Concrete Yardage Calculator
This concrete yardage calculator estimates the total volume you need in cubic yards, cubic feet, and bagged mixes. Whether you are figuring out how much concrete do I need for a slab, setting posts, or planning a driveway, accurate calculations prevent cold joints and wasted truck fees.
How Do You Calculate Yards of Concrete?
A cubic yard is a standard unit of volume equaling 27 cubic feet. To find concrete yardage, multiply surface area by thickness in feet and divide by 27. One cubic yard weighs approximately 4,050 lbs based on typical concrete density (150 lbs per cubic foot).
• 1 Cubic Yard ($yd^3$) = 27 Cubic Feet ($ft^3$)
• 1 Cubic Yard = 46,656 Cubic Inches ($in^3$)
• 1 Cubic Yard = 0.764555 Cubic Meters ($m^3$)
• Concrete density = ~4,050 lbs per cubic yard (wet ready-mix concrete)
Concrete Volume Formulas & Examples
Use these standard formulas based on your project shape. For reliable pours, apply the square footage x depth formula and include a 10% waste factor / overage percentage for uneven subgrades.
1. Slabs, Patios, Sidewalks & Driveways
Volume (cu yds) = [Length (ft) × Width (ft) × (Slab Depth (in) / 12)] / 27Example: How many yards of concrete for a 10x10 slab at 4 inches thick?
1. Convert depth to feet: 4 in ÷ 12 = 0.333 ft.
2. Calculate cubic feet: 10 ft × 10 ft × 0.333 ft = 33.33 cu ft.
3. Convert cubic feet to cubic yards: 33.33 ÷ 27 = 1.23 cubic yards (or 1.35 cu yds with 10% waste).
2. Concrete Needed for Fence Posts Calculator & Sonotubes
Volume (cu yds) = [π × (Hole Diameter (in) / 24)² × Depth (ft)] / 27Example: 12-inch diameter hole, 3 feet deep:
Radius = 0.5 ft. Volume = 3.14159 × (0.5)² × 3 = 2.356 cu ft. Divided by 27 = 0.087 cu yds per hole (~4 bags of 80 lb mix).
3. Solid Concrete Steps
Volume (cu yds) = [Width (ft) × (Tread (in) / 12) × (Riser (in) / 12) × (Steps × (Steps + 1) / 2)] / 27Accounts for the stacked volume of every step without duplicate form calculations.
Pre-Mixed Bag Breakdown & Yield Chart
When mixing on-site using bagged products like Quikrete or Sakrete, check this reference chart to see how many bags make up 1 cubic yard (27 cubic feet):
| Bag Weight | Yield (Cu Ft) | Bags per Cubic Yard | Typical Project Use |
|---|---|---|---|
| 80 lb Bag | 0.60 cu ft | 45 Bags | Footings, pads, structural slabs |
| 60 lb Bag | 0.45 cu ft | 60 Bags | Walkways, small patios, curbs |
| 50 lb Bag | 0.375 cu ft | 72 Bags | Fast-setting post concrete |
| 40 lb Bag | 0.30 cu ft | 90 Bags | Crack repairs, fence post collars |
Pour Planning & Quality Essentials
1. Slab Depth / Thickness (Inches): A standard pour of how much concrete for a sidewalk 4 inches thick covers 81 sq ft per yard. Residential driveways require 5 to 6 inches of thickness to support vehicle weight without surface failure.
2. Sub-Base Compaction: Pour over a minimum of 4 inches of crushed, compacted gravel rather than native soil. This reduces settling and gives the slab a firm, level foundation.
3. PSI / Concrete Mix Ratio: Use a minimum 3,000 to 3,500 PSI mix for patios and walkways. Step up to a 4,000 PSI mix with rebar or wire mesh for driveways and cold-climate freeze-thaw protection.
4. Ordering Buffer: Always order an extra 10% to account for form board flex, uneven ground excavations, and slight spillage during discharge.
Frequently Asked Questions
How do you calculate yards of concrete?
Multiply length by width in feet to get the area, multiply by thickness in feet (inches divided by 12) for total cubic feet, and divide by 27. Add a 10% buffer to cover ground variations and spillage.
How much does a yard of concrete cover?
One cubic yard covers 81 square feet at 4 inches thick. At 6 inches thick, it covers 54 square feet, and at 3 inches thick, it covers 108 square feet.
How many bags of concrete equal a yard?
It takes 45 bags of 80 lb mix, 60 bags of 60 lb mix, or 90 bags of 40 lb mix to equal one full cubic yard (27 cubic feet).
How thick should a concrete slab be for a driveway?
A driveway should be poured at least 4 to 5 inches thick for typical cars and SUVs, and 6 inches thick with rebar grid reinforcement if parking heavy work trucks or campers.
Is it cheaper to buy concrete by the yard or by the bag?
Bagged concrete is cheaper for small tasks requiring under 1 cubic yard. For larger jobs requiring over 1.5 to 2 cubic yards, ordering a ready-mix concrete delivery truck is faster, produces a stronger mix, and eliminates hours of hand-mixing labor.
Concrete Yardage Calculator
Total Concrete Required (With 10% Waste)
Pre-Mixed Bag Count Options
* Estimated yardage and bag counts include the selected waste factor and are rounded up to whole units. Verify subgrade grade level and form rigidity before ordering batch delivery.
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