Concrete Slab Calculator

A concrete slab calculator estimates concrete volume for slabs, pads, and footings based on entered length, width, and thickness.

Concrete Slab Calculator

Unit System

Length (feet)

Width (feet)

Depth (inches)

Waste Factor

Price per Cubic Yard ($)

This concrete slab calculator is one of several construction calculators available on this site. Enter your slab dimensions below to estimate cubic yards, bags, and cost.

How to Use This Calculator

Enter slab width and length
Enter slab thickness
Select a waste factor
Enter local price per cubic yard
Calculate Results

Tips for Accurate Measurements

Measure twice - Always double-check your dimensions before ordering
Account for slopes - If your area isn’t level, measure depth at multiple points. Use the fraction to decimal chart to convert tape measure readings to decimal inches for precise depth entries
Include forms - Your slab area should be measured inside the forms. Check the lumber dimensions chart for actual board widths when building forms from dimensional lumber
Round up - It’s better to have a little extra than run short mid-pour

Understanding the Results

Cubic Yards

Cubic yards are the standard unit used when ordering ready-mix concrete from suppliers.

80lb Bags

An 80-lb bag of concrete mix yields approximately 0.6 cubic feet of concrete.

Estimated Cost

Based on your entered price per cubic yard. Actual costs vary by location, time of year, and delivery distance. Call local suppliers for accurate quotes.

Common Concrete Slab Projects

Typical slab thickness varies by project type and load requirements.

Project Type	Typical Depth	Notes
Patio	4 inches	Add rebar for durability
Sidewalk	4 inches	Consider expansion joints
Driveway	5-6 inches	Use fiber reinforcement. Estimate sub-base material with the gravel calculator
Garage Floor	6 inches	May need thicker edges. Plan finish flooring with the flooring calculator
Shed Pad	4 inches	Level ground first

Gravel Calculator — Estimate cubic yards and tons of gravel needed for sub-base preparation under concrete slabs, driveways, and walkways.
Flooring Calculator — Calculate square footage, boxes, and cost for laminate, vinyl plank, hardwood, or tile installed over a finished slab.
Lumber Dimensions Chart — Look up actual board dimensions for form boards, stakes, and framing lumber used in slab prep and construction.
Fraction to Decimal Chart — Convert tape measure fractions to decimals for accurate depth and dimension entries in this calculator.

Frequently Asked Questions

The following questions address common concrete slab measurement and estimation topics.

How do I calculate concrete for a slab?

Concrete volume is calculated by multiplying slab length, width, and depth to determine cubic feet, then dividing by 27 to convert to cubic yards. Waste factors are commonly applied to account for variation in forms and placement.

How much does a cubic yard of concrete weigh?

A cubic yard of concrete weighs approximately 4,050 pounds (about 2 tons). Weight affects transportation, handling, and equipment requirements.

What thickness should a concrete slab be?

Typical concrete slab thickness varies by use. Patios and sidewalks are commonly 4 inches thick, driveways are often 5–6 inches, and garage floors or load-bearing areas are frequently 6 inches or thicker.

How many 80lb bags of concrete make a cubic yard?

One cubic yard of concrete requires approximately 45 bags of 80-lb concrete mix. Bag quantities vary depending on total volume and slab dimensions.

Should I add extra concrete for waste?

Concrete estimates often include an additional 5–15% to account for waste. Lower percentages are typical for simple rectangular slabs, while higher percentages are used for complex shapes or variable site conditions.

Reference Resources

Concrete Slab Calculation Reference (PDF)