2–3 local plants. Prices vary significantly by region and aggregate type. Ask if the quote includes a minimum load fee.

Pro Tips & Common Mistakes to Avoid

  • ✓ Always order 10% extra. Substrate irregularities, form deflection, spillage, and slight miscalculations consume material. Running short mid-pour creates a cold joint — a structural weakness that can crack under load.
  • ✓ Never pour on frozen ground. Concrete poured on frozen subgrade will heave and crack as the ground thaws. Ground temp should be above 40°F and rising for at least 3 days after the pour.
  • ✓ Compact your sub-base. A minimum 4-inch compacted gravel base is standard for residential slabs. Poorly compacted subgrade is the #1 cause of long-term cracking and settling.
  • ✗ Don't add extra water on-site. Adding water to the mix after delivery increases workability but destroys strength. Every gallon of extra water added per yard can reduce strength by 200 PSI.
  • ✗ Don't skip expansion joints. Control joints should be cut at 8–12 ft intervals for slabs. Without them, cracks form randomly — typically in the worst possible locations.

Frequently Asked Questions

How many 80 lb bags of concrete are in a cubic yard?

One cubic yard requires approximately 45 bags of 80 lb concrete (e.g., Quikrete or Sakrete). Each 80 lb bag yields roughly 0.60 cubic feet, and there are 27 cubic feet in a yard: 27 ÷ 0.60 = 45 bags. For small pours under 1 yard, bagged concrete is cost-effective. For anything larger, ready-mix is faster and often cheaper.

How thick should a concrete driveway be?

Standard residential driveways are poured at 4 inches thick. For driveways that will support heavy vehicles — RVs, delivery trucks, heavy pickup trucks — increase to 6 inches and use 4,000 PSI mix with rebar or wire mesh reinforcement. Some municipalities require a minimum 5 inches for permitted driveways.

What is a cubic yard of concrete in terms I can picture?

One cubic yard is a cube that is 3 feet × 3 feet × 3 feet — roughly the size of a large household appliance. At an average weight of 4,050 lbs per yard, a single cubic yard of concrete weighs about 2 tons. A standard transit-mix truck holds 8–10 cubic yards (16–20 tons).

How long does concrete take to cure?

Concrete reaches 70% of its design strength in 7 days and full cure (28-day strength) after about a month. You can typically walk on it after 24–48 hours and drive on it after 7 days in warm weather. Cold weather significantly slows curing — keep it above 50°F and protected from freezing for at least 3 days.

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