How Much Concrete Do I Need Per Square Foot?
A precise unit-rate reference guide displaying exact cubic feet, cubic yards, and bag quantities required per square foot across all standard flatwork thicknesses.
At 4" thickness: 0.333 cu. ft. (0.01235 cu. yds) per square foot.
For every 100 square feet of a standard 4-inch residential patio, you need 1.23 cubic yards (33.33 cu. ft.) of concrete—or 62 bags (80 lb) with a 10% safety buffer.
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Concrete Unit Rate Table: Material Needed for 1 Square Foot
This reference chart displays exact volumetric units and dry bag fractions required to pour 1 single square foot at various slab depths:
| Slab Thickness | Cubic Feet / sq ft | Cubic Yards / sq ft | 80 lb Bags / sq ft | 60 lb Bags / sq ft | Area per 1 Yard³ |
|---|---|---|---|---|---|
| 2 inches (50 mm) | 0.1667 cu. ft. | 0.00617 yd³ | 0.278 bags | 0.370 bags | 162.0 sq. ft. |
| 3 inches (75 mm) | 0.2500 cu. ft. | 0.00926 yd³ | 0.417 bags | 0.556 bags | 108.0 sq. ft. |
| 3.5 inches (90 mm • 2×4) | 0.2917 cu. ft. | 0.01080 yd³ | 0.486 bags | 0.648 bags | 92.6 sq. ft. |
| 4 inches (100 mm • std) | 0.3333 cu. ft. | 0.01235 yd³ | 0.556 bags | 0.741 bags | 81.0 sq. ft. |
| 5 inches (125 mm) | 0.4167 cu. ft. | 0.01543 yd³ | 0.694 bags | 0.926 bags | 64.8 sq. ft. |
| 6 inches (150 mm) | 0.5000 cu. ft. | 0.01852 yd³ | 0.833 bags | 1.111 bags | 54.0 sq. ft. |
| 8 inches (200 mm) | 0.6667 cu. ft. | 0.02469 yd³ | 1.111 bags | 1.481 bags | 40.5 sq. ft. |
Concrete Quantities for Benchmark Project Square Footages (at 4" Depth)
To quickly estimate typical job footprints, use this breakdown for common square footage milestones at a standard 4-inch slab thickness (including a 10% safety buffer):
| Surface Area | Nominal Volume | +10% Order Volume | 80 lb Bags (+10%) | 60 lb Bags (+10%) | Recommended Batch Order |
|---|---|---|---|---|---|
| 10 sq. ft. (e.g. small AC pad) | 0.12 yd³ (3.33 ft³) | 0.14 yd³ (3.67 ft³) | 7 bags | 9 bags | Bagged Mix |
| 50 sq. ft. (e.g. small walkway) | 0.62 yd³ (16.67 ft³) | 0.68 yd³ (18.33 ft³) | 31 bags | 41 bags | Bagged Mix |
| 100 sq. ft. (e.g. 10×10 patio) | 1.23 yd³ (33.33 ft³) | 1.36 yd³ (36.67 ft³) | 62 bags | 82 bags | 1.5 yd³ Ready-Mix |
| 200 sq. ft. (e.g. 10×20 patio) | 2.47 yd³ (66.67 ft³) | 2.72 yd³ (73.33 ft³) | 123 bags | 163 bags | 3.0 yd³ Ready-Mix |
| 400 sq. ft. (e.g. 20×20 garage) | 4.94 yd³ (133.33 ft³) | 5.43 yd³ (146.67 ft³) | 245 bags | 326 bags | 5.5 yd³ Ready-Mix |
| 500 sq. ft. (e.g. wide driveway) | 6.17 yd³ (166.67 ft³) | 6.79 yd³ (183.33 ft³) | 306 bags | 408 bags | 7.0 yd³ Ready-Mix |
| 1,000 sq. ft. (large flatwork) | 12.35 yd³ (333.33 ft³) | 13.58 yd³ (366.67 ft³) | 612 bags | 815 bags | 14.0 yd³ (2 Truckloads) |
* For full multi-size slab comparisons, see our guide on concrete needed for a 10×10 slab and common slab sizes.
How Per-Square-Foot Volume Relates to Finished Project Costs
Knowing the concrete volume per square foot allows you to estimate raw material costs versus turn-key contractor installation pricing:
- Raw Ready-Mix Material Cost: At $150 per cubic yard delivered, concrete material alone costs approximately $1.85 per square foot for a 4-inch slab (0.01235 yd³ × $150 = $1.85) or $2.78 per square foot for a 6-inch slab.
- Turn-Key Installed Project Cost: Full contractor flatwork (including excavation, compacted crushed stone subbase, formwork lumber, #4 steel rebar reinforcement, pouring, screeding, and broom/trowel finishing) typically ranges from $6.00 to $12.00 per square foot for standard residential flatwork.
For a full breakdown of site prep, labor, and finishing fees, see our comprehensive guide on how much does concrete cost per square foot in 2026.
Frequently Asked Questions About Concrete Per Square Foot
How much concrete do I need per square foot for a 4-inch slab?
For a 4-inch thick slab, each 1 square foot requires 0.3333 cubic feet (1/3 cu. ft.) or approximately 0.01235 cubic yards of concrete. In terms of bagged mix, you need 0.556 of an 80-lb bag per square foot (meaning 1 eighty-pound bag covers 1.80 square feet).
How much concrete is needed per square foot for a 6-inch slab?
For a 6-inch thick slab, each 1 square foot requires exactly 0.5000 cubic feet (1/2 cu. ft.) or 0.01852 cubic yards. In bagged mix, this equals 0.833 of an 80-lb bag per square foot (1 eighty-pound bag covers 1.20 square feet).
How much concrete do I need for 100 square feet?
At a standard 4-inch thickness, 100 square feet requires 33.33 cubic feet (1.23 cubic yards) of concrete nominal volume. With a 10% safety buffer, plan for 36.67 cubic feet (1.36 cubic yards), which equals 62 eighty-pound bags (or 82 sixty-pound bags).
What is the formula for cubic yards per square foot?
The formula is: Cubic Yards per Square Foot = Thickness in Inches ÷ 324. For a 4-inch slab: 4 ÷ 324 = 0.012346 yd³/sq ft.
How many bags of concrete do I need per square foot?
Divide the cubic feet required per square foot by your bag yield: For 80 lb bags (0.60 cu ft yield) at 4" thickness: (4 ÷ 12) ÷ 0.60 = 0.556 bags per sq ft. For 60 lb bags (0.45 cu ft yield) at 4" thickness: (4 ÷ 12) ÷ 0.45 = 0.741 bags per sq ft.