How much concrete do I need for a 10x10 slab?
At 4 inches thick, a 10 × 10 ft slab needs 33.3 cubic feet, or about 1.23 cubic yards. With 10% waste, order about 1.4 cubic yards or roughly 62 of the 80 lb bags.
Slab volume and bags
Concrete Slab Calculator
100% Free — No Sign Up Required
Enter slab length, width, and depth to calculate concrete in cubic yards, bags, or cubic meters — instantly and for free.
Cubic yards
1.63
Cubic feet
44.00
Cubic meters
1.25
Estimated bags
74
Includes a 10% waste factor. This estimate is for planning only; forms, subgrade and delivery conditions can change the final order.
Quick Cost Estimate
Estimated total cost
$252.59
Quick Cost Estimate multiplies estimated cubic yards by your unit price. It excludes labor, delivery, pumping, reinforcement, base prep and tax.
How to Use the Concrete Slab Calculator
Using this concrete slab calculator takes three measurements. First, measure the length and width of the slab forms in feet — measure the forms themselves, not the drawing, because as-built dimensions often differ from the plan. Second, enter the slab thickness in inches; the calculator converts it automatically. Third, set a waste factor, typically 5–10%, to cover uneven subgrade, spillage, and finishing losses. The slab concrete calculator instantly returns the volume in cubic yards, cubic feet, and cubic meters, plus the number of 40 lb, 60 lb, or 80 lb bags. You can switch any dimension between feet, inches, yards, and meters using the unit toggle next to each input, so metric projects work just as well as imperial ones.
Concrete Slab Formula Explained
To calculate concrete slab volume by hand, use the formula: length × width × (depth ÷ 12) = cubic feet, then divide by 27 to get cubic yards. Depth is divided by 12 because it is usually measured in inches while the other dimensions are in feet, and the division by 27 converts cubic feet to cubic yards — there are 3 × 3 × 3 = 27 cubic feet in one cubic yard. Take a 20 ft × 15 ft garage slab poured at 5 inches: 20 × 15 × (5 ÷ 12) = 125 cubic feet, and 125 ÷ 27 = 4.63 cubic yards. With a 10% waste factor the order becomes about 5.1 cubic yards. If you would rather see the answer purely in yards, our concrete yard calculator runs the same math and supports a second area. For bag-based projects, the concrete bag calculator divides the volume by the yield of each bag size.
Common Slab Thicknesses
Slab thickness drives both the concrete slab calculation and the durability of the finished pour. Walkways and patios that only carry foot traffic are commonly poured at 4 inches. Garage floors and residential driveways that carry cars are typically 4 to 6 inches, with 6 inches preferred where pickups or trailers park. Slabs for workshops, RV pads, or light equipment often run 6 inches or more, sometimes with thickened edges. Shed bases are usually 4 inches. These are planning conventions, not engineering advice: soil conditions, climate, reinforcement, and local building codes can all change the required thickness, so confirm structural slabs with a professional before you pour.
Tips for Ordering Concrete
Once the concrete slab estimator gives you a volume, round up rather than down — running short mid-pour creates a cold joint that permanently weakens the slab. Ready mix suppliers usually sell in quarter-yard increments with a minimum load, and short-load fees can make very small deliveries expensive; below roughly one cubic yard, bagged concrete is often cheaper and simpler. Tell the dispatcher the slab thickness and finish you plan, confirm the truck can reach the forms, and have help on site, because a yard of concrete weighs about two tons and sets on its own schedule. The Quick Cost Estimate below the calculator multiplies your yardage by a price per cubic yard for a fast material-only budget check.
Concrete Calculators by Project Type
Concrete Slab Calculator
Use length, width and thickness for floors, patios and rectangular slabs.
Concrete Pad CalculatorEstimate square, rectangular or circular pads with a quick cost field.
Concrete Yard CalculatorConvert dimensions into cubic yards, cubic feet and cubic meters.
Concrete Bag CalculatorEstimate 40 lb, 60 lb and 80 lb bags after waste is added.
Frequently Asked Questions
What thickness should I enter for a slab?
Enter the planned finished thickness in inches. Patios and walkways are commonly 4 inches; driveways and garage floors are often 4 to 6 inches.
Does the slab calculator include waste?
Yes. The waste factor you set is applied before cubic yards and bag counts are calculated, and bag counts round up to whole bags.
Can I calculate a concrete slab in metric units?
Yes. Switch the unit toggle on any input to meters or centimeters and read the result in cubic meters.