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Concrete Calculator

Calculate concrete volume in cubic feet and cubic yards, and determine premix bag quantities for slabs, footings, and patios.

Concrete Slab & Volume Calculator

Calculate cubic yards of ready-mix concrete and bagged premix required for slabs, patios, and footings.

in

4 inches standard for walkways and patios; 5-6 inches for vehicle driveways.

%

Contractors recommend adding 10% to account for uneven grade, soil settlement, and form deflection.

cu ft / bag (typical for standard high-strength mix; adjust if your bag label states a different yield)

Yield Attribution: 80 lb (0.60 cu ft) and 60 lb (0.45 cu ft) yields are standard manufacturer specifications (e.g., QUIKRETE® #1101, Sakrete High-Strength TDS). The 50 lb yield (~0.375 cu ft) is an editable proportional planning estimate (based on ~133 lbs/cu ft aggregate density) because 50 lb bags are not listed on cited commercial premix datasheets. Check your physical bag label for exact yields.

Recommended Ready-Mix Concrete Order
2.72 Yards

Exact slab volume: 2.47 cu yd (66.7 cu ft) + 10% safety buffer (73.3 cu ft total)

80 lb Bag Estimate123 Bags0.600 cu ft yield/bag (Manufacturer TDS)
Total Bagged Weight9,840 lbsApprox. 4.92 US Tons
Exact Slab Volume2.47 cu yd66.7 cubic feet
Surface Area200 sq ft20 ft × 10 ft
Calculation Steps
  • 1.Convert depth from inches to feet: 4" ÷ 12 = 0.333 ft
  • 2.Calculate surface footprint: 20.0 ft × 10.0 ft = 200.00 sq ft
  • 3.Calculate exact volume in cubic feet: 200.00 sq ft × 0.333 ft = 66.67 cu ft
  • 4.Convert cubic feet to cubic yards: 66.67 cu ft ÷ 27 = 2.47 cu yd
  • 5.Recommended order with 10% safety buffer: 2.47 × 1.10 = 2.72 cu yd (73.33 cu ft)
  • 6.80 lb premix bags: ceil(73.33 ÷ 0.6 cu ft/bag) = 123 bags (9,840 lbs / 4.92 tons)
  • 7.60 lb premix bags: ceil(73.33 ÷ 0.45 cu ft/bag) = 163 bags (9,780 lbs / 4.89 tons)
  • 8.Planning Note: 80 lb and 60 lb yields are typical manufacturer TDS values (QUIKRETE® #1101, Sakrete). The 50 lb yield (~0.375 cu ft) is an editable proportional planning estimate. Always verify yield on your product bag label.
⚠️Practical Transport & Hauling Considerations

Weight Warning: 123 bags of 80 lb concrete weigh approximately 9,840 lbs (4.92 tons).

  • Verify Vehicle Payload: Consumer 1/2-ton pickup trucks commonly have payload limits between 1,500 and 2,000 lbs (including driver, fuel, passengers, and cargo). Hauling multiple tons requires multiple trips or a rated utility trailer. Check your vehicle door-jamb Tire and Loading Information placard.
  • Bagged vs. Ready-Mix Truck Delivery: For projects exceeding roughly 1 to 2 cubic yards (approx. 45+ bags of 80 lb concrete), ordering a ready-mix concrete delivery truck eliminates hours of manual batch mixing. However, ready-mix companies often charge "short-load fees" for small orders (e.g. under 3–5 cubic yards). We recommend requesting local delivered quotes to compare total costs against bagged premix.

Mathematical Formula & Calculation Method

Volume (cu yd) = [Length (ft) × Width (ft) × Depth (in) / 12] / 27

Formula Components:

  • Depth in Feet = Depth in Inches ÷ 12
  • Volume (Cubic Feet) = Length (ft) × Width (ft) × Depth (ft)
  • Volume (Cubic Yards) = Volume (cu ft) ÷ 27
  • Recommended Order = Volume (cu yd) × (1 + Waste % / 100)
  • 80 lb Bags Needed = ceil(Recommended Volume (cu ft) ÷ Bag Yield) [Commercial Premix TDS: ~0.60 cu ft/bag]
  • Total Premix Weight (lbs) = Bags × Bag Weight

How It Works

1

Enter slab length and width in feet (or meters).

2

Enter slab thickness (depth) in inches (4" typical for walkways/patios, 5-6" for driveways).

3

Set waste margin (contractors recommend 10% for grade unevenness and form deflection).

4

Select preferred premix bag size (80 lb, 60 lb, or 50 lb).

5

View total cubic yards, bag count, total bagged weight in pounds/tons, and delivery logistics advice.

Practical Calculation Examples

10×20 ft Patio Slab at 4 Inches Deep (10% waste)

Pouring a backyard concrete patio with 10% extra for grade variations.

Step 1:Convert depth to feet: 4 in ÷ 12 = 0.333 ft.
Step 2:Slab volume: 10 × 20 × 0.333 = 66.67 cubic feet (2.47 cu yd).
Step 3:Add 10% safety buffer: 2.47 × 1.10 = 2.72 cubic yards (73.33 cu ft).
Step 4:Premix bags: ceil(73.33 ÷ 0.60 cu ft/bag) = 123 bags (80 lb).
Step 5:Weight check: 123 bags × 80 lbs = 9,840 lbs (4.92 US tons).
Outcome: Order 2.75 cubic yards of ready-mix truck delivery (4.92 tons exceeds pickup payload limits).

Important Assumptions & Estimator Guidance

  • 1 cubic yard of concrete equals 27 cubic feet.
  • Bag yields: 80 lb (~0.60 cu ft) and 60 lb (~0.45 cu ft) reflect commercial manufacturer technical data (QUIKRETE® #1101, Sakrete), while 50 lb (~0.375 cu ft) is an editable proportional planning estimate. Always check your product bag label.
  • Uneven subgrade excavation, soil compaction, and form deflection require a 10% buffer.
  • Consumer 1/2-ton pickup trucks generally carry 1,500 to 2,000 lbs maximum payload (including passengers and cargo); hauling tons of concrete requires multiple trips or truck delivery.
  • For projects exceeding roughly 1 to 2 cubic yards (~45+ bags), compare local ready-mix delivery quotes against bagged concrete, noting that batch plants often apply short-load fees for smaller truck deliveries.

Common Pitfalls & Mistakes to Avoid

Ordering the exact calculated yardage without buffer

Excavated soil is never perfectly flat, and forms deflect under wet concrete pressure, risking an expensive short pour.

Correction: Always add 10% extra ready-mix concrete to prevent cold joints.

Frequently Asked Questions

If your project requires more than 1 cubic yard (about 45 bags of 80 lb concrete), ordering a ready-mix truck is significantly faster, structurally more consistent, and easier on your back.

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