Garage Slab Calculator
Estimate concrete yards, bags, rebar, and cost for a garage slab
Length of the garage slab
Width of the garage slab
Slab thickness (4 in is standard)
80 lb Bags
—
bags
Rebar Mats
—
mats
Cubic Yards
—
cu yd
Estimated Cost
—
USD
Disclaimer: Results are estimates based on standard formulas. Not a substitute for professional advice from a licensed contractor, engineer, or architect. Verify all calculations before making purchasing or construction decisions.
How to Use This Calculator
Pouring a garage slab? Getting the concrete quantity right means you won't run short mid-pour or pay for overage you don't need.
- Enter the length and width of the garage slab
- Set the thickness (4 in for cars, 6 in for trucks)
- Review cubic yards, bag count, and rebar mats
- Compare ready-mix vs bagged concrete against the cost estimate
Expert Insights
Smart analysis for your Garage project
Bag vs Ready-Mix
Each 80 lb bag yields ~0.6 cu ft. A typical 2-car slab needs 300+ bags — ready-mix delivery from a truck is far cheaper for pours over 2 cubic yards.
Rebar Mat Spacing
We estimate one rebar mat per 64 sq ft (an 8x8 ft sheet). Mats sit on chairs at mid-depth so the steel engages when the concrete is loaded.
Thickness Selection
4 inches handles passenger cars. Step up to 5-6 inches for SUVs and trucks, and 6-8 inches for heavy equipment or RV parking.
Calculation Formula
Volume (cu ft) = Length x Width x (Thickness / 12)
Cubic yards = Volume / 27
80 lb bags = ceil(Volume / 0.6)
Rebar mats = ceil((Length x Width) / 64)
Estimated cost = ceil(Cubic yards x $6 per cu yd)
Garage Slab Thickness Comparison
| Slab Thickness | Typical Use | Rebar / Wire | Cost Impact |
|---|---|---|---|
| 4 inches | Standard garage, light vehicles | #3 rebar @ 24" or wire mesh | Baseline |
| 5 inches | Heavy vehicles, SUVs | #4 rebar @ 18" | +25% |
| 6 inches | Heavy trucks, RVs | #4 rebar @ 12" | +50% |
| 8 inches | Commercial / workshops | #5 rebar @ 12" | +100% |
Authority References
Our calculations are based on guidelines and standards from these authoritative sources:
- American Concrete Institute (ACI) — ACI 332 Residential & ACI 360R Guide to Slabs-on-Ground. Learn more
- International Residential Code (IRC) — R404 Foundation & R309 Garage Slab Requirements. Learn more
- Portland Cement Association (PCA) — Concrete Slab Construction Guides. Learn more
Frequently Asked Questions
How thick should a garage slab be?
A 4-inch slab is standard for passenger vehicles. Use 5-6 inches for SUVs and trucks, and 6-8 inches for heavy equipment, RVs, or commercial use.
How many bags of concrete do I need for a garage slab?
Each 80 lb bag yields about 0.6 cubic feet. A 24x24 ft, 4-inch slab needs roughly 320 bags. For slabs over 2 cubic yards, ready-mix delivery is far cheaper than bagged concrete.
Do I need rebar in a garage slab?
Yes. Rebar or wire mesh controls cracking from vehicle loads and freeze-thaw. A typical layout uses #3 or #4 rebar mats spaced 24 inches on center, sized in 8x8 ft sheets.