CUBIC YARDS & PRE-MIX BAG TAKEOFF
Concrete Slab & Bag Calculator
Calculate cubic yards and exact number of 80lb and 60lb pre-mix bags needed for slabs, patios, footings, and sidewalks with sub-base gravel and rebar reinforcing.
Slab Dimensions & Thickness
144 sq ft+10%
Order Ready-Mix Concrete Truck Delivery (1.96 Cu Yds)
Mixing 89 bags by hand will take over 8 hours of intensive labor. A ready-mix truck costs approximately $140–$180/yd and pours the entire slab in under 30 minutes.
2D CONCRETE SLAB CROSS-SECTION & SUB-BASE1.96 Cu Yards | 89 Bags (80-lb)
Footprint: 12′ × 12′ (144 sq ft) 4,000 PSI Mix Recommended
Total Volume Required
1.96 Yds³
89 Bags (80-lb)
Or 118 Bags (60-lb)
| Material Spec | Quantity | Est. Cost |
|---|---|---|
| 80-lb High-Strength Concrete | 89 bags | $556.25 |
| Compacted Gravel Bed (4") | 2.5 tons | $104.53 |
| Welded Wire Reinforcing (5×10') | 4 sheets | $66.00 |
How the Math Works: Concrete Slab & Bag Formulas
Verified construction takeoff formulas & live variable substitution (IRC / IBC Code Baseline)
1Slab Surface Footprint= 144 sq ft
Standard FormulaArea = Length (L) × Width (W)
Live Values Substituted12 ft × 12 ft
Total surface area to be formed with 2x lumber.
2Concrete Volume in Cubic Yards (with Waste)= 1.96 Cubic Yards
Standard FormulaCubic_Yards = [(L × W × (Thickness ÷ 12)) ÷ 27] × (1 + Waste ÷ 100)
Live Values Substituted[(12 × 12 × (4 ÷ 12)) ÷ 27] × 1.10
1 cubic yard = 27 cubic feet. Adds buffer for uneven excavation subgrade.
3Number of 80-lb Concrete Bags= 89 Bags (80-lb)
Standard FormulaBags_80lb = ⌈Total_Cubic_Feet ÷ 0.60 cu ft/bag⌉
Live Values Substituted⌈48.0 cu ft × 1.10 ÷ 0.60⌉
Standard commercial 80lb Sakrete / Quikrete bag yields 0.60 cubic feet mixed.
Jobsite Engineering Notes & Constants
- One cubic yard equals 27 cubic feet. A standard 80-lb bag yields 0.60 cubic feet of mixed concrete, requiring 45 bags per cubic yard.
- 4,000 PSI air-entrained mix is recommended for exterior slabs exposed to freeze-thaw cycles.
Frequently Asked Questions: Concrete Bag Calculator
Verified trade answers for construction estimation, building codes, and waste allowances
There are 45 bags of 80-lb concrete in one cubic yard (27 cubic feet). One 80-lb bag yields approximately 0.60 cubic feet of mixed concrete. For 60-lb bags, you need 60 bags per cubic yard (each yields 0.45 cu ft).
Length (ft) × Width (ft) × (Thickness (inches) / 12) ÷ 27. For example, a 10 ft × 10 ft patio at 4 inches thick: 10 × 10 × (4 / 12) = 33.33 cubic feet ÷ 27 = 1.23 cubic yards. Adding a standard 10% buffer gives 1.35 cubic yards (61 bags of 80-lb concrete).