CONCRETE
CALCULATOR
Calculate exact concrete volumes in cubic yards, cubic feet & cubic meters. Get bag counts and cost estimates for slabs, footings, columns & stairs.
— Bag Count Estimator (with waste)
CONCRETE VOLUME
FORMULAS
All formulas below produce cubic feet. Divide by 27 to convert to cubic yards. Multiply by 0.0283168 to convert to cubic meters.
Slab / Footing
Length (ft) × Width (ft) × Depth (in) ÷ 12 = ft³. Divide by 27 for yd³.
Wall / Column
Length (ft) × Width (in ÷ 12) × Height (ft) = ft³.
Circular Column
Pi × radius² (ft) × height (ft) = ft³. Convert diameter to feet before calculating.
Stairs
Each step adds volume. Step n volume = n × rise × run × width (converted to ft³).
RECOMMENDED
SLAB THICKNESS
| Application | Min. Thickness | Typical Thickness | Notes |
|---|---|---|---|
| Sidewalk / Walkway | 3 in | 4 in | Pedestrian traffic only |
| Patio / Pool Deck | 4 in | 4–5 in | Add rebar for large areas |
| Residential Driveway | 4 in | 5–6 in | Use 3000 psi or higher |
| Garage Floor | 4 in | 5–6 in | Control joints every 10 ft |
| Commercial Driveway | 6 in | 6–8 in | Heavy vehicle traffic |
| Foundation Slab | 4 in | 6–8 in | Per local building code |
| Retaining Wall | 8 in | 10–12 in | Depends on wall height |
CONCRETE BAG
COVERAGE CHART
| Bag Size | Yield (ft³) | Yield (yd³) | Coverage at 4 in |
|---|---|---|---|
| 40 lb bag | 0.30 ft³ | 0.011 yd³ | ~0.9 sq ft |
| 50 lb bag | 0.375 ft³ | 0.014 yd³ | ~1.1 sq ft |
| 60 lb bag | 0.45 ft³ | 0.017 yd³ | ~1.35 sq ft |
| 80 lb bag | 0.60 ft³ | 0.022 yd³ | ~1.8 sq ft |
| 90 lb bag | 0.67 ft³ | 0.025 yd³ | ~2.0 sq ft |
FREQUENTLY ASKED
QUESTIONS
A 10×10 foot slab at 4 inches thick requires approximately 1.23 cubic yards of concrete (about 33 cubic feet). At 6 inches thick, you would need roughly 1.85 cubic yards. Always add at least 10% extra for waste. That means ordering about 1.35 yd³ for a standard 4-inch slab. Use the calculator above for exact figures.
Divide cubic feet by 27 to get cubic yards. There are 27 cubic feet in one cubic yard (3 ft × 3 ft × 3 ft = 27 ft³). For example, 50 cubic feet ÷ 27 = 1.85 cubic yards. Ready-mix concrete is sold by the cubic yard, so this conversion is essential when ordering.
For a 10×10 ft slab at 4 inches thick (with 10% waste), you need approximately 61 bags of 80 lb concrete. Each 80 lb bag yields 0.60 cubic feet, and the slab needs about 33.3 ft³ plus 10% waste = 36.6 ft³ total. Divide by 0.60 = 61 bags. For large slabs like this, ready-mix delivery is usually more cost-effective.
For most residential projects, 3000 PSI (20 MPa) concrete is sufficient for driveways, patios, and floors. Use 3500–4000 PSI for heavy-duty driveways or slabs exposed to freeze-thaw cycles. Footings and foundations typically call for 2500–3000 PSI. Check local building codes for specific requirements in your area.
As a general rule, use bagged concrete for projects under 1 cubic yard (27 cubic feet). For anything larger, ready-mix concrete delivered by truck is more economical and provides more consistent mixing. Most ready-mix suppliers have a minimum order of 1 cubic yard. Factor in minimum delivery charges when comparing costs.
A standard concrete mix ratio is 1:2:3 — one part cement, two parts sand, and three parts aggregate (gravel) by volume, plus water. The water-cement ratio typically ranges from 0.45 to 0.60. Lower water ratios produce stronger concrete. Pre-mixed bags are pre-proportioned so you only add water according to the bag instructions.
TIPS FOR A SUCCESSFUL
CONCRETE POUR
Getting your concrete calculation right is just the start. Here are the most important factors for a durable, long-lasting pour.
Always Add Waste
Order 10–15% more than your calculated volume. Uneven sub-base, form overruns, and spillage are unavoidable. Running short mid-pour causes cold joints and structural weakness.
Sub-Base Preparation
Compact the sub-base thoroughly. Use 4–6 inches of compacted gravel for slabs. A stable, level sub-base prevents cracking and settling over time.
Control Joints
Place control joints every 8–12 feet in slabs to control cracking. Joints should be ¼ the depth of the slab. This directs cracking to the joints rather than random locations.
Curing is Critical
Keep concrete moist for at least 7 days after pouring. Use curing compound, plastic sheeting, or wet burlap. Concrete reaches full strength at 28 days — avoid heavy loads until then.