How many 80 lb concrete bags make a cubic yard?

One 80 lb bag of pre-mixed concrete yields approximately 0.60 cubic feet. Since one cubic yard contains 27 cubic feet: 27 ÷ 0.60 = 45 eighty-pound bags. With a 10% waste margin, order 50 bags.

How many 60 lb bags of concrete make a cubic yard?

One 60 lb bag yields approximately 0.45 cubic feet of mixed concrete. Therefore, it takes exactly 60 bags of 60 lb concrete (or 66 bags with 10% contingency) to make one cubic yard.

How does the concrete calculator for footings calculate cylindrical volume?

For round post holes and cylindrical footings: Volume = π × Radius² × Depth. Divide by 27 to convert cubic feet to cubic yards. For example, a 12-inch diameter (6-inch radius = 0.5 ft) footing that is 4 ft deep requires 3.1416 × 0.25 × 4 = 3.14 cu ft (approx. 5.2 bags of 80 lb concrete).

Why should I always add a 10% waste contingency?

Ground subbases are rarely perfectly level, wooden form boards bow outward slightly under the hydrostatic weight of wet cement, and minor spillage occurs during mixing and pouring. A 10% margin ensures you never run short mid-pour.

When should I order a concrete truck instead of mixing bags?

If your project requires more than 1 cubic yard (45 eighty-pound bags, or 3,600 lbs of concrete), ordering a ready-mix concrete delivery truck saves hours of intense physical labor and ensures consistent strength.

Concrete Calculator – Slabs, Footings & Cubic Yards

How to Estimate Concrete Slabs, Footings & Bags

1

Select Structure Type (Slab or Round Footing)

Choose Rectangular Slab for patios, driveways, and floors, or Round Column / Footing for deck post holes.

2

Enter Length, Width & Thickness

Input dimensions in feet and inches (e.g., 10 ft length, 12 ft width, 4 in depth).

3

Include Waste Allowance & Get Bag Count

Add a recommended 10% waste buffer to view exact cubic yards for ready-mix delivery or exact bags of 60 lb and 80 lb dry premix.

Masonry & DIY Construction Features

Slab & Footing Modes

Calculate rectangular slabs, pads, sidewalks, as well as cylindrical round post footings.

Cubic Yards & Meters

Direct conversion into cubic yards for ready-mix trucks and cubic meters for international building standards.

Online Concrete Calculator: Slabs, Footings, Cubic Yards & Bags

Concrete is the single most consumed manufactured material on Earth—second only to water as civilization's most utilized resource. From residential patios, garage floors, sidewalks, and driveway slabs to structural post footings, fence piers, and foundation retaining walls, concrete provides the solid foundation of human infrastructure.

However, pouring concrete is an irreversible, time-sensitive operation. Because wet concrete undergoes irreversible exothermic chemical hydration—typically beginning to set within 90 minutes of mixing—estimation errors carry severe consequences. Under-ordering causes disastrous structural "cold joints," while over-ordering results in wasted materials and transit return penalties.

MiniToolBar's free concrete calculator delivers an accurate civil estimation workstation. Functioning as a concrete slab calculator, concrete floor calculator, concrete volume calculator, and concrete yard calculator, our tool allows you to determine how much concrete do I need calculator answers in concrete calculator cubic yards and cubic feet, alongside exact bag counts with our concrete bags calculator and 80 lb concrete bags calculator.

How Much Concrete Do I Need Calculator: The Cubic Yard Formula

To use our concrete calculator for slab length width and depth, apply the core volumetric engineering formula:

Convert all dimensions to feet: Length (ft) × Width (ft) × Depth (ft). Because slab thickness is given in inches, divide depth by 12:
Cubic Feet = Length (ft) × Width (ft) × (Thickness (inches) / 12)
Convert to Cubic Yards: Since one cubic yard contains 27 cubic feet (3 ft × 3 ft × 3 ft):
Cubic Yards = Cubic Feet / 27 = (Length × Width × Thickness (in)) / 324
Add 10% Waste Margin: Excavations are rarely perfectly level, and forms flex slightly under the hydrostatic weight of wet cement:
Ordered Volume = Calculated Cubic Yards × 1.10

Worked Slab Example: A 10 ft by 20 ft patio slab at 4 inches thick:

(10 × 20 × 4) / 324 = 800 / 324 ≈ 2.47 Cubic Yards (+10% buffer = 2.72 Yards)

Slab Thickness to Cubic Yards and Bag Count Estimation Matrix

The table below shows total concrete requirements across various square footages and standard slab depths (including a recommended 10% contingency buffer):

Slab Area (Sq Ft)	4" Slab (Yards / 80-lb Bags)	5" Slab (Yards / 80-lb Bags)	6" Heavy Slab (Yards / 80-lb Bags)	Recommended Pour Method
50 sq ft (5' × 10')	0.68 yd³ (34 bags)	0.85 yd³ (43 bags)	1.02 yd³ (51 bags)	Pre-mixed bags / Wheelbarrow mix
100 sq ft (10' × 10')	1.36 yd³ (68 bags)	1.70 yd³ (85 bags)	2.04 yd³ (102 bags)	Towable mixer or Short-load truck
200 sq ft (10' × 20')	2.72 yd³ (136 bags)	3.40 yd³ (170 bags)	4.07 yd³ (204 bags)	Ready-Mix Concrete Delivery Truck
500 sq ft (20' × 25')	6.79 yd³ (340 bags)	8.49 yd³ (425 bags)	10.19 yd³ (510 bags)	Full Ready-Mix Truck Delivery
1,000 sq ft (25' × 40')	13.58 yd³ (679 bags)	16.98 yd³ (849 bags)	20.37 yd³ (1,019 bags)	Multi-Truck Commercial Pour

Concrete Calculator for Footings & Round Post Columns

For cylindrical deck posts, fence foundations, and round Sonotubes, use our concrete calculator for footings based on cylindrical stereometry:

Cylindrical Volume = π × Radius² × Depth = 3.14159 × (Diameter (in) / 24)² × Depth (ft)

Worked Footing Example: Pouring four 12-inch diameter post footings (radius = 0.5 ft) extending 4 feet deep:

Single Hole = 3.1416 × (0.5)² × 4 = 3.1416 cu ft ÷ 27 = 0.116 cu yds (Approx. 5.2 bags of 80-lb concrete)

For all 4 footings: 4 × 5.2 = 21 bags of 80-lb pre-mix concrete (or 23 bags with a 10% safety margin).

Pre-Mixed Concrete Bags: 40-lb, 60-lb, and 80-lb Yield Matrix

When shopping at home improvement stores, commercial pre-mixed dry concrete comes in standard bag weights. The table below details yields and requirements per cubic yard:

Bag Size	Yield (Cubic Feet)	Bags per 1 Cubic Yard (Exact)	Bags with 10% Waste Buffer	Primary Application
40 lb Bag	0.30 cu ft	90 Bags	99 Bags	Small DIY repairs, post anchors, light stepping stones
50 lb Fast-Setting	0.375 cu ft	72 Bags	80 Bags	Quick-set fence post installations with no mixing required
60 lb Bag	0.45 cu ft	60 Bags	66 Bags	Sidewalks, air conditioner pads, mailbox footings
80 lb Bag (Industry Standard)	0.60 cu ft	45 Bags	50 Bags	Patio slabs, structural footings, steps, garage pads

Concrete Compressive Strength Classes & Structural PSI Ratings

Depending on structural load requirements, concrete mixes are rated by their 28-day compressive strength in Pounds per Square Inch (PSI):

Strength Rating	Minimum 28-Day PSI	Standard Construction Applications
Residential Footings	2,500 PSI	Non-structural walkway slabs, fence post collars, garden curbing.
Standard Slabs & Patios	3,000 PSI	Standard patio slabs, residential sidewalks, basement floors.
Driveways & Vehicle Pads	4,000 PSI	Automotive driveways, heavy equipment storage pads, freeze-thaw climate paving.
Commercial & Industrial	5,000+ PSI	Commercial warehouses, bridge abutments, industrial floor slabs.

Explore Related Construction & Quantitative Calculators on MiniToolBar

Need to compute material contingency percentages or plan project timelines? Explore our other tools:

Calculate material waste contingency percentages and mix ratios with our Percentage Calculator.
Schedule construction phases and calculate concrete 28-day full cure dates with our Date Calculator.
Log contractor crew shifts and track labor hours on job sites with our Hours Calculator.

Frequently Asked Questions

Find clear answers to common questions about our tools, formulas, and privacy.

For a rectangular slab: Volume (Cubic Feet) = Length (ft) × Width (ft) × Depth (ft). Convert to cubic yards by dividing by 27: Cubic Yards = (Length × Width × Depth) / 27. For a 10 ft × 12 ft slab at 4 inches (0.333 ft) thick: 10 × 12 × 0.333 = 40 cu ft ÷ 27 = 1.48 cubic yards.