20 × 20 slab concrete table
| Thickness | Cubic yards | 60 lb bags | 80 lb bags | Estimated material cost |
|---|---|---|---|---|
| 4 in | 4.94 | 297 | 223 | $1,559–$1,450 bagged / $815 ready-mix |
| 5 in | 6.17 | 371 | 278 | $1,948–$1,807 bagged / $1,019 ready-mix |
| 6 in | 7.41 | 445 | 334 | $2,336–$2,171 bagged / $1,222 ready-mix |
What this slab size is commonly used for
This footprint is commonly considered for a single-car garage, large patio, or workshop. Before ordering, confirm the finished dimensions after forms are installed. A base that is not level can change the amount needed, and thickened edges or footings are separate from the flat slab calculation. If the project includes a curb, steps, thickened perimeter, or isolated pads, calculate those volumes separately and add them to the order.
When to use ready-mix
Bagged concrete can be practical for small pours, repairs, and locations where a truck cannot reach. As the number of bags rises, mixing, moving, and placing the material becomes a major part of the job. Ready-mix is usually worth comparing for a slab this size when the pour must stay continuous, the site has delivery access, or the finish window is short. Ask the supplier about minimum loads, delivery fees, slump, and the strength specification required for your use.
How much waste should I add?
Ten percent is a reasonable planning allowance for many straightforward forms. Increase it when the excavation is irregular, the subbase is uneven, or access makes a second delivery difficult. The live calculator above recalculates the bag and yard estimate when you change thickness or waste.
Frequently asked questions
Does this include rebar or mesh?
No. Reinforcement, base gravel, vapor barrier, forms, delivery, labor, and finishing supplies are separate from the concrete volume.
Should I order exactly the calculated amount?
Use the table as an estimate, then confirm the final quantity with your supplier using the actual product yield and your site measurements.