How many bags of concrete make a cubic yard?

Approximately 45 bags of 80-pound mix or 60 bags of 60-pound mix equal one cubic yard of concrete. An 80-pound bag yields about 0.60 cubic feet of mixed concrete. For small jobs, bagged mix is practical, but for pours over 2 cubic yards, ready-mix is more cost-effective and consistent.

What is a good waste factor for concrete?

Use 10% for standard slabs and footings on flat, prepared subgrade. Use 15% for complex shapes, piers on uneven ground, or any pour where the form dimensions may not be perfectly uniform. Never order the exact calculated volume with zero waste factor.

What concrete strength (PSI) should I specify?

3,000 PSI is standard for residential footings and slabs not exposed to freezing. 3,500 PSI for driveways and exterior flatwork. 4,000 PSI for structural elements and areas with freeze-thaw cycles. Specify air entrainment for exterior concrete in climates with freezing temperatures.

How long does ready-mix concrete stay workable?

Ready-mix has approximately 90 minutes of working time from when water contacts cement. At 3,000 PSI standard mix without retarders, plan your pour, finishing, and jointing to complete within 60 to 75 minutes on warm days. Hot weather significantly accelerates set time.

Construction & EngineeringPopular

Concrete Volume Calculator

Calculate how many cubic yards or cubic meters of concrete you need for slabs, footings, columns, walls, and other pours. Includes waste factor and cost estimation.

Dimensions

Length (ft)

Width (ft)

Depth (in)

Waste Factor (%)

Typically 5-10% for slabs, 10-15% for complex forms.

Concrete Needed

Enter dimensions and click Calculate

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Introduction

Concrete suppliers sell ready-mix by the cubic yard, but most contractors think in feet and inches during planning. That unit gap causes ordering errors that delay pours or leave excess material to dispose of. A standard residential slab at 4 inches deep covers 81 square feet per cubic yard, meaning a 400 sq ft garage floor requires exactly 4.94 cubic yards before waste. Most contractors round up to 5.5 to account for ground irregularities, formwork variance, and spillage. Getting that number wrong costs real money: a short pour on a 10-yard order can mean an emergency same-day call to the plant at $50 to $100 per yard above standard rates, per NRMCA ready-mix industry guidelines. This concrete volume calculator handles slabs, footings, columns, and walls with automatic waste factor recommendations.

What This Calculator Does

This calculator determines the volume of concrete needed for slabs, footings, columns, piers, and walls. Enter dimensions in feet and inches for the selected shape. The output includes volume in cubic yards (the standard ordering unit), cubic feet, and cubic meters. For smaller jobs, it estimates the number of 60-pound and 80-pound pre-mix bags required. A configurable waste factor handles the additional material needed beyond the theoretical volume.

The Formula

Slab: V = L x W x (D/12) | Column: V = pi x (Diameter/24)^2 x H | All results divided by 27 for cubic yards

For rectangular slabs and footings, multiply length by width (both in feet) by depth converted from inches to feet by dividing by 12. For cylindrical columns and piers, calculate the circular area using pi times the radius squared (radius in feet = diameter in inches divided by 24), then multiply by height in feet. All cubic foot results are divided by 27 to convert to cubic yards. Waste factor is applied as a multiplier: 1.10 for standard pours, 1.15 for complex formwork.

Step-by-Step Example

Select shape and enter dimensions

Choose slab/footing for rectangular pours or column/pier for cylindrical forms. Example: 20 ft long by 10 ft wide slab at 4 inches deep.

Calculate base volume

20 x 10 x (4/12) = 66.67 cubic feet. Divide by 27: 2.47 cubic yards. This is the theoretical volume without any waste.

Apply waste factor

Add 10% for standard slabs on prepared grade: 2.47 x 1.10 = 2.72 cubic yards. Use 15% for complex formwork, uneven ground, or irregular shapes.

Determine ordering quantity

Round up to the nearest quarter yard since most plants sell in 0.25 cubic yard increments. Order 2.75 cubic yards. For bag concrete comparison: 2.72 cu yd x 27 = 73.4 cu ft. At 0.45 cu ft per 60-lb bag, you would need 163 bags, confirming ready-mix is more cost-effective.

Real-World Use Cases

Garage Floor Slab Pour

A concrete contractor quoting a 24 ft by 24 ft garage slab at 4 inches deep calculates: 24 x 24 x (4/12) / 27 = 7.11 cubic yards. Adding 10% waste: 7.82 cu yd, ordered as 8.0 cu yd. At $165 per cubic yard, material cost is $1,320 before fiber, admixtures, and finishing labor.

Foundation Footing System

A builder calculating continuous footings for a 40 ft by 28 ft foundation perimeter (136 linear feet) at 8 inches wide by 16 inches deep: 136 x (8/12) x (16/12) / 27 = 4.45 cubic yards. With 10% waste: 4.90 cu yd, ordered as 5.0 cu yd.

Deck Post Footings

Six 12-inch diameter by 36-inch deep cylindrical piers: each pier = pi x (6/12)^2 x 3 = 2.36 cu ft. Six piers = 14.14 cu ft = 0.52 cubic yards. With 15% waste: 0.60 cubic yards. At 0.45 cu ft per 60-lb bag, approximately 38 bags covers all six footings.

Comparison

Depth	Slab Area per Cubic Yard	Ready-Mix Threshold	Best Option
3 inches	108 sq ft	Under 1 yd	Bagged concrete
4 inches	81 sq ft	1-2 yards	Bagged or ready-mix
4 inches	81 sq ft	Over 2 yards	Ready-mix delivery
6 inches	54 sq ft	Any quantity over 1 yd	Ready-mix delivery

Common Mistakes to Avoid

Forgetting to convert depth from inches to feet. Entering 4 for a 4-inch slab instead of 0.333 feet produces a volume 12 times too large. Always divide inches by 12 before multiplying.
Ordering the bare calculated volume without a waste factor. Ground irregularities, form sag, and spillage always require extra. A 10% waste factor on a 5-yard pour means having a half-yard safety buffer at no ordering risk.
Confusing cubic feet and cubic yards at the plant. Suppliers price and deliver in cubic yards. One cubic yard equals 27 cubic feet. A slip on units means ordering one-third of what you need.
Not verifying plant minimums. Most ready-mix plants have a 1 cubic yard minimum order. Below that threshold, bagged concrete is more practical and economical.

Frequently Asked Questions

Accuracy and Disclaimer

Concrete volume calculations are estimates based on nominal dimensions. Actual volume needed may vary due to ground conditions, subgrade irregularities, formwork accuracy, and mix consistency. Always include a waste factor in your order. Consult your ready-mix supplier for mix design specifications and delivery requirements.

Conclusion

For pours over 2 cubic yards, ready-mix delivery is more economical and produces a more consistent mix than bagged concrete. Once you have your cubic yard figure, add it to the Material Cost Estimator alongside your rebar, form lumber, and finishing supplies for a complete pour budget. If you are reinforcing the slab, run the Rebar Spacing Calculator to determine bar count and linear footage before placing your steel order.