Concrete Square Feet to Yards Calculator
Enter your slab area in square feet and thickness in inches to get cubic yards for ready-mix ordering. Includes short-load fee warnings, quarter-yard rounding, bag count alternatives, and a cost estimate at your local price per yard.
📐 Square Feet to Cubic Yards Converter
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Concrete Coverage Chart
How much concrete you need per square foot at different thicknesses — 4", 5", 6" and more.
View Chart →The Math Behind This Conversion
Depth Conversion
Your slab thickness in inches is divided by 12 to get decimal feet. A 4-inch slab becomes 0.333 feet. This step is required because area is measured in square feet but volume needs a feet-based depth.
Volume in Cubic Feet
Square footage is multiplied by the decimal depth. 400 sq ft × 0.333 ft = 133.2 cubic feet. This is the raw volume of concrete your project requires before any waste allowance.
Cubic Feet to Cubic Yards
Divide cubic feet by 27, since one cubic yard contains exactly 27 cubic feet (3 ft × 3 ft × 3 ft). 133.2 ÷ 27 = 4.93 cubic yards, per the standard formula used by ready-mix suppliers nationwide.
Waste and Rounding
A waste factor (5-15%) is applied, then the result is rounded up to the nearest quarter or half yard to match how suppliers sell concrete. This prevents ordering short on pour day.
Square Footage Coverage Lookup by Thickness
Find how many square feet one cubic yard covers at common slab thicknesses. Use this table to sanity-check your calculator result or estimate coverage without entering exact numbers.
| Thickness | Sq Ft per Cubic Yard | Cubic Yards per 100 Sq Ft | Common Use |
|---|---|---|---|
| 2 in | 162 ft² | 0.62 yd³ | Overlays, resurfacing |
| 3 in | 108 ft² | 0.93 yd³ | IRC minimum floor slab |
| 3.5 in | 92.5 ft² | 1.08 yd³ | IRC 2024 §R506.1 minimum |
| 4 in | 81 ft² | 1.23 yd³ | Patios, sidewalks |
| 5 in | 64.8 ft² | 1.54 yd³ | Light-duty driveways |
| 6 in | 54 ft² | 1.85 yd³ | Standard driveways, garages |
| 8 in | 40.5 ft² | 2.47 yd³ | Commercial, heavy vehicles |
Coverage figures calculated using Area × Depth ÷ 27. Source: Team Elmer's Concrete Materials Calculator methodology.
Why Square Feet Doesn't Equal Cubic Yards
Square feet measures a flat area. Cubic yards measures volume, which requires a third dimension: depth. A 400 sq ft patio and a 400 sq ft driveway need different amounts of concrete because one is 4 inches deep and the other might be 6 inches deep.
Ready-mix suppliers price and deliver concrete by the cubic yard, not by square footage. Skipping the depth conversion is the single most common reason DIYers order the wrong amount of concrete. One cubic yard always equals 27 cubic feet, regardless of the shape of your slab.
This calculator exists because most online converters only handle simple length-times-width-times-height math. Real slabs often start from a known area (from a site plan, a fence line, or a previous quote) rather than raw dimensions, which is why area-to-volume conversion deserves its own tool.
Sample Calculation Scenarios
🏠 Backyard Patio
Area: 320 sq ft
Thickness: 4 in (0.333 ft)
Waste factor: 10%
Raw volume: 320 × 0.333 = 106.6 ft³ = 3.95 yd³
With 10% waste: 4.34 yd³
Order size: 4.5 yd³ (rounded to nearest 1/4)
At under 6 yards, expect to ask about short-load fees when calling suppliers.
🚗 Two-Car Driveway
Area: 640 sq ft
Thickness: 6 in (0.5 ft)
Waste factor: 10%
Raw volume: 640 × 0.5 = 320 ft³ = 11.85 yd³
With 10% waste: 13.04 yd³
Order size: 13.25 yd³ (rounded to nearest 1/4)
This exceeds a single 10-yard truck. Confirm with your supplier whether a second truck or larger mixer is needed.
🧱 Small Shed Footing
Area: 64 sq ft
Thickness: 4 in (0.333 ft)
Waste factor: 5%
Raw volume: 64 × 0.333 = 21.3 ft³ = 0.79 yd³
With 5% waste: 0.83 yd³
Bag alternative: ~37 bags of 80 lb premix
Under 1 cubic yard is often cheaper and easier with bagged premix than ordering ready-mix delivery.
Mistakes That Lead to Ordering the Wrong Amount
Forgetting to convert inches to feet
Using "4" directly instead of "4/12 = 0.333" in the depth calculation inflates the result by 12 times. Always convert thickness to decimal feet before multiplying by area.
Confusing cubic feet with cubic yards
Suppliers quote and bill in cubic yards. Ordering "133 cubic feet" instead of "4.93 cubic yards" causes confusion and can lead to a wildly wrong truck order if misread as yards.
Skipping the waste factor entirely
Exact mathematical volume rarely survives real-world pours. Spillage, subgrade dips, and form flex typically consume 5 to 10% extra material. Ordering the bare minimum risks a mid-pour shortage.
Not rounding to supplier increments
Most ready-mix plants sell in quarter-yard increments, not exact decimals like 4.93. Round up before calling, or the supplier will round for you, sometimes to your disadvantage.
Ignoring short-load fees on small orders
Orders under roughly 6 cubic yards often trigger a flat short-load fee near $100 in 2026. This fee is easy to miss until the final invoice if it is not budgeted upfront.
Ordering Logistics and Code Context
Truck Capacity
Standard ready-mix trucks carry about 10 cubic yards. Orders approaching or exceeding this may require multiple trucks or a volumetric mixer, which prices per yard used rather than per truckload.
Minimum Slab Codes
IRC 2024 §R506.1 sets a 3.5-inch minimum for residential concrete floor slabs. Local jurisdictions may require more for driveways or garages. Verify with your local building department before pouring.
Unloading Time Windows
Most suppliers allow 45 minutes of free unloading time per truck. Waiting time beyond that can cost $3 to $5 per minute, so have your site, forms, and crew ready before the truck arrives.
Regional Price Differences
2026 ready-mix pricing runs roughly $115–$140/yd in the South, $120–$145/yd in the Midwest, $145–$175/yd on the West Coast, and $150–$185/yd in the Northeast, per industry pricing surveys.
Frequently Asked Questions
Multiply your square footage by the slab thickness in feet (inches divided by 12), then divide by 27. For example, 400 square feet at 4-inch thickness: 400 × (4/12) = 133.3 cubic feet, then 133.3 ÷ 27 = 4.94 cubic yards.
At a standard 4-inch thickness, one cubic yard covers about 81 square feet. At 6 inches, coverage drops to about 54 square feet. Coverage always shrinks as thickness increases, since 27 cubic feet spreads over less area.
Most ready-mix trucks carry roughly 10 cubic yards. Orders under 6 to 10 cubic yards typically trigger a short-load fee, often a flat $100 charge or about $40 per undelivered yard as of 2026. Coordinating with a nearby pour or using a volumetric mixer can help avoid this fee.
Yes. Suppliers sell in quarter-yard increments, and most contractors add 5 to 10 percent waste factor. If your raw math shows 4.94 yards, ordering 5.25 yards with waste included is standard practice.
An 80 lb premix bag yields about 0.60 cubic feet. Since one cubic yard equals 27 cubic feet, you need roughly 45 bags per cubic yard. For 60 lb bags (0.45 ft³ yield), that rises to about 60 bags per yard.
No. Once you know the area of any shape in square feet, the volume conversion uses the same formula: area × depth in feet ÷ 27. Only the area calculation differs by shape; the volume step stays identical.
Cubic feet is used for smaller material calculations like bag counts. Cubic yards is the unit ready-mix suppliers use for pricing and delivery. One cubic yard equals exactly 27 cubic feet. Confirm which unit your supplier quotes before ordering.
Sources and Methodology
- International Residential Code (IRC) 2024 §R506.1 — Minimum 3.5-inch residential concrete floor slab thickness.
- ACI 360R-10 — Guide to Design of Slabs-on-Ground, thickness recommendations for patios and driveways.
- Team Elmer's Concrete Materials Calculator methodology — Area × Depth ÷ 27 volume formula: teamelmers.com
- 2026 ready-mix concrete pricing data ($120–$185/yd national range, short-load fee estimates): Midwest Precast Contractor, March 2026
- Quikrete and Sakrete product specifications — 80 lb, 60 lb, and 40 lb bag cubic foot yields.
Last reviewed: July 2026. Reviewed by site author.
⚠️ Disclaimer
This calculator provides estimates for planning purposes. For permitted structural work, foundations, multi-story construction, retaining walls over 4 feet, and commercial projects, calculations must be verified by a licensed structural engineer per IBC 2024 §1604. ConcreteCalculate.com is not liable for structural decisions made from these estimates.
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