Concrete Garage Floor Calculator
A standard 24×24 ft 2-car garage slab at 6 inches thick takes 10.67 cubic yards of concrete — about one full ready-mix truck. Enter your garage dimensions and thickness below for volume, bag-equivalent count, and reinforcement guidance.
Pro Tips
- →Garage floors should be 6 inches thick for vehicle weight
- →Include rebar reinforcement in a grid pattern
- →Slope floor slightly toward door for drainage (1-2%)
- →Add a vapor barrier under the slab
- →Consider a higher PSI mix (4,000-5,000) for durability
Includes 10% waste factor
That's typically a professional pour. See costs ↓
4 short emails from Dave: what a fair quote should land at for your slab, the scope changes that swing it ±$500, and whether DIY is actually cheaper at your volume. Reply anytime — he'll review your real quote.
Cost Estimate
Estimated material costs for your project
Recommendation: Ready-Mix Concrete
For projects over 1 cubic yard, ready-mix is typically more economical and easier to work with.
528 bags × 80lb
11.73 cubic yards + delivery
576 sq ft × $3.00–$8.00/sq ft
Prices vary by location and time. Contact local suppliers for accurate quotes.
For general step-by-step instructions, read our complete Garage Floor Thickness and When To Use Rebar.
What This Calculator Covers
Volume estimates for residential garage slabs from single-car to oversized 3-car layouts, at the 4-, 5-, and 6-inch thicknesses you'll actually pour. A 24×24 ft 2-car slab at 6 inches takes 10.67 cubic yards — one full ready-mix truck. For installed cost rather than just material volume, run the same dimensions through the garage floor cost calculator.
The practical decision on thickness comes down to what the floor will hold: pure parking and storage works fine at 4 inches; lifts, jack stands, and shop equipment need 6.
Garage Slab Volume by Size
| Garage Type | Footprint | Square Feet | Volume (cu yd, 6 in) | Truck Loads |
|---|---|---|---|---|
| 1-car (compact) | 12 × 20 ft | 240 | 4.4 | 0.5 (short load) |
| 1-car (standard) | 14 × 22 ft | 308 | 5.7 | 0.6 (short load) |
| 2-car (standard) | 20 × 20 ft | 400 | 7.4 | 0.75 |
| 2-car (oversized) | 24 × 24 ft | 576 | 10.7 | 1 full truck |
| 3-car | 30 × 24 ft | 720 | 13.3 | 1.5 |
| 3-car (deep) | 36 × 24 ft | 864 | 16.0 | 1.5–2 |
Add 10% for waste and order to the next quarter-yard. Below about 3 cubic yards, ready-mix companies typically charge a $75–150 short-load fee.
Why 6 Inches and 4,000 PSI
A car parked on a garage slab puts roughly 750–1,000 lbs through each tire contact patch (about 6 sq in) — meaning point loads in the 125–165 PSI range. That's well within a 4-inch slab's capacity for static parking. The reasons to go thicker:
- Jack stands and floor jacks — concentrated loads of 1,500–4,000 lbs through pads as small as 4 sq in (250–1,000 PSI point loads). 6 inches keeps these from punching through.
- Shop equipment — lifts, presses, and welders concentrate weight on small footprints; manufacturers typically spec 6-inch minimum.
- Freeze-thaw cycling — in cold climates, the extra mass and 4,000 PSI mix resist scaling from de-icer drip-off.
4,000 PSI also gets you better workability for the broom finish that doubles as slip resistance when wet.
Rebar, Mesh, and Vapor Barrier
- Reinforcement — #4 (1/2-inch) rebar in a 24-inch grid at mid-slab depth is the residential standard. The cheaper alternative is 6×6 W1.4/W1.4 welded wire mesh — adequate for cars but not preferred under a lift.
- Vapor barrier — 10-mil polyethylene over the gravel base, lapped 12 inches and taped at seams. Essential under heated garages and any garage in a humid climate.
- Gravel base — 4 inches of compacted 3/4-inch crushed stone over native subgrade. Compact in 2-inch lifts.
- Control joints — saw-cut at 10–12 ft spacing within 24 hours of finishing, depth of one-quarter slab thickness (1.5 in for a 6-inch slab). For a 24×24 garage, two cuts dividing the slab into quarters is typical.
Slope and Drainage
Slope the entire slab 1–2% toward the garage door for water drainage. For a 24-foot-deep garage, that's roughly 3–6 inches of fall from the back wall to the door threshold — enough to move water out without making the floor feel tilted.
In snow-belt climates, this slope handles slush and snowmelt off vehicles in winter. Skip the slope and any standing water under a parked car becomes a freeze-spall problem within a few seasons.
For pricing the full installation including subgrade prep, rebar, vapor barrier, and finishing, see the companion garage floor cost calculator.